In ladder logic, what is used with inputs and outputs to formulate the desired control operations?

• A. Signals
• B. Logic Expressions
• C. Timers
• D. Process Variables

Answer: (B)

In ladder logic, you express when an output should energize by building a logic expression from the inputs. Each rung evaluates a boolean condition: inputs (represented by contacts) are arranged in series or in parallel to form the required logic. If the combined condition is true, the output coil on that rung is energized. Series connections implement AND behavior (all conditions must be true), while parallel connections implement OR behavior (any true condition can energize the output). Inverting a signal can be done with normally closed contacts, giving NOT-like behavior within the expression.

This approach—combining inputs to form a logical expression that drives the output—is what the control operation relies on. Signals are the actual input/output values used within those expressions, timers are specific timing functions, and process variables are broader state indicators—useful concepts, but not the general mechanism for formulating the control logic itself.