Which devices provide opto isolation between field device power and controller or motor drive system power?

• A. Input modules
• B. Output modules
• C. Both input and output modules
• D. Power supplies

Answer: (C)

Optical isolation uses light to transfer signals while keeping the electrical sides separate, shielding the controller from voltage spikes, noise, and ground potential differences on field wiring. This separation is essential for protecting sensitive controller electronics when dealing with motors, sensors, and other field devices.

Both input and output modules include opto-isolators. On input modules, a field signal from a sensor or device is fed through an optocoupler, so the controller sees an isolated version of that signal and the field power domain is kept apart from the controller’s power. On output modules, the controller drives an opto-isolator, which then switches the field-side device, again keeping the controller’s power isolated from the high-power field side.

Power supplies, by contrast, provide the necessary operating voltages but do not inherently isolate the field power from the controller unless a specially designed isolated converter is used. So the devices that provide opto isolation between field device power and controller or motor drive power are the input and output modules.