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Old August 11th, 2007, 03:50 AM   #1
PLC_talk
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How to set tuning constants for SLC PID loop

Hello,
I am using a AB SLC5/05 PLC & using the PID insrtuction for a single loop control. I have assigned N10:0 as the control block starting address, so I beleive the Kp,Ti,Td will be N10:3,N1-:4,N10:5 resp.
Question - The tuning constant are in decimal values where as the Integer file N10:x will not accept decimal. So how do I send the decimal constant to the PID instruction from the graphics screen?
Any pointer or solutions in right direction will be helpful.

Thanks,
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Old August 11th, 2007, 05:54 AM   #2
Drippin
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Maybe helpful.......

Are you entering values from an HMI? If not, you should just be able to double-click on the PID instruction "Setup Screen" and enter the values directly - here it would not matter if they were decimal fractions or integers.

If you are using an HMI to enter Kc, Ti and Td, well I'm not too sure about this as I have never done in SLC500 (PLC5 used Floating Point files and relabelled them in the file structure e.g. F18:0 becomes PD18:0). Looking at some software we use here it appears that the SLC500 performs a floating point-to-integer conversion if FP vales are enetered via a MOV instruction. Why not try entering some "dummy" code at the end of a running program to see how the PID instruction handles moved FP values?

Hope this is (a little bit) helpful!

Dave
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Old August 11th, 2007, 10:14 AM   #3
Mickey
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See links below. The values you write to the integers will have to be an implied decimal. The PID instruction has build in multipliers.

http://www.plctalk.net/qanda/showthr...ghlight=RG+bit

http://www.plctalk.net/qanda/showthr...ghlight=RG+bit
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Old August 13th, 2007, 08:25 AM   #4
PLC_talk
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Smile

Mikey,
Thanks, you were spot on

It solves my problem.

Regards
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Old August 13th, 2007, 09:41 AM   #5
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Your welcome
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