VFD analog output offset.

Hi all,
I have a ABB ACS 550 VFD, and I'm reading current from the first analog output (AO1).
The range I'm using is 0 to 66 amp, 4 mA to 20 mA.
The issue is that I'm reading around 1.7 amp when the motor is stopped, when it should be 0 Amps.
Any thoughts?

Is the output putting out 4mA exactly? or possibly 4.2mA?

Also, the analog input might be scaled a little off.

Aabeck said:

Is the output putting out 4mA exactly? or possibly 4.2mA?

Click to expand...

The reading is around 4.4 mA when the motor is stopped.

Also, the analog input might be scaled a little off.

Click to expand...

I know I could scale it, but I don't usually have to do this. The VFD parameters seem to be correct, the wiring seems to be correct.

Elcan said:

The reading is around 4.4 mA when the motor is stopped.

Click to expand...

Not fluent in ABB VFD's but look through the parameter set and see if there are settings for the analog output

Something like:
0Hz = 4.4, 60Hz = 20

Sometimes these can be set to read for different frequency ranges (0-30, 0-50, 0-60, 0-400) and the minn value may have been changed.

If the minn value is set to 4 but getting 4.4 then try and set it to 3.6 and see if you get 4.0

Are you sure there is 0A in the motor? VFDs tend to send current to a motor even when it isn't moving, particularly if you are using sensorless vector control as it needs a level of magnetism in the motor to keep control of the speed, even at 0 Hz. If you were to disconnect the motor do you see 4.0 mA from your analog output?

Is there a signal conditioner or isolator in the circuit? If so they may not be perfectly calibrated.

Also, some VFD's can be configured to send a current through the motor when it is not moving in order to prevent condensation (e.g. overnight in areas with very humid conditions).

Why your ABB Drive AO might have 1.7amps at motor stop

Don't be worried as one of the suggested solutions would have been responsible for it.
Just to add to the aforementioned possible causes.

1) Sometimes, in addition to the fact that vector control keeps small current on a stopped motor. I also need to mention that in open loop V/F control, where the starting frequency could be anything above 0Hz to 6Hz... you would have some current on the AO output of the any VFD... this is to keep the effect of the starting frequency value on the stopped motor... Hence, if this is your case, what your are getting on the AO is normal and not a fault. So, do verify which control scheme you are using.

2) You may need to repeat your calibrations and set appropriate offsets as mentioned.

3) It's not out of place to check the integrity of your measuring instrument.

Pcontrols (Okoye)

Thank you for all the feedback, guys.
I am not currently in the field with the VFD, that's why I haven't replied yet.
There's no conditioner between the VFD analog output and the PLC analog input. We haven't checked the real motor amperage with a meter, neither.
I'll let you know as soon as I can get some feedback.