Powerflex 753 water pump application (pressure feedback loop)

I have a Powerflex 753 and want to control a water pump using the analog input on the main board. I have a current pressure transducer. If I use the Analog In P50 value as my speed reference, can I set the minimum at 20ma(or the min ma value that matches my maximum required water pressure) and the max at 4ma(or ma value that matches the minimum required water pressure) so that the drive increases speed as the pressure drops?

This would act as a feedback loop to slowly ramp up the pump speed to only what is necessary to maintain the water system pressure without using a separate PLC.

Thoughts?

I just tested this on a powerflex 525 and it worked with a current input. Automatically decreased speed as current increased. I'm guessing that it should also work with the 753.

To word it simply, does the analog input speed reference automatically invert if Analog in Lo is higher than Analog in Hi?

I'm not sure that is a good idea in the real world. It won't accommodate changing resistance to flow in the system. Many drives have built-in PID loops. I'd see if that is available on your model, use the analog input from the pressure transmiter as the measured vaiable and speed as the manipulated variable.

Tom Jenkins said:

I'm not sure that is a good idea in the real world. It won't accommodate changing resistance to flow in the system. Many drives have built-in PID loops. I'd see if that is available on your model, use the analog input from the pressure transmiter as the measured vaiable and speed as the manipulated variable.

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PID is built-in to the PF753 and Tom is correct, that's how you need to do it, otherwise the speed will just constantly "hunt" up and down and up and down. That's what a PID control loop does for you. You set an operating point (setpoint) that you want to maintain, in your case pressure, the PID loop varies the speed of the pump (control variable) to maintain that setpoint based on feedback from the pressure transmitter (process variable) while minimizing overshoot and excessive lag (undershoot) of the response.


If you have ever used the "Cruise Control" feature in a car, that's the principle of PID loop control.



Also yes, the Analog Input can be inverted. It's not "automatic" though, how would anything know to invert a signal automatically?

jraef said:

Also yes, the Analog Input can be inverted. It's not "automatic" though, how would anything know to invert a signal automatically?

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Powerflex 525 does this automatically, that's why I asked.

I'll read up on the PID function.