In modular PLC discrete outputs, which type provides mechanical contact switching?

• A. Solid state AC
• B. Solid state DC
• C. Relay contact
• D. Analog

Answer: (C)

Mechanical contact switching comes from a relay-type output. In a modular PLC, a relay output uses a coil to move a physical set of contacts that open or close the load circuit. Energizing the coil pulls the contacts together to complete the circuit; de-energizing allows springs to separate them and open the circuit. This creates a true physical switch with galvanic isolation between the control and load sides. Solid-state outputs switch with semiconductor devices and have no moving parts, offering fast operation but with leakage, a voltage drop, and different load characteristics. Analog outputs, on the other hand, provide a variable signal rather than a discrete on/off contact.