Glossary · Automation fundamentals, platforms and components
Optocoupler
Also known as: Optoisolator, Opto-isolator
German: Optokoppler
In electronics, an optocoupler is a component that transmits a signal between two electrically isolated circuits using light, typically an LED and a photodetector in one package.
- Automation components
In one sentence
An optocoupler transmits a signal between two electrically isolated circuits using light, typically from an LED to a photodetector.
Example
The digital inputs of an I/O module are optocoupler-isolated, so a voltage spike on the field wiring does not reach the controller's logic.
How it applies
- Engineering: Optocouplers provide galvanic isolation in digital I/O, communication interfaces and drive control. Isolation voltage and switching speed are key parameters.
- Maintenance: Aging LEDs reduce the current transfer ratio over years; this can matter in long-life equipment.
- Documentation: Data sheets should state isolation voltage and between which circuits isolation exists. Do not describe optocoupler isolation as protection against electric shock unless the device is rated and certified for that purpose.
- Commissioning: Input delay introduced by optocouplers and filters is part of the total signal response time.
Optocoupler vs. relay
A relay isolates with a mechanical contact and switches higher currents but wears. An optocoupler switches small signals fast and without wear. Solid-state relays combine an optocoupler input with a semiconductor output.