PIDE help

[dginbuffalo]

Hello all- I'm looking for some guidance on the attached PIDE setup. What I need the valve to do is be open 100% when the system is not running. I'm accomplishing this by the SEL block. When stopped, it uses In2 and moves 20,000. When running (after a time delay) it switches to In1 and takes the PIDE signal. My main question is how do I get the PIDE to take over from the 20,000 reference? Will holding CVPrevious at 20,000 accomplish this? The PIDE is going to want to shut the valve because its under pressure, but I need to hold it open for a time to get a loadless start and I want to have a bumpless transfer. Any suggestions? I know there are a lot of was to skin this cat. Thanks ahead.

 

[jamesau]

It looks like you should be close with what you have, provided the 'Recycle Valve Position Indication' (the input to CVPrevious) is scaled identically to CV (output).
You don't have the CVSetPrevious input pin visible; I think that should be set to 1.

The other way to skin this cat would be to use override mode (with ProgOverrideReq and CVOverride inputs). You could then eliminate the SEL block.

(It's been a while since I've worked with the PIDE). Good luck.

 

[danny.michael]

Use CVInit. When the system is down, set the CVInitReq (I believe that is the correct spelling, I do not have Logix 5000 handy). The CVInitValue should be scaled the same as CVEU. So set the CVInitValue to whatever you want out of the CVEU when CVInitReq is set. This allows the PIDE instruction to keep up with what's going on with the valve.

 

[dginbuffalo]

Thanks for the replies.

Jamesau- I do have the scaling the same and CVsetPrevious set to 1.

I did try to use the override mode and didn't have luck-not sure why? I have to look over it again but i assume override should over take any auto input correct? I'd like to use that method.

Danny- If you hold CVinitReq high does it continually move the initValue? and then release and the PIDE takes off from there?


Also- i'm assuming the PIDE must be enabled for any of these to work? I'm wondering if it's off if i can just write to the .CVEU also. limited rxperience with the PIDE function but it appears very robust!

 

[danny.michael]

Yes, when the CVInitReq pin is high, the CVInitValue is continuously moved to the output. You should always keep the PIDE enabled and manipulate the output via the provided inputs (CVInit, Override, etc.) so the instruction can keep up with what's going on. The instruction should also be operating in a periodic task.

I've never used the CVPrevious input but I believe if your valve is slow to move, feeding the valve position back into the CVPrevious input could cause some problems.