VFD & water pump

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ptonsparky

ptonsparky

Tom
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
I am still fairly new to VFDs and bought an inexpensive one a year or so ago just to get the feel. We set up a pair of Danfoss drives on a couple of wells for compressor cooling in a grocery store. They do everything you could want plus dispense paper.

The shop drive is giving me fits. When set up with a 0-10V input, on call the drive ramps to 60hz in 1 sec, then reduces to a min of 30 hz as I increase the votage to 10. What I want.

Put the 4-20ma pressure transducer in that will be used, and it will ramp to 30hz then increase speed as pressure goes up. Just backwards. A PID loop works but I thought it should be simpler.

Suggestions?

Thanks
 
Not sure.

The shop drive is from Automation Direct and it has a couple different ways of handling that. I think. One is 'Analog Input Offset Polarity' - worked for the 0-10v.

The other sets the PID feedback as 'Forward-acting', and that does work for the 4-20ma in a PID loop. Quite well.

I might add the Danfoss were installed about a year ago and have work beautifully.
 
ptonsparky said:
...
Put the 4-20ma pressure transducer in that will be used, and it will ramp to 30hz then increase speed as pressure goes up. Just backwards. A PID loop works but I thought it should be simpler.

Suggestions?

Thanks
Click to expand...
I don't quite understand your question. You said the PID works, so what's the problem? Are you trying to maintain a setpoint with just a transducer signal and no PI or PID loop? If so, adjust your thinking. You NEED a PI controller to maintain a setpoint, otherwise it will just hunt around all day long.
 
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