Alex_Sh

@PLCMentor.com this sounds like a great approach.

We have been working with PLCs for long time. We used to develop PLC logic, partly test it on an emulator and test the rest on the partly energised equipment. From time to time working with computer software development (C# and JavaScript) I was always looking for something similar to unit testing in the PLC world. As I couldn't find anything at that time I've started developing own automated testing tool. Now we use this tool, which basically simulates PLC inputs in defined actions and checks expected behaviour of internal tags or/and PLC outputs. If it behaved the way we expected, it's PASS, otherwise it's FAIL. We break complex logic into small parts and create unit tests for it. By creating more of these unit tests we can test PLC logic of any complexity. The software called PLC Logic Prover and it's free at https://www.controlx.io Recently, I've been told that there is no point to develop anything new if there are already great tools on the market. Honestly, I didn't do proper research earlier, so I'm here asking the experts. What do you use to test PLC logic? What automated testing tools do you use? Is it using IO simulation or it can test logic by other means? Your replies are appreciated. Thanks, Alex

@PLCMentor.com do you run test/simulation only on the completion of the PLC logic development? What if you have done changes after the simulation, do you do the tests again? Or you test only the changes?

@Izzybe I appreciate this. This is what I'm looking for, the different approaches in improving my PLC logic development.

@Joe E. this is how we used to test our PLC logic. We even had the same approach for complex machines or processes, however it becomes messy and testing logic become too messy. @Izzybe thanks for suggestion with the simulation packages. However, it seems like these packages are more about the plant simulation, not a simple PLC logic testing.  

Thanks @ElectronGuru The stage you described we call commissioning. Yes we check the inputs and outputs as it is part of getting the equipment up and running safely. However we prefer conduct as much testing as possible before the commissioning. We download the program into a bench PLC and run tests. Mostly the PLC has no IO cards or if it has we just inhibit them. And we run specially developed software with predefined test cases. Try our free software from https://www.controlx.io  I've been told that there are plenty of testing tools and I should stop the software development. So I'm trying find out more about the emulator and other 3rd party software tools. Thanks for your replies.

When you developed part of the code, uploaded it to the PLC and ready for testing, do you do it manually by creating a simulation logic and toggling (CTRL+T) its bits? Have you ever used any 3rd party software for IO simulation such as opcs, kepware, etc... mentioned by @Izzybe  above?

Thanks ElectronGuru. Yes, Test mode is great option, if you don't want to have your outputs to go crazy on the first run on the real machine  (it doesn't not happen all the time, once one output was flickering due to simultaneous latch and unlatch in the code) Do you test PLC logic mostly on the emulator or on the real PLC in the Test mode?    

Yes it does, tanks Izzybe. Can you elaborate on Allen Bradley emulator, I haven't used it much. Can it trigger digital inputs and write to analog ones? In a pre-defined sequence like S7-PLCSIM from Siemens? We used the second approach all the time. Running the main program on the actual PLC, which usually goes to the client in the end of project development. While having a spare one with testing routines, connected to the production PLC over Ethernet. Have you used any 3rd party software? Can you recommend any? (thanks for the links to other posts with similar topics)

9 years later...  there is software does exactly as you described. PLC Logic Prover at https://www.controlx.io It is free, but the guys are looking for a sponsor to increase software functionality.