In a ladder logic control circuit, the signal measured is usually what?

In a ladder logic control circuit, the signal measured is typically voltage. Ladder logic is a representation used in programmable logic controllers (PLCs) where the control system is often monitored and manipulated through voltages that signify the state of inputs and outputs.

When a device is connected to a PLC, it usually operates in a binary state; for instance, an input sensor may output a voltage level that represents either an "on" (typically +24V) or "off" (0V) condition. This voltage level is what the control system interprets to either trigger an action or maintain its current state within the ladder diagram configuration.

Other forms of measurement, such as current or power, may be important in different contexts or specific applications but are not primarily used as the standard signal in ladder logic circuits for control purposes. Ladder logic focuses on the logic states represented by voltage levels, which directly correlate with the input and output conditions of the system being controlled.