VFD controlled from 4/20ma 1

[powersoff]

I have a Altivar 21 VFD that I would like to use to control a pump. The vfd needs to run based on a 4/20ma input from a transducer directly to the drive. 14ma means the tank is full and the pump should run to avoid overfilling the tank. 4ma means the tank is empty and the pump needs to shut off to avoid sucking air. The tank takes about a half hour to fill and 5 minutes to empty.Does anyone have any advice?

 

[ozmosis]

What about using the 4-20mA signal as a feedback and using the built in PI control to maintain a constant level in the tank. Set your setpoint to something like 9mA and the VFD will try to maintain a constant level.

 

[ozmosis]

Actually, there is an easier solution with the Altivar 21 in open loop (not using the PI control). Parameters F241 and F242 provide a means to stop the drive when the analogue reference signal goes below a certain level (this would be your 4mA) and then F242 provides a hysterisis so that when the signal comes back above 4mA + your hysterisis, then it will restart. Your 14mA could be set to the FH (maximumum frequency setting). In this way the VFD would function like a simple thermostat with a starting hysterisis to prevent constant stop/starting at low level.

 

[powersoff]

Thanks for the reply ozmosis.
I am not sure I understand the part about setting the 14ma to the (FH) max freq ?

 

[ozmosis]

FH is maximum frequency, the parameter is shown on the drive as "FH". It's like an electronic limit stop.
Attached is the section out of the manual that explains the (2nd) process.
I haven't used it myself as Schneider are actually one of our main competitors but hey, this is Eng-Tips..

 

[controlsdude]

schieder and square d are the same thing, and avitar or altavar is a the low end of the vd manufacturers.

I remember sitting in this meeting with the rep and did not know the product. wish I had that time back.

 

[powersoff]

Many thanks ozmosis.
Friday I spent over an hour on the phone with tech support and was not able to get such clear and concise information.

 

[ozmosis]

You're welcome. I'll send them a bill..I'm sure they'd love to see it from the large Danish drives company I work for!