Industrial Maintenance Technician Practice Test

Discrete inputs and outputs in a Programmable Logic Controller (PLC) are described as either ON or OFF because they represent two distinct states that a system or process can be in. This binary nature is fundamental to digital electronics, where discrete signals correspond to specific conditions.

In the context of PLCs, discrete inputs typically refer to sensors or switches that detect specific events, such as an object being present (ON) or absent (OFF), while discrete outputs control devices like relays or lights that can also be in one of two states: activated (ON) or deactivated (OFF).

This distinction is essential in industrial automation and control systems because it allows for clear and straightforward decision-making processes based on the discrete state of various inputs and outputs. The other options refer to continuous or variable signals, which do not accurately describe the binary nature of discrete inputs and outputs in a PLC environment.