Rsl5000 PID

pct_elect

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Join Date
Apr 2014
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PA
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I don't see anything in the reference manual, does anyone know if the Control Variable tag can be changed in the PID instruction so that I could just use one and switch it between two different analog outputs? (CWP_PID.CV?) Or is this bad juju and just go ahead and use another loop?
Thanks.
 
Without having very much info- Could you just use a MOV to move CWP_PID.CV based on some type of condition into one or the other analog output? Just remember, when you switch from one to the other, the last value will be stored in the non-used analog output until you overwrite it.
 
Sorry for lack of info. Manual does not show that .CV is available. I was wondering if anyone here new of a trick to be able to write to the Control Variable tag in the PID.
 
dginbuffalo method is the answer.

The address (Tag) you put in the PID instruction for it's CV does not have to be the address of your analog output card. It can be an internal address and then use dginbuffalo's method to move that value to whatever analog output card (or where ever) you want.
 
Of course the member tag .CV is available. "My_PID_Loop.CV". There are no hidden members in the PID or PIDE instructions.

Why would you want to write to it though?
If you must, the best way is to toggle on the .SWM (software manual) bit and write a value to the .SO (Set Output value).
 
I looked over the reference manual and there is no mention of .cv
(http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1756-rm003_-en-p.pdf) page 637.
This project has two pumps, one is redundant, that run to keep a tank pumped down (via VFD) to a set level. For simplicity of HMI presentation to the operator I thought it best to use one PID loop and just select which pump would do the work. Although it looks obvious now, Mickey's answer is certainly the way I think I should go.
 
The PID uses the .out instead of a .cv. The PIDE has a .cv and .cveu. The PIDE has a few more features, but it is only available in function blocks.
 

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