Inputs Outputs PLC PLC Basics PLC Learning Productivity Suite Scan

PLC Learning Series – Program Cyclic Scan

Programmable logic controllers (PLC) use a cyclic scan. The time that it takes to complete one scan is called Scan Time. Typical scan times range from 10 milliseconds to 10 microseconds. This translates from 0.01 to 0.0001 seconds per PLC scan. Understanding how the program scan will help us in programming and troubleshooting the PLC.
The simplest scan cycle of a PLC consists of 4 steps. Read inputs, execute program, diagnostics, and communication, and update outputs.
We will be looking at each of these steps in a little more detail as we discuss the PLC program cyclic scan. Let’s get started.

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PLC Learning Series – What are Outputs?

PLC outputs are the next component of our PLC block diagram. The PLC program will control the outputs of the PLC. Controlling outputs is one way to get the inputs to change. We will be looking at digital and analog outputs that can be wired to the programmable logic controller.
PLC Learning Series - What are Outputs?

PLC troubleshooting outputs will also be discussed. This will be done using a multimeter measuring the voltage at the PLC output and across the discrete output load. We will also measure and control analog signal output. Let’s get started.