MVP 2023 Ausman Posted April 18, 2015 MVP 2023 Report Share Posted April 18, 2015 Hi again all, I have been working on another brand of PLC lately and am now back to my Unitronics stuff. The other brand treats sequential "groups" of ladder work as part of the main scan. I spent hours yesterday trying to figure out why a linearisation wasn't working. I was developing the next stage of a program and just had one element in the ladder, to work from there. Double check everything and it should be working....hmmmm...why not? Maybe I've forgotten how to do the X/Y relationships. Change things around again, many many times and still no output to my MI. What is going on? Power is there and it all should be working. Finally in frustration I looked up other work and noted the subroutine calls. I hadn't put any into my ladder because of my using the other PLC type which didn't need them. I was simply doing the same thing, where I had a number of routines but had separated them into the general idea of what was happening in that part of the ladder. On the other PLC I didn't need to call them. In this case I was starting on all the linearisation that is going to happen, wth it all in its own subroutine. My big whinge is that Visilogic (9.7.0/0) shows the power rail as active across the ladder elements in a subroutine that isn't being called. This is what was constantly throwing me off. To my thinking this is a significant fault in the program. If I had seen that there wasn't any power I would have twigged immediately. But I was being told that it was there. I know that I should have realised my error, but it is easy to get confused when working with other PLCs, as one has to remember so many different ways of doing much the same thing. But having the power rail as showing didn't help at all!! And the other thing that really bugs me, which perhaps should be in a separate thread, is that you can't do even the most minor alterations to a program on line. This other brand lets it happen to a high stage of complexity. Whilst online you can enter an edit mode and use most of the elements available. It asks all the precautionary questions that one would expect when you tell it to commit, as I understand that in some instances such a capability has the possiblity of doing something catastrophic. However, used sensibly it is fantastic. It makes it so much easier to change your ladder when you have made a dumb error, or want to try another way. I wish Unitronics would try to find a way for this to happen......it is a right pain in the bum having to go through the entire download process if you just want to trial/change one tiny thing. cheers, Aus 1 Quote Link to comment Share on other sites More sharing options...
MVP 2023 Ausman Posted April 25, 2015 Author MVP 2023 Report Share Posted April 25, 2015 No comments as yet on this problem that I think needs resolving? I have tried the latest version and the issue is the same. If something isn't being called, it shouldn't be showing power. cheers, Aus Quote Link to comment Share on other sites More sharing options...
cantcliff Posted April 29, 2015 Report Share Posted April 29, 2015 Every class I've attended on PLC programming started out with the assumption the left power rail is always powered because PLCs are a digital version of hardware relay programming where you would always have that line powered. Even working with some of the Allen Bradley controllers I've seen the same issue you're talking about. Power always flows left to right through the rung, you use relays to control whether that power completes the circuit or not. You're thinking more like a software programming that a function call doesn't do anything within the function until it's called which isn't always handled the same way depending on the PLC manufacturer. Keep in mind subroutines are more for making the ladder program look better and help with the maintainability of the program but they are not needed. There is nothing you can do with a subroutine that could not be put in the main program ladder. Quote Link to comment Share on other sites More sharing options...
MVP 2023 Flex727 Posted April 29, 2015 MVP 2023 Report Share Posted April 29, 2015 Keep in mind that when you go online in VisiLogic it's really only reading the state of each memory location and highlighting it in the ladder (at least that is what it looks like to me). It doesn't check anything about the logic - in fact it doesn't even care if it's the same program in the PLC as what you're looking at on your PC. In VisiLogic, never assume the power flow logic represents reality in the PLC. All of that is changed with UniStream (and improved). Quote Link to comment Share on other sites More sharing options...
MVP 2023 Ausman Posted April 30, 2015 Author MVP 2023 Report Share Posted April 30, 2015 Thanks Cant and Flex. I hear your opinions and take note. Although no expert, I have been programming many brands of PLCs on and off for 20 years. I use the subroutine method purely to make it easier to work on the many different aspects of the installs I do. If I didn't break things up some of the ladders would be very large indeed! I try to follow the descending method of Inputs, process/adjust, interpret, anything ultra important happened since I started?, outputs. With many offshoots within each area being run as necessary. If the now-defunct "20 year old but still good" system that I was working with can show what the power rail is actually doing over a slow serial connection, I can't see why something more modern shouldn't be able to do it as well. I agree, Flex, that it just seems to show what each state is. Another example of the old system's logical design is that my "fast" timer issue by being called twice doesn't happen in this older gear either. If you set a timer running, it just bangs away correctly no matter how many times it is referenced or looped. Don't get me wrong, I love Unitronics gear. I re-accomodate to the different systems, but it just takes time to settle back into driving the different vehicle! cheers, Aus Quote Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted May 8, 2015 MVP 2023 Report Share Posted May 8, 2015 Unitronics has always shown the live power rail even on logic that's dead. It is what it is, and I agree it is very confusing. I, too, have many PLC brands under my belt. Maybe a comment from the Creators? Joe T. Quote Link to comment Share on other sites More sharing options...
Cara Bereck Levy Posted May 11, 2015 Report Share Posted May 11, 2015 I'm looking into it, guys Quote Link to comment Share on other sites More sharing options...
MVP 2023 Ausman Posted July 5, 2015 Author MVP 2023 Report Share Posted July 5, 2015 Hi Cara, Giving this a bump! Any answers? cheers, Aus Quote Link to comment Share on other sites More sharing options...
lawry Posted July 6, 2015 Report Share Posted July 6, 2015 My first rung in every subroutine is an Increment XDW. If this count is changing, it means that the subroutine is being serviced. When it does not change, i can ignore all the logic thats present in that subroutine Lawry Quote Link to comment Share on other sites More sharing options...
MVP 2023 Ausman Posted July 8, 2015 Author MVP 2023 Report Share Posted July 8, 2015 Hi Lawry, That's a useful idea and a good workaround. I have been working on the older system again and it still impresses me with it's very useful features. cheers, Aus Quote Link to comment Share on other sites More sharing options...
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