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Conor

PLC 5 PID Instruction

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Hi guys, I have a new PowerFlex 40 that is connected to a PLC 5 on DeviceNet. I have the drive set-up on the DeviceNet and am able to read/write from it. I am trying to set-up a PID to set the output on the drive. This is based on an Analogue Input from a pressure switch. I have set-up the PID, but am having a bit of trouble to get it working as I would like. I have attached a word doc with some screendumps. F8:99 is my Pressure Scalle 0 - 10.66 bar I am able to MOV this into PD27:6.PV as you can see, but when I go to run the PID it uses Process Variable N13:212. If I put in a zero to N13:212 then the PV is not taken from the line above? I had originally did a MOV from F8:99 into N13:212. As can be seen from the screendump I tried to use PD27:6.PV in place of N13:212, but got an error (screendump). From the error I take it that I need to use a Word value i.e. N13:212. I have also added the PID config in the screendump. Thanks, Conor pid_pv.doc

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You use an integer for the process variable input ( which can come directly from your analog input card) to the PID instruction scaled 0-4095. You then use the engineering unit min/max settings to scale that input to engineering units ( which you have done 0-10) Sense you have a update time of 1 sec you need a XIC -| |- instruction upstream of the PID instruction that pulses every 1 sec. This is usually done with a timer done bit. The PD27:6.PV is used to display the scaled value of the PV in engineering units. In your case 0-10. See PDF for PID Manual PIDmanual.pdf Edited by Mickey

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Thaks for that Mickey. I wasn't sure about the timer. So I need a .DN bit from a timer at the start of the rung that the PID is on? I thought that the 1 sec in the PID instruction would do. The PD27:6.PV would be used to diaplay values on a Scada or the likes? Conor

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Yes The PID manual I posted above was incomplete, I have corrected that. Edited by Mickey

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