AOI / reusable instruction: A vendor-specific or general reusable logic construct that packages behavior for repeated use.
Analog input: An input representing a range of values rather than simply on/off.
Commissioning: The process of testing and putting equipment into service against design requirements.
Common: The electrical reference or return used by a control circuit; meaning depends on circuit design.
Contactor: An electrically controlled switching device commonly used for motors and other power loads.
Controller tag: A named data item stored in a PLC project.
Digital input: A discrete on/off signal entering a controller.
Digital output: A discrete on/off command leaving a controller.
E-stop: Emergency stop function intended to reduce risk in an emergency; part of a safety system, not a normal production stop.
Feedback: A signal indicating what actually happened after a command, such as motor running or valve open.
Force: A software mechanism that overrides normal controller data or I/O behavior for testing/troubleshooting; must be tightly controlled.
HMI: Human-machine interface used by operators or technicians to view status and issue commands.
Interlock: A condition that prevents an action because another state makes it inappropriate or unsafe.
I/O: Inputs and outputs connecting a controller to field devices.
Ladder logic: A graphical PLC language inspired by relay control diagrams.
Permissive: A condition that must be satisfied before an action is allowed.
PLC: Programmable logic controller, an industrial controller designed for deterministic machine/process control.
Remote I/O: I/O located away from the main controller and connected through a communication network.
Scan cycle: The repeated execution process by which a PLC updates data, executes logic, communications, and outputs according to its architecture.
Sequence of operation: A plain-language description of what a machine does and under what conditions.
State machine: A method of organizing control into explicit operating states with defined transitions.
VFD: Variable frequency drive used to control AC motor speed and torque by adjusting electrical output to the motor.