How to use a PID to control a PUMP Speed

dahmanishelly

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Join Date
Jun 2013
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Louisiana
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AB CompactLogix L32E Processor
RSLogix 5000 Version 20
Tank 100 is filled with liquid, a level transmitter LT-120 is installed on Tank 100 and its used as the sensor in the control loop.The Plc will send a 4-20mA signal to the pump to adjust the speed based on the level sensed by LT-120. High and Low set points will be used to control Pump 110.
Pump 110 has HOA(Hand-Off-Auto), I need to create a PID controllers to control the output to the pump based on the level set point. The level set point will initially be set to 50 but must be adjustable from an HMI. The speed of the pump will be controlled to maintain a level set point in the tank.
I already create pump110 Logic, PID and I scaled LT120 but in some how its not making the pump work in auto??
Any suggestions :confused:🤾

pump1.jpg 3.jpg 2.jpg PID.jpg
 
We pumping in the tank and controlling levels with LT120. and then pumping out the tank using pump 110 whenever LT120 sense a Low or a high Level.
 
Ok. What happens to the output of the PID when LT120 falls below the setpoint?

Just wondering if it might be a directional issue. You want it to run when the PV (LT120) is greater than the setpoint. By default, the control action is the other way. Something to look for, and really impossible to say without seeing the configuration of the PID.
 
We pumping in the tank and controlling levels with LT120. . .
Say what? Is Pump 110 pumping liquid INTO the tank at some times, and then pumping liquid OUT of the tank at other times?

I think that your Pump 110 logic is set up to only pump OUT of the tank. Pump 110 is only started when the Level Transmitter 120 Low is NOT LOW, and Level Transmitter 120 High is High, meaning that Pump 110 cannot fill but only empty the tank. Filling of the tank is not shown, and must be handled elsewhere.
 
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That's where I was getting the direction of Pump 110. No specific mention of how the tank is filled. It appears the same level sensor is involved in both the fill and drain processes.
 
Say what? Is Pump 110 pumping liquid INTO the tank at some times, and then pumping liquid OUT of the tank at other times?

I think that Pump 110 should be set up to only pump into the tank to control the tank level. Draining or disposal of the liquid should be handled by a drain valve or a second pump.

Pump X pumping liquid INTO Tank 100 and Pump 110 pumping liquid out the tank using LT120 as Sensor for Low and High level.
Sorry if i wasnt clear:wish:
 
Thanks, at least we know sort of what you are doing now. I had to figure it out by looking at your Pump 110 control logic. If you are using the same LT120 sensor to control the Fill Pump X, then that could be a problem.
 
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I already created the Pump 110 Logic and PID, and I scaled LT120, but somehow it's not making the pump work in Auto Mode. Why?
As Jordan has already pointed out, it may be that your PID is set incorrectly. Looking at your 2.JPG SCALE, your Level is now "85.78", but your Setpoint in the PID.jpg picture is only "75". If your are using the default "Reverse-acting" PID Logic, your Output would not go on. You need to set your PID block for "Direct-Acting" logic (Error = Process Variable - Setpoint).
Direct acting causes the output CV to increase when the input PV is larger than the setpoint SP (for example, a cooling application).
Rockwell Software
 
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