So how do programmable logic devices work?
All PLC applications feature a CPU, inputs, a program, and outputs. The inputs are detected by the PLC. Input types vary. They can be discrete inputs such as whether a switch is ‘on’ or ‘off,’ or opened / closed readings for valves or pumps. Alternatively, they may be analogue inputs that reflect a range of values. Temperature and pressure, for example, provide analogue inputs.
Human input comes from machinery operators. It might include pushing buttons or touchscreens, making keystrokes on a keyboard, or flicking a switch. The other source of input data for a PLC might be an operator of an HMI or SCADA system.
Based on the information the PLC receives via its input, the PLC programming executes and operates output devices, which might include actuators, valves, or human-machine interface displays. PLC outputs can include audible or visual indicators such as alarms or beacons. Other outputs may be changing motor speed or opening or closing a valve.
As part of its programming for processing inputs, the PLC will also undertake a quick health check to ensure the system is working within normal parameters. Once that’s complete, the manufacturing cycle restarts.