Telah hadir buku / Tutorial yang anda tunggu-tunggu.

“ Exploring of Injection Moulding Machine “

Buku ini saya susun berdasarkan pengalaman sebagai teknisi mesin Injeksi selama 16 tahun. Kurun waktu tersebut bukanlah waktu yang singkat untuk dapat memahami dan menelanjangi teknologi mesin Injection. Dalam perjalanan tersebut saya sudah banyak disiksa dan kenyang makan asam garam mesin plastik dimana karir saya sebagai teknisi dimulai dengan menangani jenis mesin control relay mekanik sampai control microcomputer.
Tujuan mempublikasikan tutorial ini untuk membantu bagi anda yang baru terjun didunia cetak mencetak produk plastik dengan media mesin Injection disamping sebagai operator, setter atau teknisi lapangan yang baru terjun lantas bingung mencari informasi mesin tersebut.
Sebenarnya banyak informasi yang dapat anda peroleh via Internet namun terpotong-potong dan kurang terdefinisi bila dibandingkan dengan mesin yang anda hadapi. Tak heran karena seperti dunia elektronik, mesin Injection mengalami perkembangan pesat setiap tahunnya. Untuk itulah buku/tutorial ini saya susun secara terstruktur sehingga anda dapat menguasai teknologi mesin Injection secara cepat dan tepat.
Bagaimanakah cara anda mendapatkan buku ini ?. gampang berikut informasinya :

Judul buku : Exploring of Injection Moulding Machine.
Pengarang : Yonni Muhazir.
Bahasa pengantar : Bahasa Indonesia.
Tebal buku : 110 Halaman, Hard Cover.
Statistik buku :21.601 words, Arrial Narrow 12 Point, 1 space.
Kertas : A4, Sidu 70 grams, Cannon printing iP 1980.
Harga : Rp 200.000,-
Dalam kota bebas ongkos kirim.
Dalam propinsi Jatim dikenakan bea kirim Rp 15.000,-
Luar propinsi Jatim dikenakan bea kirim Rp 30.000,-

Cara pemesanan :
Via wessel pos alamatkan ke : Jalan Laksda Adi Sucipto gang 8 no 7 Malang 65125. Buku akan dikirim via paket pos 3 hari setelah uang dicairkan. Kenapa pakai cara tradisional ?. Cara lama lebih disukai karena relatif aman daripada open via transfer bank yang banyak resiko. Bila anda harus melakukan transfer, dapat via BCA yang terlebih dahulu telepon saya kemudian ikuti wizardnya.
Bila ada masalah dalam pengiriman atau lain hal, dapat kontak melalui HP XL 081 803 842 554 a/n : Yonni Muhazir. Atau email ke Yonni_1967@yahoo.co.id .

Mahal amat harga bukunya ?……itu mungkin komentar dalam hati anda………., ..…Sekedar informasi, berikut kalkulasinya :

Beaya cetak 110 halaman x 1000 = Rp 110.000,-
Beaya Hard cover = Rp 30.000,-
Lain lain Rp 15.000,- (beaya transportasi mondar-mandir)

Jadi saya hanya untung tak lebih dari Rp 60.000,- perbukunya dan itu sebagai kompensasi saya sebagai upah lembur mengetik dan lembur ngeprint dan yang terutama harga Informasi yang berharga demi untuk anda. Harga buku sebanding dengan kerja keras saya melekan tiap malam ngetik dan peluh keringat saya mengumpulkan informasi. Anda tidak akan kecewa deh, dari pada anda banyak menghabiskan uang di Internet surfing kesana-kemari. Untuk bahan pertimbangan ( seperti membeli kucing dalam sarung eh..karung dan membuat anda kecewa nanti ), sebelum memesan buku silakan mengintip isinya disini :

Harga dapat berubah-ubah sesuai harga kertas, harga tinta, dan perubahan lain hal. Jadi buruan pesan sekarang juga. Tunggu penerbitan jilid kedua dan ketiga yang tentunya lebih seru dan hot. Dijamin.

Jilid 2 ( Coming soon ) : Hidraulica of Injection Moulding Machine.
Jilid 3 ( Coming soon ) : Getting Start with Injection Moulding Machine.

Maaf tidak melayani pengiriman dalam bentuk soft copy. Semoga bermanfaat bagi semua. Amin……….

Berikut listingnya :

‘———Program aplikasi sekuensi injection moulding machine——’
‘Dibuat oleh : Yonni Muhazir
‘Nim : 0510450391/E
‘Fakultas teknik / elektronika
‘Uwiga Malang, January 2009
‘———————————————————————’

$regfile = “m8535.dat”
$crystal = 4000000
$baud = 9600

Dim Automatis As Bit , Y1 As Bit , Ls_close As Bit ‘Y1 adalah coil mold closing– output portb.0/ y1 ‘
Config Porta = Input
Set Porta.0
Port A.0 Alias Automatis
Port A.1 Alias Ls_close ‘automatis tombol start automatis–input porta.0′
Config Portb = Output
Set Portb.0
Portb.0 Alias Y1

Do

If Automatis = 1 Then
Y1 = 1
Else
If Ls_close = 1 Then ‘ls_close adalah stop closing–input port : input porta.1′
Y1 = 0
End If
End If

Dim Ls_clamping As Bit , Y2 As Bit ‘y2 adalah yoke clamping–portb.1′
Set Porta.2
Porta.2 Alias Ls_clamping ‘ls_clamping ;input porta.2
Set Portb.1 Alias Y2
Port A.2 Alias Ls_clamping
If Ls_clamping = 1 Then
Y2 = 1
Else
Waitms 100
Print “timer clamping” ‘timer generation clamping
End If

Dim , Y3 As Bit , Ls_iu_stop As Bit ‘y3=yoke IU maju–output portb.2′,
Set Porta.3
Porta.3 Alias Ls_iu_stop ‘Ls IU maju stop– input porta.3
Set Portb.2
Portb.2 Alias Y3
If Y2 = 0 Then
Y3 = 1
Else
If Ls_iu_stop = 1 Then
Y3 = 0
End If
End If

Dim Y4 As Bit , Ls_inj_end As Bit
Set Porta.4 ‘ls_inj_end = input porta.4,
Porta.4 Alias Ls_inj_end ‘y4=yoke injection-output portb.4′
Set Portb.4
Portb.4 Alias Injection Yoke
If Y3 = 0 Then
Y4 = 1
Else
Waitms 200 ‘timer injection berjalan 500ms’
Print “timer injection on”
If Ls_inj_end = 1 Then
Y4 = 0
End If
End If

Dim Plasticizing As Bit , Ls_plast As Bit , Decomp As Bit , Ls_decomp As Bit , Cooling As Bit
Set Portb.5
Portb.5 Alias Plasticizing ‘y5 =plasticizing – output portb.5′
Set Porta.5
Porta.5 Alias Ls_plast ‘ ls_stop plasticizing – input porta.5′
Set Portb.6
Portb.6 Alias Decomp ‘ y6-decompression : output portb.6
Set Porta.6
Porta.6 Alias Ls_decomp ‘ ls decompression stop ; input port a.6

If Y4 = 0 Then
Plasticizing = 1 ‘ saat plasticizing,
Else
If Ls_plast = 1 Then ‘ plasticizing berhenti
Plasticizing = 0
Else
If Ls_plast = 1 Then

Else
If Plasticizing = 0 Then
Decomp = 1

Else
If Ls_plast = 1 Then ‘mundurkan decompresi’
Decomp = 0

End
End If
End If
End If
End If
End If

Waitms 300 ‘ cooling time berjalan’
Print ” cooling time runing”

Dim Iu_ret As Bit , Ls_iu_ret_stop As Bit , Mold_opn As Bit , Ls_opn_stp As Bit

Set Portb.7
Portb.7 Alias Iu_ret ‘yoke injection unit mundur output portb.7′
Set Porta.7
Porta.7 Alias Ls_iu_ret_stop ‘ls IU stop mundur input porta.7′

Config Portc = Output ‘konfigurasi pin port c sebagai output’
Config Portd = Input ‘konfigurasi portd sebagai input’

Set Portc.0
Portc.0 Alias Mold_opn ‘yoke mold open–output portc.0′
Set Portd.0
Portd.0 Alias Ls_opn_stop ‘ls_open stop mold–input portd.0

If Decomp = 0 Then
Iu_ret = 1 ‘injection unit mundur
Else
If Ls_iu_ret_stop = 1 Then
Mold_opn = 1 ‘mould membuka penuh sampai ls stop tertekan’
Else
If Ls_opn_stp = 1 Then
Mold_opn = 0
End If
End If
End If

Dim Eject_maju As Bit , Eject_mundur As Bit , Ls_eject_maju As Bit , Ls_eject_mundur As Bit
Dim Multi_eject As Integer
Set Portc.1
Portc.1 Alias Eject_maju ‘portc.1 = eject maju – output portc.1′
Set Portd.1
Portd.1 Alias Ls_eject_maju ‘ls_eject maju = input portd.1
Set Portc.2
Portc.2 Alias Eject_mundur ‘ yoke eject_mundur = output_eject_mundur = output portd.2
Set Portd.2
Portd.2 Alias Ls_eject_mundur ‘ ls_stop_eject_mundur = input portd.2

For Multi_eject = 147 To 157 Step 3 ‘perintah multi eject/maju-mundur 3 step’

If Ls_opn_stp = 1 Then
Eject_maju = 1 ‘ejector maju sampai ls stop,
Else
If Ls_eject_maju = 1 Then
Eject_maju = 0
Else
If Ls_eject_maju = 1 Then
Eject_mundur = 1 ‘ejector mundur’
Else
If Ls_eject_mundur = 1 Then
Eject_mundur = 0
End If
End If
End If
End If
Next
‘
Print “Pause_time”
Waitms 340

Loop ‘perintah kembali ke program awal—begitu seterusnya’

End ‘end program’———Program aplikasi sekuensi injection moulding machine——’
‘Dibuat oleh : Yonni Muhazir
‘Nim : 0510450391/E
‘Fakultas teknik / elektronika
‘Uwiga January Malang 2009
‘———————————————————————’

$regfile = “m8535.dat”
$crystal = 4000000
$baud = 9600

Dim Automatis As Bit , Y1 As Bit , Ls_close As Bit ‘Y1 adalah coil mold closing– output portb.0/ y1 ‘
Config Porta = Input
Set Porta.0
Port A.0 Alias Automatis
Port A.1 Alias Ls_close ‘automatis tombol start automatis–input porta.0′
Config Portb = Output
Set Portb.0
Portb.0 Alias Y1
If Automatis = 1 Then
Y1 = 1
Else
If Ls_close = 1 Then ‘ls_close adalah stop closing–input port : input porta.1′
Y1 = 0
End If
End If

Dim Ls_clamping As Bit , Y2 As Bit ‘y2 adalah yoke clamping–portb.1′
Set Porta.2
Porta.2 Alias Ls_clamping ‘ls_clamping ;input porta.2
Set Portb.1 Alias Y2
Port A.2 Alias Ls_clamping
If Ls_clamping = 1 Then
Y2 = 1
Else
Waitms 100
Print “timer clamping” ‘timer generation clamping
End If

Dim , Y3 As Bit , Ls_iu_stop As Bit ‘y3=yoke IU maju–output portb.2′,
Set Porta.3
Porta.3 Alias Ls_iu_stop ‘Ls IU maju stop– input porta.3
Set Portb.2
Portb.2 Alias Y3
If Y2 = 0 Then
Y3 = 1
Else
If Ls_iu_stop = 1 Then
Y3 = 0
End If
End If

Dim Y4 As Bit , Ls_inj_end As Bit
Set Porta.4 ‘ls_inj_end = input porta.4,
Porta.4 Alias Ls_inj_end ‘y4=yoke injection-output portb.4′
Set Portb.4
Portb.4 Alias Injection Yoke
If Y3 = 0 Then
Y4 = 1
Else
Waitms 200 ‘timer injection berjalan 500ms’
Print “timer injection on”
If Ls_inj_end = 1 Then
Y4 = 0
End If
End If

Dim Plasticizing As Bit , Ls_plast As Bit , Decomp As Bit , Ls_decomp As Bit , Cooling As Bit
Set Portb.5
Portb.5 Alias Plasticizing ‘y5 =plasticizing – output portb.5′
Set Porta.5
Porta.5 Alias Ls_plast ‘ ls_stop plasticizing – input porta.5′
Set Portb.6
Portb.6 Alias Decomp ‘ y6-decompression : output portb.6
Set Porta.6
Porta.6 Alias Ls_decomp ‘ ls decompression stop ; input port a.6

If Y4 = 0 Then
Plasticizing = 1 ‘ saat plasticizing,
Else
If Ls_plast = 1 Then ‘ plasticizing berhenti
Plasticizing = 0
Else
If Ls_plast = 1 Then

Else
If Plasticizing = 0 Then
Decomp = 1

Else
If Ls_plast = 1 Then ‘mundurkan decompresi’
Decomp = 0

End
End If
End If
End If
End If
End If

Waitms 300 ‘ cooling time berjalan’
Print ” cooling time runing”

Dim Iu_ret As Bit , Ls_iu_ret_stop As Bit , Mold_opn As Bit , Ls_opn_stp As Bit

Set Portb.7
Portb.7 Alias Iu_ret ‘yoke injection unit mundur output portb.7′
Set Porta.7
Porta.7 Alias Ls_iu_ret_stop ‘ls IU stop mundur input porta.7′

Config Portc = Output ‘konfigurasi pin port c sebagai output’
Config Portd = Input ‘konfigurasi portd sebagai input’

Set Portc.0
Portc.0 Alias Mold_opn ‘yoke mold open–output portc.0′
Set Portd.0
Portd.0 Alias Ls_opn_stop ‘ls_open stop mold–input portd.0

If Decomp = 0 Then
Iu_ret = 1 ‘injection unit mundur
Else
If Ls_iu_ret_stop = 1 Then
Mold_opn = 1 ‘mould membuka penuh sampai ls stop tertekan’
Else
If Ls_opn_stp = 1 Then
Mold_opn = 0
End If
End If
End If

Dim Eject_maju As Bit , Eject_mundur As Bit , Ls_eject_maju As Bit , Ls_eject_mundur As Bit

Set Portc.1
Portc.1 Alias Eject_maju ‘portc.1 = eject maju – output portc.1′
Set Portd.1
Portd.1 Alias Ls_eject_maju ‘ls_eject maju = input portd.1
Set Portc.2
Portc.2 Alias Eject_mundur ‘ yoke eject_mundur = output_eject_mundur = output portd.2
Set Portd.2
Portd.2 Alias Ls_eject_mundur ‘ ls_stop_eject_mundur = input portd.2

If Ls_opn_stp = 1 Then
Eject_maju = 1
Else
If Ls_eject_maju = 1 Then
Eject_maju = 0
Else
If Ls_eject_maju = 1 Then
Eject_mundur = 1
Else
If Ls_eject_mundur = 1 Then
Eject_mundur = 0
End If
End If
End If
End If

Print “Pause_time”
Waitms 340

Goto 20
End

End ‘end program

George Simon Ohm (1787-1854)

Georg Simon Ohm was a German physicist born in Erlangen, Bavaria, on March 16, 1787. As a high school teacher, Ohm started his research with the recently invented electrochemical cell, invented by Italian Count Alessandro Volta. Using equipment of his own creation, Ohm determined that the current that flows through a wire is proportional to its cross sectional area and inversely proportional to its length or Ohm’s law.

George Simon Ohm adalah seorang fisikawan jerman yang lahir di Erlangen, Bavaria pada tanggal 16-maret-1787. Dia hanyalah seorang guru SMA yang memulai risetnya saat teknik Electrochemical Cell ditemukan oleh Alessandro Volta dari Italia.

Using the results of his experiments, Georg Simon Ohm was able to define the fundamental relationship between voltage, current, and resistance. These fundamental relationships are of such great importance, that they represent the true beginning of electrical circuit analysis.

Dari hasil eksperimennya George Simon Ohm menemukan hubungan dasar antara Tegangan, Arus dan Resistansi. Hubungan dasar ini menjadi sangat penting dan menjadi cikal bakal semua acuan untuk menganalisa sirkuit listrik sampai masa kini.

Unfortunately, when Ohm published his finding in 1827, his ideas were dismissed by his colleagues. Ohm was forced to resign from his high-school teaching position and he lived in poverty and shame until he accepted a position at Nüremberg in 1833 and although this gave him the title of professor, it was still not the university post for which he had strived all his life.

Sayangnya, pada saat dia mengumumkan penemuan itu di tahun 1827, ide itu dicekal oleh para koleganya. Dengan tidak mengenal putus asa dan rasa malu George tetap mengajar di kelasnya dan hidup dalam tekanan ekonomi sampai akhirnya idenya diterima di Nuremberg pada tahun 1833 hingga mendapat gelar profesor. Yang patut diteladani walau gelarnya tinggi ia tetap bersahaja tidak sok ilmuwan dan terus berjuang sepanjang hayatnya.

Ohm the Genius! the Mozart of Electricity …

Ohm and corrosion monitoring

Ohm’s main interest was current electricity, which had recently been advanced by Alessandro Volta’s invention of the battery. Ohm made only a modest living and as a result his experimental equipment was primitive. Despite this, he made his own metal wire, producing a range of thickness and lengths of remarkable consistent quality. The nine years he spent at the Jesuit’s college, he did considerable experimental research on the nature of electric circuits. He took considerable pains to be brutally accurate with every detail of his work. In 1827, he was able to show from his experiments that there was a simple relationship between resistance, current and voltage.

Ohm’s sangat tertarik menyelidiki arus listrik setelah Alessandro Volta menemukan battery. Dalam penyelidikan itu Ohm mempergunakan alat-alat sederhana dan kuno namun dalam teknik pembuatanya ia memperhatikan kualitas secara presisi seperti kawat metal buatannya. Setelah menghabiskan pendidikannya di perguruan tinggi Jesuit’s, Ohm lebih amat sangat teliti dalam semua pekerjaannya. Pada tahun 1827 barulah ia berani mempertunjukan hubungan sederhana antara resistance, arus dan tegangan.

Ohm’s law stated that the amount of steady current through a material is directly proportional to the voltage across the material, for some fixed temperature:

Ohms menyatakan bahwa arus yang mengalir melalui suatu bahan adalah sepadan dengan tegangan yang melintasi bahan itu. Dinyatakan dalam rumus yang terkenal :

I = V/R

Ohm had discovered the distribution of electromotive force in an electrical circuit, and had established a definite relationship connecting resistance, electromotive force and current strength.

Kemudian Ohms menemukan distribusi dari gaya elektromotif dalam rangkaian listrik yang menentukan hubungan pasti terhadap rangkaian resistance, gaya electromotive dan kuat arusnya.

Ohm was afraid that the purely experimental basis of his work would undermine the importance of his discovery. He tried to state his law theoretically but his rambling mathematically proofs made him an object of ridicule. In the years that followed, Ohm lived in poverty, tutoring privately in Berlin. He would receive no credit for his findings until he was made director of the Polytechnic School of Nüremberg in 1833. In 1841, the Royal Society in London recognized the significance of his discovery and awarded him the Copley medal. The following year, they admitted him as a member. In 1849, just 5 years before his death, Ohm’s lifelong dream was realized when he was given a professorship of Experimental Physics at the University of Munich. On July 7th,1854 he passed away in Munich, at the age of 65.

Hampir-hampir ia ragu bahwa hasi teori dasarnya gugur dan menjadi bahan olok-olokan karena selama itu kemiskinan selalu menderanya hingga ia tetap mengajar secara privat di Berlin. Karena itulah hasil penemuannya tidak pernah mendapat simpati dan pengakuan sampai pada akhirnya menjadi pucuk pimpinan di sekolah polyteknik Nuremberg pada tahun 1833. Di tahun 1849, lima tahun sebelum wafat, mimpi panjangnya menjadi kenyataan saat menjadi guru besar di Experimental Physics, the University of Munich. Ohm wafat di usia 65 tahun, tepatnya 7-Juli-1854.

This belated recognition was welcome but there remains the question of why someone who today is a household name for his important contribution struggled for so long to gain acknowledgement. This may have no simple explanation but rather be the result of a number of different contributory factors. One factor may have been the inwardness of Ohm’s character while another was certainly his mathematical approach to topics which at that time were studied in his country a non-mathematical way. There was undoubtedly also personal disputes with the men in power which did Ohm no good at all. He certainly did not find favor with Johannes Schultz who was an influential figure in the ministry of education in Berlin, and with Georg Friedrich Pohl, a professor of physics in that city.

Pengakuan teori ohm terlambat namun kematiannya membekaskan pertanyaan : mengapa perjuangan panjang beliau sangat berat dan panjang untuk mendapat pengakuan setelah kematiannya, padahal penemuan (yang dianggap) sepele itu ikut ambil bagian terbesar dalam peralatan rumah tangga kita?. Ini membutuhkan penjelasan panjang dan banyak penyebab. Salah satu faktornya mungkin pembahasan teorinya dengan pendekatan matematis yang rumit sedangkan latar belakang sekolahnya dianggap tidak mendukung apa yang digagaskannya. Pada saat itu banyak orang meragukan bahwa teorinya hanya bualan semata!. Pada saat itu sayangnya ia tidak mengenal kebaikan hati orang yang berpengaruh seperti Johannes Schultz sebagai menteri pendidikan di Berlin dan Friedrich Pohl, seorang professor fisika di kotanya.

Electricity was not the only topic on which Ohm undertook research, and not the only topic in which he ended up in controversy. In 1843 he stated the fundamental principle of physiological acoustics, concerned with the way in which one hears combination tones. However the assumptions which he made in his mathematical derivation were not totally justified and this resulted in a bitter dispute with the physicist August Seebeck. He succeeded in discrediting Ohm’s hypothesis and Ohm had to acknowledge his error.

Padahal bidang kelistrikan bukanlah topic utama Ohm dalam semua risetnya dan bukanlah perjalanan kontroversi satu-satunya dalam penemuannya. Di tahun 1843 bahkan ia menyatakan prinsip dasar psikologi akustik yang menyelidiki respon pendengaran manusia terhadap kombinasi nada. Lagi-lagi dengan asumsi bahwa Ohm bukan Ilmuwan dan pakar matematika handal, ia menuai hinaan yang menyakitkan dari fisikawan August Seebeck, dalam perdebatan, Seebeck telah berhasil meruntuhkan hipotesa Ohm salah besar!. He..he…he…dia keliru besar.

Pesan dan kesan : bahwa tidak semua penemuan besar lahir dari disiplin bidang keilmuan yang sama. Perjuangan yang panjang dengan kesabaran dan disiplin tinggi dapat mencapai hasil yang bermanfaat bagi umat manusia. Jangan pernah meremehkan pendapat orang lain karena latar belakangnya atau kemiskinannya.

Salam : Yonni.

Bottom of Form

]]> http://yonni1967.wordpress.com/2008/10/05/george-simon-ohm/feed/ 0 yonni1967 ohm-poto1 http://yonni1967.wordpress.com/2008/10/02/power-amplifier-tutorial/ http://yonni1967.wordpress.com/2008/10/02/power-amplifier-tutorial/#comments Thu, 02 Oct 2008 14:19:52 +0000 yonni1967 http://yonni1967.wordpress.com/?p=164 ]]> Understanding amplifier power ratings

(pemahaman rating power amplifier)

There are different methods for measuring the power ratings for amplifiers and speakers. And different measuring methods give different values so it is vital to understand the difference between theosedifferent power ratings to be able to make at least some comaparision between different power ratings. This article is collection of information posted to rec.audio.tech newsgroup at July 1996. The information is compiled from Usenet newsgroup rec.audio.pro articles written by Norbert Hahn, Dick Pierce and Earl K.

Ada beberapa cara berbeda untuk mengukur nilai power amplifier dan speaker. Cara pengukuran ini memberikan pandangan sangat berbeda dan penting untuk memahami perbedaan antara theosedifferent power rating yang membuat perbedaan comparision power rating. Artikel ini koleksi dari posting rec.audio.tech newsgroup pada bulan Juli 1996. Informasi di-compile dari Usenet newsgroup rec.audio.pro dan ditulis oleh Norbert Hahn, Dick pierce dan Earl K.

RMS power

(Apa sih RMS itu ?)

To make it short, an RMS power value is directly related to perceivable energy (acoustical, heat, light – or what else applies).

Arti harfiahnya ialah : RMS adalah suatu nilai tenaga (power) yang secara langsung dihubungkan dengan energi yang dapat dipahami (akustik, panas, cahaya atau sejenisnya).

“RMS” is really a rather meaningless figure, when measuring power. R.M.S. is useful for measuring the “power-producing equivalent” voltage. Thus 10 Volts RMS will produce the same power into a given impedance that 10 Volts DC would produce (onto a resistance) Any waveform of 10 V R.M.S.will produce the same power into that impedance. This is because it’s the root of the mean of all the average squared voltages to which Norbert Hahn referred in the prior post. It is if little meaning to compute the mean of squares of all the power values in a wave.

” RMS” sebenarnya suatu figur yang tidak penting saat mengukur power. R.M.S. bermanfaat untuk mengukur ” power-producing (yang sepadan)” dengan voltase. Dengan umpan 10 VOLT RMS akan menghasilkan sama ke dalam impedansi yang ditentukan dan akan menghasilkan 10 VOLT DC ( dalam resistansi) semua bentuk gelombang apapun dari 10 V R.M.S. Ini adalah musabab akar dari semua rata-rata dalam tegangan seperti yang direferensikan oleh Norbert Hahn di postingnya. Pemahaman ini lebih sedikit dibanding perhitungan mean of square ( nilai akar rata-rata) pada segala nilai dan bentuk gelombang.

RMS, when applied to power measurements, has come to mean “sine-wave power.” A 100 Watt “RMS” amplifier can produce a 100 Watt sine-wave into its load. With music, the total actual power would be less. With a square-wave, it would be more.

RMS, saat pengukuran power mempunyai arti ” sine-wave power“. Amplifier 100 Watt ” RMS” berarti menghasilkan tenaga 100 Watt sine-wave ke dalam bebannya. Dengan dibebani musik, total power nyatanya, ternyata berkurang. Dengan mengumpanii square-wave maka akan lebih meningkat. Mengapa demikian?.

DIN power

The DIN 45000 defines different methods to measure power, depending on the device under test. Well, this is what I remember from reading the DIN some 25 years ago.

For home applicances there are three different numbers for power: Continous power, Peak power and power bandwidth; the latter does not apply for speakers.

DIN 45000 menggambarkan metoda lain untuk mengukur power, tergantung alat testernya, ini yang harus diingat saat mempelajari DIN yang berlaku 25 tahun lampau.

Untuk peralatan rumah tangga ada tiga perbedaan pokok tentang normalisasi power yaitu : continous power, Peak Power dan power bandwidth. Yang terakhir tidak diaplikasikan pada speaker.

Power measurement of an amp requires that the amp is properly terminated by Ohmic resistances of nominal value both at input and output. The continous power is measured when the amp is supplied by its normal power supply. It must then be able to deliver the rated power at 1 kHz for at least 10 minutes while the maximum THD does not exceed 1 %. To measure the peak power the normal power supply is replaced by a regulated power supply and the time for delivering the power is reduced. Thus, higher values for peak power are obtained. You may skip measuring the peak power by simply multiplying the continuous power by 1.1.

Pengukuran amplifier memerlukan nilai hambatan Ohmic dari nilai nominal kedua- masukan dan keluaran. Continous power diukur ketika amp disuplai oleh normal power supply. Kemudian bisa mengirim power rating power 1 kHz sedikitnya 10 menit saat maksimum THD tidak melebihi 1%. Untuk mengukur daya puncak power yang normal digantikan oleh penggunaan power supply yang terserap olehnya. Seperti itulah nilai tertinggi untuk daya puncak dapat diperoleh. Kita boleh mengabaikan pengukuran daya puncak dengan hanya mengalikan continous power dengan perkalian : 1×1.

The power bandwidth is defined as the bw for which 1/2 of the rated continous power can be obtained.

Actually, DIN 45 500, CNF 97-330, EIA RS-426 and the encompassing IEC 268-5 specify not pink noise, but pink noise filtered by a filter that provides sinificant attenuation in the low and high frequency region of the spectrum to more closely model the long-term spectral distribution of music. Pink noise itself does not accomplish this

Power bandwitdh digambarkan sebagai bw di mana 1/2 dari rating continous power dapat diperoleh.

Sebenarnya , DIN 45 500, CNF 97-330, EIA RS-426 yang mencakup IEC 268-5 tidak menspesifikasikan bising merah muda (Pink noise), tetapi bising merah muda yang disaring oleh suatu penekanan penyaringan yang sinificant di daerah frekwensi tinggi dari rendah dari spektrum kepada mode long term spectral distribusi musik. Pink noise sendiri tidak memenuhi kriteria ini

PMPO (Peak Music Power)

So called “music power”. This power figure tells the power which the amplifier can maximally supply in some conditions. PMPO rating gives the highest measuring value, but this info is quite useless, because there is no exact standard how PMPO power should be measured.

Sekarang lagi trend orang menyebut : ” music power “. Sebenarnya figure ‘power’ tersebut berusaha menjelaskan pada kondisi yang mana amplifier dapat secara maksimal menyediakan sumber tenaga. Rating PMPO maksudnya memberi nilai pengukuran maksimum, tetapi informasi ini sebenarnya tidak relevan sebab tidak ada standard yang tepat bagaimana power PMPO terukur.

The reason for this power rating was to show the max capability of equippment for recreating strong musical tansients like kettle drums and the like. Similar thing (music power rating) was used in the sixties, and I think it assumed a square wave that swung the whole supply range of the output stage. This alone gives them a factor of two over a clean sine wave note.

Alasan power rating maksimum ini adalah hanya menunjukkan kemampuan maximum equipment untuk melukiskan kekuatan transient dalam hal musical seperti dentuman perkusi Drums yang digunakan sejak tahun 60 an. Asumsinya adalah ada sebuah gelombang persegi yang mengayun pada jangkah suplai terhadap tingkatan output yang memberikan satu factor terhadap dua sinyal over pada sebuah gelombang sinus bersih yang lewat.

But the ugliest thing they did was to assume that the high power lasted such a short period of time that the power supply caps would hold the voltages steady without any drooping. In the real world, an under powered PS could be hidden by this ruse and the PMPO might be a factor of 10 or more higher than what could be sustained on a nice instrumental performance.

Tetapi hal paling buruk bagi asumsi ini adalah bahwa kualitas high power seperti layaknya perioda pendek kemampuan power suplly untuk menahan stabilitas tegangan tanpa adanya droping diabaikan. Pada kenyataannya penampilan PSU untuk mengatasi masalah perhitungan PMPO ini harus memperhitungkan factor 10 tiap power rating ditingkatkan volumenya yang tentunya mempengaruhi penampilan kualitas musik.

Forget what adverts say about peak power or other “power terms” because they are not standardized and anyway comparable between equipments. Just look for “RMS continuous Power” or other reliable power rating (like DIN power).

Maka dari itu mari kita lupakan perdebatan sengit tentang terminology ‘Peak power’ (istilah itu hanya salah kaprah dan umum) yang sebenarnya tidak ada standarisasi yang cocok diterapkan di banyak equipment. Kita hanya mereferensikan “RMS continous power” atau badan standarisasi yang dapat dipercaya seperti DIN power.

Speaker power ratings

The nominal power for speakers is defined quite differently: The continous power is measured by pink noise rather than a sinousoidal signal and it is applied for 24 hours. Bandwidth of the noise is as required/specified by the speaker. Thus the nominal power is applicable to both a single chassis/driver and complete box.

Perhitungan nominal power untuk speaker dapat dijelaskan dengan jalan: Continous power diukur dengan generator pink noise berbanding dengan sinyal sinus yang diaplikasikan selama 24 jam penuh. Lebar bidang noise harus sesuai dengan spesifikasi speaker. Kemudian nilai nominal powernya dapat dilaksanakan dengan driver dan desain boxnya.

And the THD is not the limiting factor: It is replaced by the term that the speaker should by no means be damaged. Rhe requirement is that the speaker meet the manufacturers performance sapecification after the power cycle.

The maximum power is defined for woofers and boxes only. It is measured by applying sinusoidal signals of 250 Hz and lower such that the speaker is neither damaged nor produces unwanted output.

THD tidak membatasi limiting factor dengan terminology bahwa sampai dimana kesanggupan speaker menampung daya dan tidak sampai rusak. Tentu harus dipelajari spesifikasi pabrik pembuat speaker sebelum pengujian.

The AES/ANSI spec provides for two power measurements: thermal power, as you describe above, and excursion limiting, which is determined by either the hard mechanical limits afforded by the suspension, or the difference between the length of the voice coil and the length of the magnetic gap.

Spec. AES/ANSI telah mengembangkan dua tolok ukur pengukuran cermat lain : Thermal power seperti yang disebutkan di atas dan pembatasanya dimana ada pendekatan hal lain seperti (melihat dulu) mekanikal speaker pada kelenturan suspensi speaker atau jarak antara voice coil dan jarak celah magnet speaker.

Other amplifier specifications

Speaker impedance the amplifier is designed to drive

Many amps manufactured these days are rated only for 8-ohm-and-above loads, and not for 4-ohm loads. This is done largely as a cost savings by the manufacturer. Amps which are capable of driving 4-ohm loads to the same output voltage require heftier power supplies, heatsinks, and (often) output-stage transistors: they’ll be delivering twice as much current into the load, and will be dissipating roughly twice as much heat within their output stages.

Kini banyak pembuat amplifier menyediakan rating beban speaker sebesar 8 ohms dan bukannya 4 ohms. Maksud dari semua ini adalah dengan alasan menghemat daya power suplly dan keping pendingin pada transistor akhir dimana semakin besar dayanya semakin besar pula disipasi daya yang terhambur pada finalnya.

If a manufacturer chooses to quote a power rating at 4 ohms in their advertising, the amp must be capable of delivering this much power after a ‘warmup’ period of operation at 1/3 power (which level actually dissipates _more_ heat in the output stage than full-power operation).

Jika ada pabrikan mengklaim power buatanya berating sanggup mengatasi beban pada 4 ohms, amplifier buatannya harus mampu mensuplai banyak tenaga selama “warm up” period untuk pengoperasian pada 1/3 tenaga yang mana dilevel itu sudah banyak pemborosan daya yang memancar sebagai panas selama pengoperasian penuh!. Kesimpulanya beban impedansi 4 ohm bukan alasan untuk mendongkrak performance amplifier.

In order to save money during manufacture, manufacturers often use skimpier power supplies, heatsinks, and output stages – and as a result, the amps may have a 4-ohm power rating which is _less_ than the 8-ohm rating. This is somewhat embarrassing for the manufacturer to advertise – and, so, they often do not quote a 4-ohm power rating at all, and state that the amp is designed to be used only with loads of 8 ohms or above.

Untuk mengatasi hal itu dibutuhkan desain yang menelan biaya mahal. Pembuat amplifier biasanya mengatasinya dengan “skimpier” power supply, keping pendingin lebih tebal dan lapis multi final pada outputnya dibanding desain 8 ohms. Padahal desain-desain itu lebih aman beroperasi pada beban 8 ohm ke atas.

With many such amplifiers, you can drive a 4-ohm load safely, as long as you don’t try to drive it too hard. If you drive a low-Z load to too high a volume, one of several things may happen: the amp may begin to “clip” (sounds very harsh and distorted, may damage the tweeters), or may overheat and shut itself down, or may overheat and burn up (all the magic blue smoke leaks out).

Memang ada beberapa amplifier yang aman beroperasi pada beban 4 ohm, hanya harus diingat jangan terlampau keras memperkosanya dengan volume tinggi dan dengan dentuman bass yang menggebu-gebu!. Ingat! Akan terjadi “clipping” yaitu suara tersendat atau cacat dan dapat membakar coil tweeter dalam sekejab!. Bahaya yang lain yaitu terjadi kebakaran dan pijaran api biru pada peralatan.

Methods for making 4 ohm speaker to appear as 8 ohm

cara membikin speaker 4 ohm menjadi 8 ohm

• Wire a 4-ohm power resistor (10-20 watt) in series with each 4-ohm speaker. This makes the system to be appear as 8 ohm load and is inexpensive. The cons are that the resistor wastes power, may cause frequency response go bad because speakers do not have constant resistance with frequency. When you play at high volumes the resistor may get hot and burn thing or itself.

• Pasang resistor 4 ohm 10-20 watt seri dengan coil speaker. Resistor ini sebagai ballast tapi resikonya memotong bandwidth. Respon frekuensinya jelek dan jangan pasang volume keras-keras karena resistor ini akan terbakar.

• Using 4 ohm to 8 ohm matching transformer will not waste much power, but the transformer will be heavy, expensive and hard to find. Transformer has also problems in playing back lowest frequencies (saturation causes distortion in high levels) and in higher frequencies the inductance in the transformer will cause phase shifts.

• Memakai trafo penyesuai jauh lebih baik hanya ukurannya menjadi berat dan mahal. Resiko yang lain adalah respon pada frekuensi rendah terjadi saturasi yang menyebabkan distorsi. Pada frekuensi tinggi induktansi trafo menyebabkan pergeseran fasa.

• You can wire two 4-ohm speakers in series if you have two identical speakers. Problem is that if the speakers are not identical type the frequency response and power distributin will be uneven.

• Cara yang lebih baik lagi adalah menyeri dua buah speaker yang identik. Hanya saja “identik” disini sangat sukar ditemukan walau sama persis secara fisik, harus betul-betul eksak dan absolute.

• Most “8-ohm” amplifiers can drive a 4-ohm or 6-ohm load as long as you don’t try to get full power out of the amp (if you do, it may overheat and shut down).

• Banyak amplifier 8 ohm dapat beroperasi baik pada 4 atau 6 ohm selama anda suka, namun ingat sekali lagi jangan diperkosa beroperasi penuh pada volume tinggi jika tidak ingin terbakar!.

• Buy yourself a decent power amplifier whose output stage and power supply are capable of handling a real honest low-impedance load. Good amplifier will be expensive but gives best sound quality and reliabity.

• Solusi terakhir jika anda pengidam power ukuran besar; belilah amplifier desain khusus dengan rating power yang sanggup beroperasi pada impedans rendah (tapi mahal dan sulit dapatnya), dijamin memang akan memberikan performa bagus dan memuaskan.

Dampling factor

The output impedance of an amp should be extremely low. If it’s .8 Ohms, then an 8-Ohm speaker has a damping factor of 10. If it’s .08, then the amplifier provides a damping factor of 100, etc. Don’t confuse the actual output (source) impedance with the load impedance that is recommended for the amp (4-Ohms, 8-Ohms, etc).

Impedansi keluaran amplifier bisa jadi rendah sekali. Jika amplifier 8 ohm diumpankan pada speaker 8 ohm memiliki damping factor 10, jika .08 ohm maka dampling faktornya 100 dan seterusnya. Jangan dicampur adukkan antara actual output (sumber) impedansi dengan beban impedansi yang direkomendasikan amplifier 4 ohm, 8 ohm dan seterusnya.

The idea is that if the speaker is 8 Ohms, and the amplifier has a source impedance of .08 Ohms, then the amplifier “damps” the motion of the cone by a “factor” of 100. In reality, the true damping that the cone “sees” is determined by many things, part of which is the damping limitation imposed by the resistance of the voice coil, usually around 5 Ohms or so for an 8-Ohm speaker. You can see that if the speaker has 5 Ohms of resistance, the internal (source) impedance of the amplifier (.08 Ohms for a damping factor of only 100) doesn’t add much to the total resistance in the voice coil circuit, hence has very little effect on total damping. So any modest change in the amplifier damping factor correlates to virtually no change in total damping.

Idealnya speaker 8 ohm itu diumpankan pada sumber impedansi amplifier .08 ohm dimana terjadi peredaman gerakan konus speaker berdasarkan atas factor 100. pada kenyataannya peredaman konus terlihat dalam beberapa hal : misalnya batas resistansi koil speaker, biasanya sekitar 5 ohm atau lebih untuk speaker 8 ohm. Coba anda ukur dengan multi tester harga tahanannya pasti sekitar 5 ohm! Ingat : untuk .08 ohm factor damping nya hanya 100!. Maka dari itu jangan menambahkan harga total resistansi koil suara.

A speaker designer shoots for a certain damping (same as 1/Q) to achieve a certain desired type of low-frequency rolloff. The assumption is that the source impedance of the amplifier is 0 Ohms. If the source impedance is .08 Ohms (damping factor of 100), very little error is introduced into the system. Higher damping factors are getting into diminishing returns in terms of the total damping. In practice we want a certain, relatively low damping figure for the whole speaker system, (1.414 for a maximally flat bass response).

Pendesain speaker menetapkan damping sebagai 1/Q untuk untuk menggambarkan type dari roll-off frekuensi rendah dengan anggapan bahwa sumber impedansi amplifier adalah 0 ohm. Jika sumber impedansi .08 ohm dan faktornya 100 akan terjadi sedikit error pada system. Damping factor yang terlalu tinggi akan mengurangi harga terhadap total dampening faktornya. Dalam prakteknya kita selalu mengidamkan suara merdu bass flat respon secara maksimal.

What is amplifier “bridging” or “monoblocking”?

When you’re told a stereo power amplifier can be bridged, that means that it has a provision (by some internal or external switch or jumper) to use its two channels together to make one mono amplifier with 3 to 4 times the power of each channel. This is also called “Monoblocking” and “Mono Bridging”.

Jika anda bilang : stereo amplifier dapat dijembatankan sebanyak 3 atau 4 lapis per chanel bersama maka hal itu lazim disebut sebagai “mono blocking” atau “mono bridging”

Bridging typical HIFI amplifier involves connecting one side of the speaker to the output of one channel and the other side of the speaker to the output of the other channel. The channels are then configured to deliver the same output signal, but with one output the inverse of the other. The beauty of bridging is that it can apply twice the voltage to the speaker. Since power is equal to voltage squared divided by speaker impedance, combining two amplifiers into one can give four (not two) times the power.

Tipikalnya adalah menggabungkan dua buah amplifier per chanel sekaligus pada satu speaker. Dua buah amplifier itu mengirimkan sinyal bersama tapi lain fasanya/saling menjungkir. Akal-akalan itu memang dapat diperoleh dua kali lipat tegangan pada satu speaker. Awalnya anggapanya diperoleh harga tegangan 4 kali lipat!

In practice, you don’t always get 4 times as much power. This is because driving bridging makes one 8 ohm speaker appear like two 4 ohm speakers, one per channel. In other words, when you bridge, you get twice the voltage on the speaker, so the speakers draw twice the current from the amp.

Sekali lagi dijelaskan disini penggabungan 2 buah amplifier menghasilkan dua kali tegangan dan arus pada speaker bukan 4 kali!. Logikanya pengendalian speaker 8 ohm akan ditampilkan sebagai 4 ohm speaker. Jadi akan mendongkrak daya.

Another interesting consequence of bridging is that the amplifier damping factor is cut in half when you bridge. Generally, if you use an 8 ohm speaker, and the amplifier is a good amp for driving 4 ohm speakers, it will behave well bridging.

Jika anda tertarik menggunakan metoda ini konsekwensinya damping factor akan memotong setengah gelombang sinyal. Jadi harus diperhatikan : metoda ini bagus jika : anda pasang speaker 8 ohm dengan desain amplifier khusus bridge 4 ohm speaker.

Also consider amplifier output protection. Amps with simple power supply rail fusing are best for bridging. Amps that rely on output current limiting circuits to limit output current are likely to activate prematurely in bridge mode, and virtually every current limit circuit adds significant distortion when it kicks in. Remember bridging makes an 8 ohm load look like 4 ohms, a 4 ohm load look like 2 ohms, etc.

Pergunakanlah pengaman speaker karena masalah metoda ini pada pembatasan arus sirkuit terhadap arus keluaran dan pembatasan sirkuit arus semu yang ikut andil dalam hal distorsi bila konus terdorong sinyal. Ingat! Metoda ini membuat beban 8 ohm terlihat sebagai 4 ohm, 4 ohm terlihat sebagai 2 ohm dan seterusnya.

]]> http://yonni1967.wordpress.com/2008/10/02/power-amplifier-tutorial/feed/ 1 yonni1967 pioneer_sa-608_integrated_amplifier_web_small http://yonni1967.wordpress.com/2008/10/02/operating-system/ http://yonni1967.wordpress.com/2008/10/02/operating-system/#comments Thu, 02 Oct 2008 13:58:26 +0000 yonni1967 http://yonni1967.wordpress.com/?p=156 ]]> Bagi teman-teman pelajar, mahasiswa dan umum yang mengikuti program study dan pendalaman materi Operating System dapat mendown load file berikut ini yaitu mengenai sistim operasi : Windows, Unix dan Linux dalam versi format PDF.

For students and publics who’s concerning program in Operating System easy download this following items of the file operation systems lecture notes like : Windows, Unix and Linux in PDF format.

sisitem-operasi

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Surabaya A	Jl. Manyar Kertoarjo No. 1	031 596 1512-6
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Berikut data yang dapat saya sampaikan untuk dipergunakan dengan baik dan benar.

In electrical engineering and industry, thermocouples are a widely used type of temperature sensor and can also be used as a means to convert thermal potential difference into electric potential difference.They are cheap and interchangeable, have standard connectors, and can measure a wide range of temperatures. The main limitation is accuracy; System errors of less than one degree Celsius (°C) can be difficult to achieve

History

In 1821, the German–Estonian physicist Thomas Johann Seebeck discovered that when any conductor (such as a metal) is subjected to a thermal gradient, it will generate a voltage. This is now known as the thermoelectric effect or Seebeck effect. Any attempt to measure this voltage necessarily involves connecting another conductor to the “hot” end. This additional conductor will then also experience the temperature gradient, and develop a voltage of its own which will oppose the original. Fortunately, the magnitude of the effect depends on the metal in use. Using a dissimilar metal to complete the circuit creates a circuit in which the two legs generate different voltages, leaving a small difference in voltage available for measurement. That difference increases with temperature, and can typically be between 1 and 70 microvolts per degree Celsius (µV/°C) for the modern range of available metal combinations. Certain combinations have become popular as industry standards, driven by cost, availability, convenience, melting point, chemical properties, stability, and output. This coupling of two metals gives the thermocouple its name.

Thermocouples measure the temperature difference between two points, not absolute temperature. In traditional applications, one of the junctions—the cold junction—was maintained at a known (reference) temperature, while the other end was attached to a probe.

Having available a known temperature cold junction, while useful for laboratory calibrations, is simply not convenient for most directly connected indicating and control instruments. They incorporate into their circuits an artificial cold junction using some other thermally sensitive device, such as a thermistor or diode, to measure the temperature of the input connections at the instrument, with special care being taken to minimize any temperature gradient between terminals. Hence, the voltage from a known cold junction can be simulated, and the appropriate correction applied. This is known as cold junction compensation.

Additionally, a device can perform cold junction compensation by computation. It can translate device voltages to temperatures by either of two methods. It can use values from look-up tables or approximate using polynomial interpolation.

A thermocouple can produce current, which means it can be used to drive some processes directly, without the need for extra circuitry and power sources. For example, the power from a thermocouple can activate a valve when a temperature difference arises. The electric power generated by a thermocouple is a conversion of the heat energy that one must continuously supply to the hot side of the thermocouple to maintain the electric potential. The flow of heat is necessary because the current flowing through the thermocouple tends to cause the hot side to cool down and the cold side to heat up (the Peltier effect).

Thermocouples can be connected in series with each other to form a thermopile, where all the hot junctions are exposed to the higher temperature and all the cold junctions to a lower temperature. The voltages of the individual thermocouples add up, allowing for a larger voltage and increased power output, thus increasing the sensitivity of the instrumentation. With the radioactive decay of transuranic elements providing a heat source this arrangement has been used to power spacecraft on missions too far from the Sun to utilize solar power.

Thermocouple materials are available in several different metallurgical formulations per type, such as: (listed in decreasing levels of accuracy and cost) Special limits of error, Standard, and Extension grades. Extension grade wire is less costly than dedicated thermocouple junction wire and it’s usually specified for accuracy over a more restricted temperature range. Extension grade wire is used when the point of measurement is farther from the measuring instrument than would be financially viable for standard or special limits materials, and has a very similar thermal coefficient of EMF for a narrow range (usually encompassing ambient). In this case, a standard or special limits wire junction is tied to the extension grade wire outside of the area of temperature measurement for transit to the instrument. Since most modern temperature measuring instruments that utilize thermocouples are electronically buffered to prevent any significant current draw from the thermocouple, the length of the thermocouple or extension wire is irrelevant.

Changes in metallurgy along the length of the thermocouple (such as termination strips or changes in thermocouple type wire) will introduce another thermocouple junction which affects measurement accuracy. Also, in the United States, industry standards are that the thermocouple color code is used for the insulation of the positive lead, and red is the negative lead.

Types…………:

A variety of thermocouples are available, suitable for different measuring applications. They are usually selected based on the temperature range and sensitivity needed. Thermocouples with low sensitivities (B, R, and S types) have correspondingly lower resolutions. Other selection criteria include the inertness of the thermocouple material, and whether or not it is magnetic. The thermocouple types are listed below with the positive electrode first, followed by the negative electrode.

Type K (chromel–alumel) is the most commonly used general purpose thermocouple. It is inexpensive and, owing to its popularity, available in a wide variety of probes. They are available in the −200 °C to +1350 °C range. The type K was specified at a time when metallurgy was less advanced than it is today and, consequently, characteristics vary considerably between examples. Another potential problem arises in some situations since one of the constituent metals, nickel, is magnetic. One characteristic of thermocouples made with magnetic material is that they undergo a step change when the magnetic material reaches its Curie point. This occurs for this thermocouple at 354°C. Sensitivity is approximately 41 µV/°C.

Type E

Type E (chromel–constantan) has a high output (68 µV/°C) which makes it well suited to cryogenic use. Additionally, it is non-magnetic.

Type J

Type J (iron–constantan) is less popular than type K due to its limited range (−40 to +750 °C). The main application is with old equipment that cannot accept modern thermocouples. J types cannot be used above 760 °C as an abrupt magnetic transformation causes permanent decalibration. The magnetic properties also prevent use in some applications. Type J thermocouples have a sensitivity of about 50 µV/°C.

Type N

Type N (nicrosil–nisil) thermocouples are suitable for use at high temperatures, exceeding 1200 °C, due to their stability and ability to resist high temperature oxidation. Sensitivity is about 39 µV/°C at 900°C, slightly lower than type K. Designed to be an improved type K, it is becoming more popular.

Type B, R, and S

Types B, R, and S thermocouples use platinum or a platinum–rhodium alloy for each conductor. These are among the most stable thermocouples, but have lower sensitivity, approximately 10 µV/°C, than other types. The high cost of these makes them unsuitable for general use. Generally, type B, R, and S thermocouples are used only for high temperature measurements.

Type B thermocouples use a platinum–rhodium alloy for each conductor. One conductor contains 30% rhodium while the other conductor contains 6% rhodium. These thermocouples are suited for use at up to 1800 °C. Type B thermocouples produce the same output at 0 °C and 42 °C, limiting their use below about 50 °C.

Type R thermocouples use a platinum–rhodium alloy containing 13% rhodium for one conductor and pure platinum for the other conductor. Type R thermocouples are used up to 1600 °C.

Type S thermocouples use a platinum–rhodium alloy containing 10% rhodium for one conductor and pure platinum for the other conductor. Like type R, type S thermocouples are used up to 1600 °C. In particular, type S is used as the standard of calibration for the melting point of gold (1064.43 °C).

Type T

Type T (copper–constantan) thermocouples are suited for measurements in the −200 to 350 °C range. Often used as a differential measurement since only copper wire touches the probes. As both conductors are non-magnetic, type T thermocouples are a popular choice for applications such as electrical generators which contain strong magnetic fields. Type T thermocouples have a sensitivity of about 43 µV/°C.

Type C

Type C (tungsten 5% rhenium – tungsten 26% rhenium) thermocouples are suited for measurements in the 0 °C to 2320 °C range. This thermocouple is well-suited for vacuum furnaces at extremely high temperatures and must never be used in the presence of oxygen at temperatures above 260 °C.

Type M

Type M thermocouples use a nickel alloy for each wire. The positive wire contains 18% molybdenum while the negative wire contains 0.8% cobalt.These thermocouples are used in the vacuum furnaces for the same reasons as with type C. Upper temperature is limited to 1400 °C. Though it is a less common type of thermocouple, look-up tables to correlate temperature to EMF (milli-volt output) are available.

Type Chromel-gold/iron

In chromel-gold/iron thermocouples, the positive wire is chromel and the negative wire is gold with a small fraction (0.03–0.15 atom percent) of iron. It can be used for cryogenic applications (1.2–300 K and even up to 600 K). Both the sensitivity and the temperature range depends on the iron concentration. The sensitivity is typically around 15 µV/K at low temperatures and the lowest usable temperature varies between 1.2 and 4.2 K.

Thermocouple comparison

The table below describes properties of several different thermocouple types. Within the tolerance columns, T represents the temperature of the hot junction, in degrees Celsius. For example, a thermocouple with a tolerance of ±0.0025×T would have a tolerance of ±2.5 °C at 1000 °C.

Applications

Thermocouples are most suitable for measuring over a large temperature range, up to 1800 °C. They are less suitable for applications where smaller temperature differences need to be measured with high accuracy, for example the range 0–100 °C with 0.1 °C accuracy. For such applications, thermistors and resistance temperature detectors are more suitable.

Steel industry

Type B, S, R and K thermocouples are used extensively in the steel and iron industries to monitor temperatures and chemistry throughout the steel making process. Disposable, immersible, type S thermocouples are regularly used in the electric arc furnace process to accurately measure the steel’s temperature before tapping. The cooling curve of a small steel sample can be analyzed and used to estimate the carbon content of molten steel.

Heating appliance safety

Many gas-fed heating appliances such as ovens and water heaters make use of a pilot light to ignite the main gas burner as required. If the pilot light becomes extinguished for any reason, there is the potential for un-combusted gas to be released into the surrounding area, thereby creating both risk of fire and a health hazard. To prevent such a danger, some appliances use a thermocouple as a fail-safe control to sense when the pilot light is burning. The tip of the thermocouple is placed in the pilot flame. The resultant voltage, typically around 20 mV, operates the gas supply valve responsible for feeding the pilot. So long as the pilot flame remains lit, the thermocouple remains hot and holds the pilot gas valve open. If the pilot light goes out, the temperature will fall along with a corresponding drop in voltage across the thermocouple leads, removing power from the valve. The valve closes, shutting off the gas and halting this unsafe condition.

Some systems, known as millivolt control systems, extend this concept to the main gas valve as well. Not only does the voltage created by the pilot thermocouple activate the pilot gas valve, it is also routed through a thermostat to power the main gas valve as well. Here, a larger voltage is needed than in a pilot flame safety system described above, and a thermopile is used rather than a single thermocouple. Such a system requires no external source of electricity for its operation and so can operate during a power failure, provided all the related system components allow for this. Note that this excludes common forced air furnaces because external power is required to operate the blower motor, but this feature is especially useful for un-powered convection heaters.

A similar gas shut-off safety mechanism using a thermocouple is sometimes employed to ensure that the main burner ignites within a certain time period, shutting off the main burner gas supply valve should that not happen.

Out of concern for energy wasted by the standing pilot, designers of many newer appliances have switched to an electronically controlled pilot-less ignition, also called intermittent ignition. With no standing pilot flame, there is no risk of gas buildup should the flame go out, so these appliances do not need thermocouple-based safety pilot safety switches. As these designs lose the benefit of operation without a continuous source of electricity, standing pilots are still used in some appliances.

Thermopile radiation sensors

Thermopiles are used for measuring the intensity of incident radiation, typically visible or infrared light, which heats the hot junctions, while the cold junctions are on a heat sink. It is possible to measure radiative intensities of only a few μW/cm² with commercially available thermopile sensors. For example, some laser power meters are based on such sensors.

Manufacturing

Thermocouples can generally be used in the testing of prototype electrical and mechanical apparatus. For example, switchgear under test for its current carrying capacity may have thermocouples installed and monitored during a heat run test, to confirm that the temperature rise at rated current does not exceed designed limits.

External links : 

• NIST ITS-90 Thermocouple Database

• Thermocouple design guide

• Notes from a cold junction

• Mineral-Insulated Thermocouple Know-How

• Thermocouple Color Code Chart and Specifications

• Thermocouple Reference Information

Retrieved from “http://en.wikipedia.org/wiki/Thermocouple“

Categories: Heating, ventilating, and air conditioning | Thermometers | Sensors

]]> http://yonni1967.wordpress.com/2008/09/13/what-is-the-thermocouple/feed/ 1 yonni1967 gambar-tc1 http://yonni1967.wordpress.com/2008/09/13/method-of-servicing-electronic-equipment/ http://yonni1967.wordpress.com/2008/09/13/method-of-servicing-electronic-equipment/#comments Sat, 13 Sep 2008 14:37:15 +0000 yonni1967 http://yonni1967.wordpress.com/?p=87 ]]> Method of servicing electronic equipment.

The standard tool

By : Yonni Muhazir.

uwiga malang

In the first time if us on servicing electronic goods we think intricate network and make confusedly head. First step is bring damage goods to expert serviceman and buy his services. That is fair…..because improve of repairing electronic goods do not easy as which predicted most societies. Need an education and some practice have to many years to be able handle damage of electronic equipments. Experience of my self was a hard learn electronic skill from kiddy till now. To do that, I invite to all beginners which interest in the field of services electronic with me. I have finished my half age self-study and through by valuable experience. finally blessing by my school in result combination college and experience during many years I have succeeded of giving competent my family life blessing by that skilled.

Commonly…..Opening content of electronic box, initially it is true confuse have to, isn’t it? First question where we have to do start from this?. The visible is intricate of small cable and many path make confuse. Initially me, also that way too. Don’t be doleful, passing a little base lesson of electronics knowledge now will be reveal.

Early mind is feeling vexed, why this equipments can work ?. That just have enough ?. Both second step is human sense of base and enquire in itself : there is a way or systems taking care of this equipments so that like having soul. In this case I think back to nature that if ” something that take care of …” that out of sevice, so…. hence like a missing soul. Then…such as you think, hence the equipments will be “ die ”.

The “ Death ” of the electronics equipments caused by in-existence of electric current rationing to it. If human being have soul, hence the soul of electronics equipments is the electrics current – existence of it. Commonly trouble electrics current existence sometime indirectly “off” or lose but sometime there is can be chocked. This last situation so-called as “ sick ” cranky pain. This trouble happened caused by direct linking “short circuit” or “ intermitten ” connecting. Sometime also happened caused by component is out of age. Continuous and long-range exceed operation also can destroy this equipments. Also encumbering more exceed capacities causing over heating. The unstableness electricity from the stop contack also cause damage too. Most more because by follow consumer shares of carelessness conducted in this case.

Return to the ” soul ” was mentioned it, so… electrics current have stabilize passing without any disturbance!. Just a little trouble goes there, hence will happened like handicap performance at here!

Kinds of that trouble is :

• If that trouble at visual, looked into eye was bad picture, trouble example at TV equipment.

• If that trouble at voice, hence will be heard by hearting voice of our ear, follow the example at sound equipments.

• If that trouble at digital equipments kinds of numerator machine or computer, hence will be happened chaos arrangement of data and even will be “ hang “ !.

Then…. what method we must do in investigating above electrics current?. We have to assume that electrics current is the same precisely as water current character. Analogy electrics current measure is equal with flow of water where if current in a pipe stuff up hence happened stop current. Equipments to test and analyse electric current is :

• Avometre. This appliance good for analyzing an electronics existence of voltage, electrics current and resistance. This appliance have to always attend in a technician workbench and is standart technician equipments.

• Osciloscope. This equipments is a standard laboratory but do not always have to attend in beginner technician workbench.

In real factual of me, I am just  only requiring an Avometre, a tool set which compose from : some screwdriver, some kinds of forcepses, good quality soldering iron and that have last for search my earning life… ha..ha…ha…really..!!. and in experience day of my day I look for correct payment of me just rely on that simple equipments, but have succeeded all sort damage of electronics equipments. The secret is to treat electrics current as a real friend. Another secret again is to assuming electronics equipments as divided into some black box and in the handling of that was repair improve in per black box shares. This is important before you correct plunge into world business service of repairing electronic : ad for you have to honesty, at second, having to tough when remembering this world is struggle with a state :” something wrong and have to correct “. Don’t be to easy fulminate, and don’t be easy to stress..!!!!….

Best regards

Yonni 

in

Malang town

of

Indonesia

Mailto: yonni_1967@yahoo.co.id or yonni.muhazir@gmail.com

This is Invite to…..: All Malang town Hobbyiest electronics community ( Almahobel ). Hello..? Are you there ? Let us keep community forming such as have there be.. is….

Optoelectronics is the study and application of electronic devices that interact with light, and thus is usually considered a sub-field of photonics. In this context, light often includes invisible forms of radiation such as gamma rays, X-rays, ultraviolet and infrared. Optoelectronic devices are electrical-to-optical or optical-to-electrical transducers, or instruments that use such devices in their operation. Electro-optics is often erroneously used as a synonym, but is in fact a wider branch of physics that deals with all interactions between light and electric fields, whether or not they form part of an electronic device.

Optoelectronics is based on the quantum mechanical effects of light on semiconducting materials, sometimes in the presence of electric fields.

• Photoelectric or photovoltaic effect, used in:

  • photodiodes (including solar cells)

  • phototransistors

  • photomultipliers

  • integrated optical circuit (IOC) elements

• Photoconductivity, used in:

  • photoresistors

  • photoconductive camera tubes

  • charge-coupled imaging devices

• Stimulated emission, used in:

  • lasers

  • injection laser diodes

• Lossev effect, or radiative recombination, used in:

  • light-emitting diodes or LED

• Photoemissivity, used in

  • photoemissive camera tube

Important applications of optoelectronics include:

• Optocoupler

• optical fiber communications

Light

Light, or visible light, is electromagnetic radiation of a wavelength that is visible to the human eye (about 400–700 nm). In a scientific context, the word light is sometimes used to refer to the entire electromagnetic spectrum. Light is composed of an elementary particle called a photon.

Three primary properties of light are:

• Intensity, or brightness;

• Frequency or wavelength and;

• Polarization or direction of the wave oscillation.

Light can exhibit properties of both waves and particles. This property is referred to as wave-particle duality. The study of light, known as optics, is an important research area in modern physics.

Speed of light

The speed of light in a vacuum is exactly 299,792,458 m/s (about 186,282.397 miles per second). The speed of light depends upon the medium in which it is traveling, and the speed will be lower in a transparent medium. Although commonly called the “velocity of light”, technically the word velocity is a vector quantity, having both magnitude and direction. Speed refers only to the magnitude of the velocity vector. This fixed definition of the speed of light is a result of the modern attempt, in physics, to define the basic unit of length in terms of the speed of light, rather than defining the speed of light in terms of a length.

Different physicists have attempted to measure the speed of light throughout history. Galileo attempted to measure the speed of light in the seventeenth century. A good early experiment to measure the speed of light was conducted by Ole Rømer, a Danish physicist, in 1676. Using a telescope, Ole observed the motions of Jupiter and one of its moons, Io. Noting discrepancies in the apparent period of Io’s orbit, Rømer calculated that light takes about 18 minutes to traverse the diameter of Earth’s orbit. Unfortunately, this was not a value that was known at that time. If Ole had known the diameter of the earth’s orbit, he would have calculated a speed of 227,000,000 m/s.

Another, more accurate, measurement of the speed of light was performed in Europe by Hippolyte Fizeau in 1849. Fizeau directed a beam of light at a mirror several kilometers away. A rotating cog wheel was placed in the path of the light beam as it traveled from the source, to the mirror and then returned to its origin. Fizeau found that at a certain rate of rotation, the beam would pass through one gap in the wheel on the way out and the next gap on the way back. Knowing the distance to the mirror, the number of teeth on the wheel, and the rate of rotation, Fizeau was able to calculate the speed of light as 313,000,000 m/s.

Léon Foucault used an experiment which used rotating mirrors to obtain a value of 298,000,000 m/s in 1862. Albert A. Michelson conducted experiments on the speed of light from 1877 until his death in 1931. He refined Foucault’s methods in 1926 using improved rotating mirrors to measure the time it took light to make a round trip from Mt. Wilson to Mt. San Antonio in California. The precise measurements yielded a speed of 299,796,000 m/s.

Refraction

Light in a vacuum propagates at a maximum finite speed, defined above, and denoted by the symbol c. While passing through any other transparent medium, the speed of light slows to some fraction of c. The reduction of the speed of light traveling in a transparent medium is indicated by the refractive index, n, which is defined as:

where v denotes the speed that light travels in the transparent medium.

Note, n = 1 in a vacuum and n > 1 in a transparent medium.

When a beam of light crosses the boundary between a vacuum and another medium, or between two different mediums, the wavelength of the light changes, but the frequency remains constant. If the beam of light is not orthogonal to the boundary, the change in wavelength results in a change in the direction of the beam. This change of direction is known as refraction.

The refraction quality of lenses is frequently used to manipulate light in order to change the apparent size of images. Magnifying glasses, spectacles, contact lenses, microscopes and refracting telescopes are all examples of this manipulation.

Optics

The study of light and the interaction of light and matter is termed optics. The observation and study of optical phenomena such as rainbows and the aurora borealis offer many clues as to the nature of light as well as much enjoyment.

There are many sources of light. The most common light sources are thermal: a body at a given temperature emits a characteristic spectrum of black-body radiation. Examples include sunlight (the radiation emitted by the chromosphere of the Sun at around 6,000 K peaks in the visible region of the electromagnetic spectrum), incandescent light bulbs (which emit only around 10% of their energy as visible light and the remainder as infrared), and glowing solid particles in flames. The peak of the blackbody spectrum is in the infrared for relatively cool objects like human beings. As the temperature increases, the peak shifts to shorter wavelengths, producing first a red glow, then a white one, and finally a blue color as the peak moves out of the visible part of the spectrum and into the ultraviolet. These colors can be seen when metal is heated to “red hot” or “white hot”. The blue color is most commonly seen in a gas flame or a welder’s torch.

Atoms emit and absorb light at characteristic energies. This produces “emission lines” in the spectrum of each atom. Emission can be spontaneous, as in light-emitting diodes, gas discharge lamps (such as neon lamps and neon signs, mercury-vapor lamps, etc.), and flames (light from the hot gas itself—so, for example, sodium in a gas flame emits characteristic yellow light). Emission can also be stimulated, as in a laser or a microwave maser.

Acceleration of a free charged particle, such as an electron, can produce visible radiation: cyclotron radiation, synchrotron radiation, and bremsstrahlung radiation are all examples of this. Particles moving through a medium faster than the speed of light in that medium can produce visible Cherenkov radiation.

Certain chemicals produce visible radiation by chemoluminescence. In living things, this process is called bioluminescence. For example, fireflies produce light by this means, and boats moving through water can disturb plankton which produce a glowing wake.

Certain substances produce light when they are illuminated by more energetic radiation, a process known as fluorescence. This is used in fluorescent lights. Some substances emit light slowly after excitation by more energetic radiation. This is known as phosphorescence.

Phosphorescent materials can also be excited by bombarding them with subatomic particles. Cathodoluminescence is one example of this. This mechanism is used in cathode ray tube televisions.

Certain other mechanisms can produce light:

• scintillation

• electroluminescence

• sonoluminescence

• triboluminescence

• Cherenkov radiation

When the concept of light is intended to include very-high-energy photons (gamma rays), additional generation mechanisms include:

• radioactive decay

• particle–antiparticle annihilation

Optical theory

The Muslim scientist Ibn al-Haytham (c. 965-1040), known as Alhacen in the West, in his Book of Optics, developed a broad theory that explained vision, using geometry and anatomy, which stated that each point on an illuminated area or object radiates light rays in every direction, but that only one ray from each point, which strikes the eye perpendicularly, can be seen. The other rays strike at different angles and are not seen. He described the pinhole camera and invented the camera obscura, which produces an inverted image, and used it as an example to support his argument.This contradicted Ptolemy’s theory of vision that objects are seen by rays of light emanating from the eyes. Alhacen held light rays to be streams of minute particles that travelled at a finite speed. He improved Ptolemy’s theory of the refraction of light, and went on to discover the laws of refraction.

He also carried out the first experiments on the dispersion of light into its constituent colors. His major work Kitab al-Manazir was translated into Latin in the Middle Ages, as well his book dealing with the colors of sunset. He dealt at length with the theory of various physical phenomena like shadows, eclipses, the rainbow. He also attempted to explain binocular vision, and gave a correct explanation of the apparent increase in size of the sun and the moon when near the horizon. Because of his extensive research on optics, Al-Haytham is considered the father of modern optics.

Al-Haytham also correctly argued that we see objects because the sun’s rays of light, which he believed to be streams of tiny particles travelling in straight lines, are reflected from objects into our eyes. He understood that light must travel at a large but finite velocity, and that refraction is caused by the velocity being different in different substances. He also studied spherical and parabolic mirrors, and understood how refraction by a lens will allow images to be focused and magnification to take place. He understood mathematically why a spherical mirror produces aberration.

Wave theory

In the 1660s, Robert Hooke published a wave theory of light. Christiaan Huygens worked out his own wave theory of light in 1678, and published it in his Treatise on light in 1690. He proposed that light was emitted in all directions as a series of waves in a medium called the Luminiferous ether. As waves are not affected by gravity, it was assumed that they slowed down upon entering a denser medium.

Thomas Young’s sketch of the two-slit experiment showing the diffraction of light. Young’s experiments supported the theory that light consists of waves.

The wave theory predicted that light waves could interfere with each other like sound waves (as noted around 1800 by Thomas Young), and that light could be polarized. Young showed by means of a diffraction experiment that light behaved as waves. He also proposed that different colors were caused by different wavelengths of light, and explained color vision in terms of three-colored receptors in the eye.

Another supporter of the wave theory was Leonhard Euler. He argued in Nova theoria lucis et colorum (1746) that diffraction could more easily be explained by a wave theory.

Later, Augustin-Jean Fresnel independently worked out his own wave theory of light, and presented it to the Académie des Sciences in 1817. Simeon Denis Poisson added to Fresnel’s mathematical work to produce a convincing argument in favour of the wave theory, helping to overturn Newton’s corpuscular theory.

The weakness of the wave theory was that light waves, like sound waves, would need a medium for transmission. A hypothetical substance called the luminiferous aether was proposed, but its existence was cast into strong doubt in the late nineteenth century by the Michelson-Morley experiment.

Newton’s corpuscular theory implied that light would travel faster in a denser medium, while the wave theory of Huygens and others implied the opposite. At that time, the speed of light could not be measured accurately enough to decide which theory was correct. The first to make a sufficiently accurate measurement was Léon Foucault, in 1850. His result supported the wave theory, and the classical particle theory was finally abandoned.

Electromagnetic theory

A linearly-polarized light wave frozen in time and showing the two oscillating components of light; an electric field and a magnetic field perpendicular to each other and to the direction of motion (a transverse wave).

In 1845, Michael Faraday discovered that the angle of polarization of a beam of light as it passed through a polarizing material could be altered by a magnetic field, an effect now known as Faraday rotation. This was the first evidence that light was related to electromagnetism. Faraday proposed in 1847 that light was a high-frequency electromagnetic vibration, which could propagate even in the absence of a medium such as the ether.

Faraday’s work inspired James Clerk Maxwell to study electromagnetic radiation and light. Maxwell discovered that self-propagating electromagnetic waves would travel through space at a constant speed, which happened to be equal to the previously measured speed of light. From this, Maxwell concluded that light was a form of electromagnetic radiation: he first stated this result in 1862 in On Physical Lines of Force. In 1873, he published A Treatise on Electricity and Magnetism, which contained a full mathematical description of the behaviour of electric and magnetic fields, still known as Maxwell’s equations. Soon after, Heinrich Hertz confirmed Maxwell’s theory experimentally by generating and detecting radio waves in the laboratory, and demonstrating that these waves behaved exactly like visible light, exhibiting properties such as reflection, refraction, diffraction, and interference. Maxwell’s theory and Hertz’s experiments led directly to the development of modern radio, radar, television, electromagnetic imaging, and wireless communications.

Light-emitting diode

LED Image

A light-emitting diode (LED) is a semiconductor diode that emits incoherent narrow-spectrum light when electrically biased in the forward direction of the p-n junction, as in the common LED circuit. This effect is a form of electroluminescence.

An LED is usually a small area source, often with extra optics added to the chip that shapes its radiation pattern. LED’s are often used as small indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be infrared, visible, or near-ultraviolet. An LED can be used as a regular household light source.

LED technology

Like a normal diode, an LED consists of a chip of semiconducting material impregnated, or doped, with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon.

The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect band gap materials. The materials used for an LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light.

LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors.

LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate. Substrates that are transparent to the emitted wavelength, and backed by a reflective layer, increase the LED efficiency. The refractive index of the package material should match the index of the semiconductor, otherwise the produced light gets partially reflected back into the semiconductor, where it may be absorbed and turned into additional heat, thus lowering the efficiency. This type of reflection also occurs at the surface of the package if the LED is coupled to a medium with a different refractive index such as a glass fiber or air. The refractive index of most LED semiconductors is quite high, so in almost all cases the LED is coupled into a much lower-index medium. The large index difference makes the reflection quite substantial (per the Fresnel coefficients), and this is usually one of the dominant causes of LED inefficiency. Often more than half of the emitted light is reflected back at the LED-package and package-air interfaces. The reflection is most commonly reduced by using a dome-shaped (half-sphere) package with the diode in the center so that the outgoing light rays strike the surface perpendicularly, at which angle the reflection is minimized. An anti-reflection coating may be added as well. The package may be cheap plastic, which may be colored, but this is only for cosmetic reasons or to improve the contrast ratio; the color of the packaging does not substantially affect the color of the light emitted. Other strategies for reducing the impact of the interface reflections include designing the LED to reabsorb and reemit the reflected light (called photon recycling) and manipulating the microscopic structure of the surface to reduce the reflectance, either by introducing random roughness or by creating programmed moth eye surface patterns.

Conventional LEDs are made from a variety of inorganic semiconductor materials, producing the following colors:

• Aluminium gallium arsenide (AlGaAs) — red and infrared

• Aluminium gallium phosphide (AlGaP) — green

• Aluminium gallium indium phosphide (AlGaInP) — high-brightness orange-red, orange, yellow, and green

• Gallium arsenide phosphide (GaAsP) — red, orange-red, orange, and yellow

• Gallium phosphide (GaP) — red, yellow and green

• Gallium nitride (GaN) — green, pure green (or emerald green), and blue also white (if it has an AlGaN Quantum Barrier)

• Indium gallium nitride (InGaN) — 450nm – 470nm — near ultraviolet, bluish-green and blue

• Silicon carbide (SiC) as substrate — blue

• Silicon (Si) as substrate — blue (under development)

• Sapphire (Al₂O₃) as substrate — blue

• Zinc selenide (ZnSe) — blue

• Diamond (C) — ultraviolet

• Aluminium nitride (AlN), aluminium gallium nitride (AlGaN), aluminium gallium indium nitride (AlGaInN) — near to far ultraviolet (down to 210 nm)

With this wide variety of colors, arrays of multicolor LEDs can be designed to produce unconventional color patterns.

Ultraviolet and blue LEDs

Ultraviolet GaN LEDs.

Blue LEDs are based on the wide band gap semiconductors GaN (gallium nitride) and InGaN (indium gallium nitride). They can be added to existing red and green LEDs to produce the impression of white light, though white LEDs today rarely use this principle.

The first blue LEDs were made in 1971 by Jacques Pankove (inventor of the gallium nitride LED) at RCA Laboratories. However, these devices were too feeble to be of much practical use. In the late 1980s, key breakthroughs in GaN epitaxial growth and p-type doping by Akasaki and Amano (Nagoya, Japan) ushered in the modern era of GaN-based optoelectronic devices. Building upon this foundation, in 1993 high brightness blue LEDs were demonstrated through the work of Shuji Nakamura at Nichia Corporation.

By the late 1990s, blue LEDs had become widely available. They have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers. By varying the relative InN-GaN fraction in the InGaN quantum wells, the light emission can be varied from violet to amber. AlGaN aluminium gallium nitride of varying AlN fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of the InGaN-GaN blue/green devices. If the active quantum well layers are GaN, as opposed to alloyed InGaN or AlGaN, the device will emit near-ultraviolet light with wavelengths around 350–370 nm. Green LEDs manufactured from the InGaN-GaN system are far more efficient and brighter than green LEDs produced with non-nitride material systems.

With aluminium containing nitrides, most often AlGaN and AlGaInN, even shorter wavelengths are achievable. Ultraviolet LEDs are becoming available on the market, in a range of wavelengths. Near-UV emitters at wavelengths around 375–395 nm are already cheap, common to encounter e.g., as black light lamp replacements for inspection of anti-counterfeiting UV watermarks in some documents and paper currencies. Shorter wavelength diodes, while substantially more expensive, are commercially available for wavelengths down to 247 nm. As the photosensitivity of microorganisms approximately matches the absorption spectrum of DNA, with peak at about 260 nm, UV LEDs emitting at 250–270 nm are prospective for disinfecting devices.

Wavelengths down to 210 nm were obtained in laboratories using aluminium nitride.

While not actually an LED as such, an ordinary NPN bipolar transistor will emit violet light if its emitter-base junction is subjected to non-destructive reverse breakdown. This is easy to demonstrate by filing the top off a metal-can transistor (BC107, 2N2222 or similar) and biasing it well above emitter-base breakdown (≥ 20 V) via a current limiting resistor.

White LEDs

A combination of red, green and blue LEDs can produce the impression of white light, though white LEDs today rarely use this principle. Most “white” LEDs in production today are modified blue LEDs: GaN-based, InGaN-active-layer LEDs emit blue light of wavelengths between 450 nm and 470 nm. This InGaN-GaN structure is covered with a yellowish phosphor coating usually made of cerium-doped yttrium aluminum garnet (Ce³⁺:YAG) crystals which have been powdered and bound in a type of viscous adhesive. The LED chip emits blue light, part of which is efficiently converted to a broad spectrum centered at about 580 nm (yellow) by the Ce³⁺:YAG. Since yellow light stimulates the red and green receptors of the eye, the resulting mix of blue and yellow light gives the appearance of white, the resulting shade often called “lunar white”. This approach was developed by Nichia and has been used since 1996 for the manufacture of white LEDs.

The pale yellow emission of the Ce³⁺:YAG can be tuned by substituting the cerium with other rare earth elements such as terbium and gadolinium and can even be further adjusted by substituting some or all of the aluminum in the YAG with gallium. Due to the spectral characteristics of the diode, the red and green colors of objects in its blue yellow light are not as vivid as in broad-spectrum light. Manufacturing variations and varying thicknesses in the phosphor make the LEDs produce light with different color temperatures, from warm yellowish to cold bluish; the LEDs have to be sorted during manufacture by their actual characteristics. Philips Lumileds patented conformal coating process addresses the issue of varying phosphor thickness, giving the white LEDs a more consistent spectrum of white light.

Spectrum of a “white” LED clearly showing blue light which is directly emitted by the GaN-based LED (peak at about 465 nanometers) and the more broadband stokes shifted light emitted by the Ce³⁺:YAG phosphor which extends from around 500 to 700 nanometers.

White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium-based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu, Al). This is a method analogous to the way fluorescent lamps work. However the ultraviolet light causes photodegradation to the epoxy resin and many other materials used in LED packaging, causing manufacturing challenges and shorter lifetimes. This method is less efficient than the blue LED with YAG:Ce phosphor, as the Stokes shift is larger and more energy is therefore converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both approaches offer comparable brightness.

The newest method used to produce white light LEDs uses no phosphors at all and is based on homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate which simultaneously emits blue light from its active region and yellow light from the substrate.

A new technique developed by Michael Bowers, a graduate student at Vanderbilt University in Nashville, involves coating a blue LED with quantum dots that glow white in response to the blue light from the LED. This technique produces a warm, yellowish-white light similar to that produced by incandescent bulbs.

Organic light-emitting diodes (OLEDs)

Combined spectral curves for blue, yellow-green, and high brightness red solid-state semiconductor LEDs. FWHM spectral bandwidth is approximately 24–27 nanometres for all three colors.

If the emitting layer material of an LED is an organic compound, it is known as an Organic Light Emitting Diode (OLED). To function as a semiconductor, the organic emitting material must have conjugated pi bonds. The emitting material can be a small organic molecule in a crystalline phase, or a polymer. Polymer materials can be flexible; such LEDs are known as PLEDs or FLEDs.

Compared with regular LEDs, OLEDs are lighter, and polymer LEDs can have the added benefit of being flexible. Some possible future applications of OLEDs could be:

• Inexpensive, flexible displays

• Light sources

• Wall decorations

• Luminous cloth

OLEDs have been used to produce visual displays for portable electronic devices such as cellphones, digital cameras, and MP3 players. Larger displays have been demonstrated, but their life expectancy is still far too short (<1,000 hours) to be practical.

Operational parameters and efficiency

Most typical LEDs are designed to operate with no more than 30–60 milliwatts of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one watt. These LEDs used much larger semiconductor die sizes to handle the large power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat removal from the LED die.

One of the key advantages of LED-based lighting is its high efficiency, as measured by its light output per unit power input. White LEDs quickly matched and overtook the efficiency of standard incandescent lighting systems. In 2002, Lumileds made five-watt LEDs available with a luminous efficacy of 18–22 lumens per watt. For comparison, a conventional 60–100 watt incandescent lightbulb produces around 15 lumens/watt, and standard fluorescent lights produce up to 100 lumens/watt. (The luminous efficacy article discusses these comparisons in more detail.)

In September 2003, a new type of blue LED was demonstrated by the company Cree, Inc. to provide 24 mW at 20 mA. This produced a commercially packaged white light giving 65 lumens per watt at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006 they demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. Also, Seoul Semiconductor has plans for 135 lm/W by 2007 and 145 lm/W by 2008, which would be approaching an order of magnitude improvement over standard incandescents and better even than standard fluorescents. Nichia Corp. has developed a white light LED with luminous efficacy of 150 lm/W at a forward current of 20 mA.

It should be noted that high-power (≥ 1 Watt) LEDs are necessary for practical general lighting applications. Typical operating currents for these devices begin at 350 mA. The highest efficiency high-power white LED is claimed by Philips Lumileds Lighting Co. with a luminous efficacy of 115 lm/W (350 mA).

Today, OLEDs operate at substantially lower efficiency than inorganic (crystalline) LEDs. The best luminous efficacy of an OLED so far is about 10% of the theoretical maximum of 683, or about 68 lm/W. These claim to be much cheaper to fabricate than inorganic LEDs, and large arrays of them can be deposited on a screen using simple printing methods to create a color graphical display.

Considerations in use

Unlike incandescent light bulbs, which light up regardless of the electrical polarity, LEDs will only light with correct electrical polarity. When the voltage across the p-n junction is in the correct direction, a significant current flows and the device is said to be forward-biased. If the voltage is of the wrong polarity, the device is said to be reverse biased, very little current flows, and no light is emitted. Some LEDs can be operated on an alternating current voltage, but they will only light with positive voltage, causing the LED to turn on and off at the frequency of the AC supply.

While the only 100% accurate way to determine the polarity of an LED is to examine its datasheet, these methods are usually reliable:

Less reliable methods of determining polarity are:

While it is not an officially reliable method, it is almost universally true that the cup that holds the LED die corresponds to the cathode. It is strongly recommended to apply a safe voltage and observe the illumination as a test regardless of what method is used to determine the polarity.

Because the voltage versus current characteristics of an LED are much like any diode (that is, current approximately an exponential function of voltage), a small voltage change results in a huge change in current. Added to deviations in the process this means that a voltage source may barely make one LED light while taking another of the same type beyond its maximum ratings and potentially destroying it.

Since the voltage is logarithmically related to the current it can be considered to remain largely constant over the LEDs operating range. Thus the power can be considered to be almost proportional to the current. In order to keep power nearly constant with variations in supply and LED characteristics, the power supply should be a “current source”, that is, it should supply an almost constant current. If high efficiency is not required (e.g., in most indicator applications), an approximation to a current source made by connecting the LED in series with a current limiting resistor to a constant voltage source is generally used.

Most LEDs have low reverse breakdown voltage ratings, so they will also be damaged by an applied reverse voltage of more than a few volts. Since some manufacturers don’t follow the indicator standards above, if possible the data sheet should be consulted before hooking up an LED, or the LED may be tested in series with a resistor on a sufficiently low voltage supply to avoid the reverse breakdown. If it is desired to drive an LED directly from an AC supply of more than the reverse breakdown voltage then it may be protected by placing a diode (or another LED) in inverse parallel.

LEDs can be purchased with built in series resistors. These can save PCB space and are especially useful when building prototypes or populating a PCB in a way other than its designers intended. However the resistor value is set at the time of manufacture, removing one of the key methods of setting the LED’s intensity. To increase efficiency (or to allow intensity control without the complexity of a DAC), the power may be applied periodically or intermittently; so long as the flicker rate is greater than the human flicker fusion threshold, the LED will appear to be continuously lit.

Provided there is sufficient voltage available, multiple LEDs can be connected in series with a single current limiting resistor. Parallel operation is generally problematic. The LEDs have to be of the same type in order to have a similar forward voltage. Even then, variations in the manufacturing process can make the odds of satisfactory operation low.

Bicolor LED units contain two diodes, one in each direction (that is, two diodes in inverse parallel) and each a different color (typically red and green), allowing two-color operation or a range of apparent colors to be created by altering the percentage of time the voltage is in each polarity. Other LED units contain two or more diodes (of different colors) arranged in either a common anode or common cathode configuration. These can be driven to different colors without reversing the polarity, however, more than two electrodes (leads) are required.

LEDs are usually constantly illuminated when a current passes through them, but flashing LEDs are also available. Flashing LEDs resemble standard LEDs but they contain an integrated multivibrator circuit inside which causes the LED to flash with a typical period of one second. This type of LED comes most commonly as red, yellow, or green. Most flashing LEDs emit light of a single wavelength, but multicolored flashing LEDs are available too.

Generally, for newer common standard LEDs in 3 mm or 5 mm packages, the following forward DC potential differences are typically measured. The forward potential difference depending on the LED’s chemistry, temperature, and on the current (values here are for approx. 20 milliamperes, a commonly found maximum value).

Many LEDs are rated at 5 V maximum reverse voltage.

LEDs also behave as photocells, and will generate a current depending on the ambient light. They are not efficient as photocells, and will only produce a few microamps, but will put out a surprising voltage level, as much as 2 or 3 volts. This is enough to operate an amplifier or CMOS logic gate. This effect can be used to make an inexpensive light sensor, for example to decide when to turn on an LED illuminator.

Advantages of using LEDs

• LEDs produce more light per watt than do incandescent bulbs; this is useful in battery powered or energy-saving devices.

• LEDs can emit light of an intended color without the use of color filters that traditional lighting methods require. This is more efficient and can lower initial costs.

• The solid package of an LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner.

• When used in applications where dimming is required, LEDs do not change their color tint as the current passing through them is lowered, unlike incandescent lamps, which turn yellow.

• LEDs are ideal for use in applications that are subject to frequent on-off cycling, unlike fluorescent lamps that burn out more quickly when cycled frequently, or HID lamps that require a long time before restarting.

• LEDs, being solid state components, are difficult to damage with external shock. Fluorescent and incandescent bulbs are easily broken if dropped on the ground.

• LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. Fluorescent tubes typically are rated at about 30,000 hours, and incandescent light bulbs at 1,000–2,000 hours.^{[citation needed]}

• LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent bulbs.

• LEDs light up very quickly. A typical red indicator LED will achieve full brightness in microseconds; LEDs used in communications devices can have even faster response times.

• LEDs can be very small and are easily populated onto printed circuit boards.

• LEDs do not contain mercury, while compact fluorescent lamps do.

LEDs are produced in an array of shapes and sizes. The 5 mm cylindrical package (red, fifth from the left) is the most common, estimated at 80% of world production. The color of the plastic lens is often the same as the actual color of light emitted, but not always. For instance, purple plastic is often used for infrared LEDs, and most blue devices have clear housings. There are also LEDs in extremely tiny packages, such as those found on blinkies (not shown).

Disadvantages of using LEDs

• LEDs are currently more expensive, price per lumen, on an initial capital cost basis, than more conventional lighting technologies. The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed. However, when considering the total cost of ownership (including energy and maintenance costs), LEDs far surpass incandescent or halogen sources and begin to threaten compact fluorescent lamps. In December 2007, scientist at Glasgow University claimed to have found a way to make Light Emitting Diodes brighter and use less power than energy efficient light bulbs currently on the market by imprinting the holes into billions of LEDs in a new and cost effective method using a process known as nanoimprint lithography.

• LED performance largely depends on the ambient temperature of the operating environment. Driving an LED hard in high ambient temperatures may result in overheating of the LED package, eventually leading to device failure. Adequate heat-sinking is required to maintain long life. This is especially important when considering automotive, medical, and military applications where the device must operate over a large range of temperatures, and is required to have a low failure rate.

• LEDs must be supplied with the correct current. This can involve shunt resistors or regulated power supplies.

• The spectrum of some white LEDs differs significantly from a black body radiator, such as the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under LED illumination than sunlight or incandescent sources, due to metamerism. However, it should be noted that color rendering properties of common fluorescent lamps are often inferior to what is now available in state-of-art white LEDs.

• LEDs do not approximate a “point source” of light, so cannot be used in applications that need a sharply directive and collimated beam. LEDs are not capable of providing directivity below a few degrees. In such cases LASERs (or amplified spontaneous emission devices) may be a better option.

• There is increasing concern that blue LEDs and white LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1-05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems.

Types

There are 3 main types of LEDs: miniature LEDs, alphanumeric LEDs, and lighting LEDs.

Miniature LEDs

These are mostly single die LEDs used as indicators, and come in various size packages:

• surface mount

• 2mm

• 3mm

• 5mm

• Other sizes are also available, but less common.

There are 3 main categories of miniature single die LEDs:

• Low current – typically rated for 2mA at around 2v (apx 4mW consumption).

• Standard - 20mA LEDs at around 2v (apx 40mW) for red, orange, yellow & green, and 20mA at 4-5v (apx 0.1W) for blue, violet and white.

• Ultra high output – 20mA at apx 2v or 4-5v, designed for viewing in direct sunlight. These have enough light output to light a very small object, or may be used in low output torches.

Multicolour LEDs

Bicolour LEDs contain 2 dice of different colours connected back to back, and can produce any of 3 colours. Current flow in one direction produces one colour, current in the other direction produces the other colour, and bidirectional current produces both colours mixed together.

Tricolour LEDs contain 3 dice. Often these are RGB dice, but not always. These LEDs can be driven to produce a wider range of colours, and in the case of RBG LEDS nearly the whole visible spectrum of colours.

5v & 12v LEDs

These are miniature LEDs incorporating a series resistor, and may be connected directly to 5v or 12v.

Flashing LEDs

These miniature LEDs flash when connected to 5v or 12v. Used as attention seeking indicators where it is desired to avoid the complexity of external electronics.

Alphanumeric LEDs

LED displays are available in 7 segment and starburst format. 7 segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters.

7 segment LED displays were in widespread use in the 1970s and 1980s, but increasing use of LCD displays, with their lower power consumption and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.

Lighting LEDs

LED lamps (also called LED bars or Illuminators) are usually clusters of LEDs in a suitable housing. They come in different shapes, among them the light bulb shape with a large E27 Edison screw and MR16 shape with a bi-pin base. Other models might have a small Edison E14 fitting, GU5.3 (Bipin cap) or GU10 (bayonet socket). This includes low voltage (typically 12 V halogen-like) varieties and replacements for regular AC mains (120-240 V AC) lighting. Currently the latter are less widely available but this is changing rapidly.

LED applications

1. LED panel light source used in an experiment on plant growth. The findings of such experiments may be used to grow food in space on long duration missions.

2. Light sources for machine vision systems.

3. An LED destination display on a bus. Note how the camera has had difficulty catching all the LEDs.

4. Old calculator LED display.

5. Flashlights and lanterns that utilise white LEDs are becoming increasingly popular due to their durability and longer battery life.

6. Single high-brightness LED with a glass lens creates a bright carrier beam that can stream DVD-quality video over considerable distances. The device, RONJA, can be built very simply by enthusiasts.

7. LED lights on an Audi S6

List of LED applications

Some of these applications are further elaborated upon in the following text.

• Streetlights

• Large scale video displays

• Architectural lighting

• Status indicators on all sorts of equipment

• Traffic lights and signals

• Light source for machine vision systems, requiring bright, focused, homogeneous and possibly strobed illumination.

• Exit signs

• Motorcycle and Bicycle lights

• Toys and recreational sporting goods, such as the Flashflight

• Railroad crossing signals

• Continuity indicators

• Flashlights, including some mechanically powered models.

• Emergency vehicle lighting

• Elevator Push Button Lighting

• Thin, lightweight message displays at airports and railway stations and as destination displays for trains, buses, trams and ferries.

• Red or yellow LEDs are used in indicator and alphanumeric displays in environments where night vision must be retained: aircraft cockpits, submarine and ship bridges, astronomy observatories, and in the field, e.g. night time animal watching and military field use.

• Red, yellow, green, and blue LEDs can be used for model railroading applications

• Remote controls, such as for TVs and VCRs, often use infrared LEDs.

• The Nintendo Wii’s sensor bar uses infrared LEDs.

• In optical fiber and Free Space Optics communications.

• In dot matrix arrangements for displaying messages.

• Glowlights, as a more expensive but longer lasting and reusable alternative to Glowsticks.

• Grow lights composed of LEDs are more efficient, both because LEDs produce more lumens per watt than other alternatives, and also because they can be tuned to the specific wavelengths plants can make the most use of.^{[citation needed]}

• Movement sensors, for example in optical computer mice

• Because of their long life and fast switching times, LEDs have been used for automotive high-mounted brake lights and truck and bus brake lights and turn signals for some time, but many high-end vehicles are now starting to use LEDs for their entire rear light clusters. Besides the gain in reliability, this has styling advantages because LEDs are capable of forming much thinner lights than incandescent lamps with parabolic reflectors. The significant improvement in the time taken to light up (perhaps 0.5s faster than an incandescent bulb) improves safety by giving drivers more time to react. It has been reported that at normal highway speeds this equals one car length increased reaction time for the car behind. White LED headlamps are beginning to make an appearance.

• Backlighting for LCD televisions and displays. The availability of LEDs in specific colors (RGB) enables a full-spectrum light source which expands the color gamut by as much as 45%.

• New stage lighting equipment is being developed with LED sources in primary red-green-blue arrangements.

• Lumalive, a photonic textile

• LED-based Christmas lights have been available since 2002, but are only now beginning to gain in popularity and acceptance due to their higher initial purchase cost when compared to similar incandescent-based Christmas lights. For example, as of 2006, a set of 50 incandescent lights might cost US$2, while a similar set of 50 LED lights might cost US$10. The purchase cost can be even higher for single-color sets of LED lights with rare or recently-introduced colors, such as purple, pink or white. Regardless of the higher initial purchase price, the total cost of ownership for LED Christmas lights would eventually be lower than the TCO for similar incandescent Christmas lights^{[citation needed]} since an LED requires much less power to output the same amount of light as a similar incandescent bulb. More to the point, LEDs have practically unlimited life and are hard-wired rather than using unreliable sockets as do replaceable bulbs. So a set of LED lights can be expected to outlive many incandescent sets, and without any maintenance.

• LED phototherapy for acne using blue or red LEDs has been proven to significantly reduce acne over a 3 month period.^{[citation needed]}

• As a medium quality voltage reference in electronic circuits. The forward voltage drop (e.g., about 1.7 V for a normal red LED) can be used instead of a Zener diode in low-voltage regulators. Although LED forward voltage is much more current-dependent than a good Zener, Zener diodes are not available below voltages of about 3 V.

• Some flatbed scanners use an array of red, green, and blue LEDs rather than the typical cold-cathode fluorescent lamp as the light source. Having independent control of three illuminant colors allows the scanner to calibrate itself for more accurate color balance, and there is no need for warm-up.

• Computers, for hard drive activity and power on. Some custom computers feature LED accent lighting to draw attention to a given component. Many computer manufactuers use LEDs to tell the user its current state. One example would be the Mac, which tells its user when it is asleep by fading the LED activity lights in and out, in and out.

• Light bulbs

• Lanterns

Optoisolators and optocouplers

Optocoupler schematic showing LED and phototransistorAn LED may be combined with a photodiode or phototransistor in a single electronic device to provide a signal path with electrical isolation between two circuits. An optoisolator will have typical breakdown voltages between the input and output circuits of typically 500 to 3000 volts. This is especially useful in medical equipment where the signals from a low voltage sensor circuit (usually battery powered) in contact with a living organism must be electrically isolated from any possible electrical failure in a recording or montoring device operating at potentially dangerous voltages. An optoisolator also allows information to be transferred between circuits not sharing a common ground potential. An optocoupler may not have such high breakdown voltages and may even share a ground between input and output, but both types are useful in preventing electrical noise, particularly common mode electrical noise, on a sensor circuit from being transferred to the receiving circuit (where it may adversly affect the operation or durability of various components) and/or transferring a noisy signal. Optoisolators are also used in the feedback circuit of a DC to DC converter, allowing power to be transferred while retaining electrical isolation between the input and output.

Indicator LEDs

Miniature indicator LEDs are normally driven from low voltage DC via a current limiting resistor. Currents of 2mA, 10mA and 20mA are common. Some low current indicators are only rated to 2mA, and should not be driven at higher current.

Sub-mA indicators may be made by driving ultrabright LEDs at very low current. Efficacy tends to reduce at low currents, but indicators running on 100uA are still practical. The cost of ultrabrights is higher than 2mA indicator LEDs.

LEDs have a low max repeat reverse voltage rating, ranging from apx 2v to 5v, and this can be a problem in some apps. Back to back LEDs are immune to this problem. These are available in single colour as well as bicolor types. There are various strategies for reverse voltage handling.

In niche applications such as IR therapy, LEDs are often driven at far above rated current. This causes high failure rate and occasional LED explosions. Thus many parallel strings are used, and a safety screen and ongoing maintenance are required.

Alphanumeric LEDs

These use the same drive strategy as indicator LEDs, the only difference being the larger number of channels, each with its own resistor. 7 segment and starburst LED arrays are available in both common anode or common cathode forms.

Lighting LEDs on mains

A CR dropper followed by full wave rectification is the usual ballast with series-parallel LED clusters.

A single series string minimises dropper losses, while parallelled strings increase reliability. In practice usually 3 strings or more are used.

Operation on square wave and modified sine wave (MSW) sources, such as many invertors, causes heavily increased resistor dissipation in CR droppers, and LED ballasts designed for sine wave use tend to burn on non-sine waveforms. The non-sine waveform also causes high peak LED currents, heavily shortening LED life. An inductor & rectifier makes a more suitable ballast for such use, and other options are also possible.

Lighting LEDs on low voltage

LEDs are normally operated in parallel strings of series LEDs, with the total LED voltage typically adding up to around 2/3 of the supply voltage, and resistor current control for each string.

LED current is proportional to power supply (PSU) voltage minus total LED string voltage. Where battery sources are used, the PSU voltage can vary widely, causing large changes in LED current and light output. For such applications, a constant current regulator is preferred to resistor control. Low drop-out (LDO) constant current regs also allow the total LED string voltage to be a higher percentage of PSU voltage, resulting in improved efficiency and reduced power use.

Torches run 1 or more lighting LEDs on a low voltage battery. These usually use a resistor ballast.

In disposable coin cell powered keyring type LED lights, the resistance of the cell itself is usually the only current limiting device. The cell should not therefore be replaced with a lower resistance type, such as one using a different battery chemistry.

Finally, an LED can be run from a single cell by use of a constant current switched mode invertor. The extra expense makes this option unpopular.

LED panels

The 1,500 foot long LED display on the Fremont Street Experience is currently the largest in the world.

There are two types of LED panels: conventional, using discrete LEDs, and surface mounted device (SMD) panels. Most outdoor screens and some indoor screens are built around discrete LEDs, also known as individually mounted LEDs. A cluster of red, green, and blue diodes is driven together to form a full-color pixel, usually square in shape. These pixels are spaced evenly apart and are measured from center to center for absolute pixel resolution. The largest LED display in the world is over 1,500 foot (457.2 m) long and is located in Las Vegas, Nevada covering the Fremont Street Experience.

Most indoor screens on the market are built using SMD technology—a trend that is now extending to the outdoor market. An SMD pixel consists of red, green, and blue diodes mounted on a chipset, which is then mounted on the driver PC board. The individual diodes are smaller than a pinhead and are set very close together. The difference is that the maximum viewing distance is reduced by 25% from the discrete diode screen with the same resolution.

LED panels allow for smaller sets of interchangeable LEDs to be one large display.

Indoor use generally requires a screen that is based on SMD technology and has a minimum brightness of 600 candelas per square meter (unofficially called nits). This will usually be more than sufficient for corporate and retail applications, but under high ambient-brightness conditions, higher brightness may be required for visibility. Fashion and auto shows are two examples of high-brightness stage lighting that may require higher LED brightness. Conversely, when a screen may appear in a shot on a television show, the requirement will often be for lower brightness levels with lower color temperatures (common displays have a white point of 6500 to 9000 K, which is much bluer than the common lighting on a television production set).

A large LED screen in Razorback Stadium

For outdoor use, at least 2,000 nits are required for most situations, whereas higher brightness types of up to 5,000 nits cope even better with direct sunlight on the screen. (The brightness of LED panels can be reduced from the designed maximum, if required.)

Suitable locations for large display panels are identified by factors such as line of sight, local authority planning requirements (if the installation is to become semi-permanent), vehicular access (trucks carrying the screen, truck-mounted screens, or cranes), cable runs for power and video (accounting for both distance and health and safety requirements), power, suitability of the ground for the location of the screen (if there are no pipes, shallow drains, caves, or tunnels that may not be able to support heavy loads), and overhead obstructions.

Early LED flat panel TV history

The first recorded flat panel LED television screen prototype to be developed was by James P. Mitchell in 1977. The modular, scalable display was enabled by MV50 LEDs and newly available TTL (transistor transistor logic) memory addressing circuit technology. The prototype and paper were displayed at an Engineering Exposition in Anaheim May 1978, and organized by the Science Service in Washington D.C. The LED TV display received special recognition from NASA, General Motors Corporation and area universities including The University of California Irvine, Robert M. Saunders Prof. of Engineering and IEEE President 1977. Additionally, technology business representatives from the U.S. and overseas witnessed operation of the monochromatic LED television display. The prototype remains operational. An LCD (liquid crystal display) matrix design was also presented in the accompanying scientific paper as a future television display method using a similar array scanning design.

The early display prototype was red monochromatic. Low-cost efficient blue LEDs did not emerge until the early 1990s, completing the desired RGB color triad. High-brightness colors gradually emerged in the 1990s enabling new designs for outdoor signage and huge video displays for billboards and stadiums.

Multi-touch sensing

Since LEDs share some basic physical properties with photodiodes, which also use p-n junctions with band gap energies in the visible light wavelengths, they can also be used for photo detection. These properties have been known for some time, but more recently so-called bidirectional LED matrices have been proposed as a method of touch-sensing. In 2003, Dietz, Yerazunis, and Leigh published a paper describing the use of LEDs as cheap sensor devices.

In this usage, various LEDs in the matrix are quickly switched on and off. LEDs that are on shine light onto a user’s fingers or a stylus. LEDs that are off function as photodiodes to detect reflected light from the fingers or stylus. The voltage thus induced in the reverse-biased LEDs can then be read by a microprocessor, which interprets the voltage peaks and then also uses them elsewhere.

Laser

Experiment with a LASER(Light amplified by stimulated emmision of radiation) (US Military)

A laser is an electronic-optical device that produces coherent radiation. The term “laser” is an acronym for Light Amplified by Stimulated Emission of Radiation. A typical laser emits light in a narrow, low-divergence beam and with a well-defined wavelength (i.e., monochromatic, corresponding to a particular colour if the laser is operating in the visible spectrum). This is in contrast to a light source such as the incandescent light bulb, which emits into a large solid angle and over a wide spectrum of wavelength.