Modsoft Conversion Help

[Jeremiah]

Hello, I am faced with the task of coverting a modsoft ver 2.4 program over to an allen bradley plc. The program is currently running our waste water treatment facility. The processor is a 984-381E with about 30 outputs and 20 inputs along with some analog ins and outs it is 219 rungs. I would like to just convert the logic over exactly but am having a hard time figuring out the modsoft logic. Does anybody have any suggestions or help about the easiest way of doing so? Or does anybody have any experiences with an outside company doing modosft to rs500 coversions? Any help would be appreciated. Thanks for your time. Jeremiah Sells

[plcken]

It doesn't sound like a huge system - your IO count is pretty low, and 984 logic tends to get big quick. Without looking at the program it would be hard to guess exactly what you'll run into, but as a start: The ladder is scanned in a serpentine fashion. Normally that's not an issue, but I've seen 'clever' programmers use that do to 'tricky' things, things that break when you move them to an AB (or other) platform. That needs to be in the back of your mind all of the time. The counters and timers are pretty straightforward - top rung times/counts , bottom rung enables (on = time/count, off = reset to zero). The bottom rung of a timer will pass power EVEN IF IT ISN'T CONNECTED TO THE POWER RAIL - I've seen 'clever' people use that for 'tricky' things, so you have to watch that. Positive (and negative) transition contacts don't have a direct equivalent in a RS500 system - you'll have to build your own. The OSR isn't exactly the same thing. The SUB block might be subtracting two numbers, but it's far more likely to be there as a test block - top output is A>B, middle is A=B, and bottom is true on A<B. There's lots more things to know, but it depends on what the existing program has in it. Out of curiosity, where is the plant at? Ken

[Crossbow]

Get your hands on the Modicon Ladder Logic Block Library manual. It details all of the block instructions in the old 984 ladder logic language. Should be easy to determine a similar instruction if you are familiar with the AB. I'm pretty sure it's in the downloads section here, or you can get at www.telemecanique.com