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PID control Analog output

Dave M

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Thanks for your reply! I have downloaded the example files. I have the USP-156-B10 PLC with analog input and output modules as well as transistor modules. I have successfully programed these units to use the PID function to control heaters with PWM using the transistor output. (like in the example files).  I want to use the PID control to vary an analog (4-20mA) output as a signal to a VFD to control a pump. 



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I would use the analog output value, set in your program, as the PID's Control Value; and take as its Process Value whatever measurement you are using to determine the effect of the pump, and its relation to the Set Point (also defined in your program).



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  • MVP 2023

Kind of.  But yes.

Typically I program the output of the block to range from 0-1000 which is easy to read as 0-100.0% and can be mapped into a PWM converter.

You can change the output of the PID block to match the D/A resolution of whichever analog module you are using, but I would personally leave the PID at 0-1000 and add a linear block to convert to what the analog output is expecting.


Joe T.

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  • 2 weeks later...

I still haven't sorted this out...

How do I change the output of the PID block? Setting the high and low limits? Also, my control value seems to stay at zero regardless of the PV and setpoint. I have attached the program for your review. The issue is with the PID_Feedpump ladder. 





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