PLC

How it is used

The heart of most machines and lines, said letter by letter: P-L-C. You program, download to, go online with, monitor and back up a PLC. Engineers often name it by brand and family, for example a Siemens S7-1500 or an Allen-Bradley ControlLogix.

Example sentences

1. The PLC sends a start signal to the robot when the fixture is clamped.

2. Always back up the PLC program before you download any changes.

Common collocations

• program a PLC
• PLC program
• safety PLC
• go online with the PLC
• PLC rack

Related terms

• ladder logicA graphical PLC programming language that looks like an electrical relay diagram, with contacts and coils placed on horizontal lines called rungs between two vertical rails.
• I/OShort for inputs and outputs: the signals a controller receives from sensors and buttons, and the signals it sends to valves, motors, lamps and other devices.
• HMIShort for human-machine interface: the touch screen or panel operators use to see a machine's status, start and stop it, change settings and read alarms.
• scan cycleThe repeating loop a PLC runs: it reads all inputs, executes the program from top to bottom, then updates the outputs. The time one loop takes is the scan time.
• function blockA reusable piece of PLC code with its own inputs, outputs and memory, used to control one type of device, such as a motor, valve or conveyor, many times in a program.

More terms: PLCs and Industrial Control

• relay
• analog signal
• tag
• structured text