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Pete Moss

Powerflex 523 PID

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I am attempting to program a PF523 using PID exclusive control. I've read several documents on this issue, but am uncertain how to accomplish this. I have a grinder operation with a feed conveyor; I want to use the PID function to control the feed conveyor rate based on the grinder amperage. I've installed CT with 0-5 volt secondary; primary is 0-400amp.  This signal is connected to a 4-20ma converter. I'm using CCW to program the drive. I need the conveyor to feed at full speed from 0 to 150 amps and then ramp down to zero if the amperage reaches 200 amps. Ideally I'd like to maintain a feed rate resulting in about 175 amps on the grinder motor

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Was this a working system before the attempt to add PID control?  Where are you at with the process change - what is the change not doing properly?

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Currently the system utilizes a current relay to stop the feed conveyor at 200 AMPS, the CT is failing and needs replaced. The feed conveyor motor is served via the PF523, which does have PID control. My thought is to get a CT with 4-20ma output to drive the PID controller and regulate the feed conveyor speed. i set p047 to PID1 output - p458 to disabled for exclusive control - p459 to PID setpoint - p460 to 4-20ma input - p464 to 50% (PID1 setpoint). Looks like I need a 24vdc power supply for loop power in series with the 4-20ma CT

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Doable, but you've got some limitations.  The drive will accept a 0-10V signal.  You can scale that to CT's 0-5V signal. 

Your setpoint will be full speed at 175A. (You say 0-150A, then you finished with 175A, I'll go with 175A).  Any current above 175A on the grinder and you want the motor to slow down.  If the motor needs to ramp to 0Hz, that's ok, it'll set there until the grinder amps come down.  Be sure to adjust your acceleration to not slam to the grinder as my guess is the grinder current will come down dramatically. 

Your feedback, the CT, is 0-400A for the 0-5V.  That's not going to give you much resolution since you're somewhat defining your top acceptable limit as 200A.  With your setpoint at 175A, that only really gives you .31V (6%or of control range.  The closer your feedback sensor matches your actual process, in this case 0-200A, the better.  I think you can still achieve better results with the CT and PID than stopping and starting with the relay, but it'll be highly dependent on setting up your acceleration and decal to match your process feedrate.  

I'd use trim control, set P458 to 5 (0-10V).  That way you can set your speed reference for full speed, then set your PID setpoint for the V level that corresponds to 175A.  Anything above that and the PID will 'trim' down the speed.  Whereever you're setting your running speed (ie, keypad, preselected freq, etc.) set that to A471.  For the feedback, to use just your 0-5V CT, set A472 to 0.  Set t091(low ref) to 175A in the 0-5V scale: 43% and set t092 (high ref) to 400A in the 0-5V scale: 100%. 

Edited by AGill

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I mistated the CT, it is 0-5 amp and not 0-5 volt. My thought is to replace this with 4 to 20ma CT and connect directly to the PF523 4-20ma analog in point. We want to stop the infeed when we reach 200 AMP, my idea is to begin ramping down after 150 amp and stop somewhere around the 200 mark. PF523 does not have two PID loops, therefore no A471 nor A472.

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