Practical Tips and Techniques
Scan of the PLC. Reading inputs, solving logic, setting outputs, communications, etc.
Logic circuits in a PLC ladder logic program are either on or off. The inputs change, which will affect the outputs. This can be expressed in a timing diagram. The timing diagram or chart will show you how the ladder logic program will respond to the changing states of the inputs and outputs. This visual … Read more
Normally open (NO) contacts or inputs in the PLC ladder logic program do not mean the same as a wired normally open switch. NO contacts on the ladder logic provide the logic condition for the rung to turn on the output. We will be looking at three things about the normally open (NO) contact on … Read more
The Productivity Suite Software allows us to modify our existing program and execute the new code without stopping the scanning of the PLC. This is referred to as online programming or editing. We change the ladder logic code and when we save it to the PLC, the current scan of the PLC is held until … Read more
The High-Speed Input Pulse Catch will set an output that can be seen by the PLC ladder logic scan in response to an input pulse. Inputs that are too fast to reliably be seen by the ladder logic scan time will be seen. The BRX Do-More series of programmable logic controllers have built-in high-speed inputs. … Read more
The productivity suite programming software has a debug mode. This will allow you to view and control the rung execution on your ladder logic code. These programming tools allow you to troubleshoot, find, and correct errors in the PLC programming logic. We will be adding a couple of rungs to our exiting start-stop circuit we … Read more
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. … Read more