Anopto-isolatorcontains a source (emitter) of light, almost always a near infrared light-emitting diode (LED), that converts electrical input signal into light, a closed optical channel (also called dielectrical channel, and a photo sensor, which detects incoming light and either generates electric energy directly, or modulates electric current flowing from an external power supply. The sensor can be a photoresistor, a photodiode, a phototransistor, a silicon-controlled rectifier (SCR) or a Triac. Because LEDs can sense light in addition to emitting it,construction of symmetrical, bidirectional opto-isolators is possible.
An optocoupled solid state relay contains a photodiode opto-isolator which drives a power switch, usually a complementary pair ofMOSFETs. A slotted optical switch contains a source of light and a sensor, but its optical channel is open, allowing modulation of light by external objects obstructing the path of light or reflecting light into thesensor.
OPTO COUPLER (4 Pin)
1. LED ANODE
2. LED CATHODE
3. PHOTO TRANSISTOR COLLECTOR
4. PHOTO TRANSISTOR EMITTER.
HOW TEST OPTO-COUPLER WITH DMM—SELECT DIODE MODE IN DMM OPTO-COUPLER TESTING: 6-PIN TYPE (DMM MEANS (DIGITAL MULTIMETER)
STEP-1:Connect DMM positive Red test lead to pin-1 (LED ANODE) Negative black lead to pin-2 (LED CATHODE) Display reading shows .983v (983 mV)
STEP-2. Connect DMM
Negative Black test lead to pin-1
positive red lead to pin-2
Display reading shows OL
Connect DMM positive Red test lead to pin-6 (BASE) Negative black lead to pin-5 = .618V (COLLECTOR) Negative black lead to pin-4 = .648V (EMITTER)
Display reading shows
STEP-3 .Connect DMM Negative Black test lead to pin-6 positive red lead to pin-5 positive red lead to pin-4
Display reading shows OL PIN -3 No connection (6 PIN TYPE OPTOCOUPLER)
Verification: If the DMM above reading shows the condition is GOOD Verification: If you get reading in forward bias as 0000 or OL or 1, and in reverse bias as 0000 (or) low values the opto coupler can beFAULTYand needs replacement.