What is an interlock in PLCs?

• A. A function that makes the state of 2 mechanisms or functions mutually dependent
• B. A timer function
• C. A safety relay
• D. A data logger

Answer: (A)

An interlock in PLCs is a control arrangement where the operation of one function or device depends on the state of another, so certain actions can only occur if a companion condition is met. This creates mutually dependent states that prevent unsafe or undesired operation. For example, a machine cannot start if a guard door is open—the door switch must indicate closed before the start signal is allowed. This is about conditional enablement and sequencing, not about timing alone, data logging, or a safety relay acting by itself. A timer simply delays or triggers events after a set interval, a safety relay provides hardware-level safety protection, and a data logger records data. So the best description is the mutual dependence of two mechanisms or functions.