Do I need a feedback card to acquire motor RPM from a VFD?

belae1ka said:

The VFD I plan on using;
DURApulse GS3 series AC drive: https://www.automationdirect.com/static/specs/gs3drives.pdf
Model: GS3-22P0

The feedback card accessory for the VFD: https://www.automationdirect.com/static/specs/gs3fb.pdf

Hi everyone, I would like to know if I need this feedback card to obtain RPM of a motor that is being wired using the VFD specified above. I plan on controlling a 3 phase motor with the program Labview. I will be using MODBUS to communicate between the VFD and Labview.

The end goal of my project is to plot the force of a load cell with respect to an increasing motor RPM so I was wondering how to get the RPM feedback from the motor. What exactly is the main purpose of this feedback card? In what kind of applications would this card be needed?

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g.mccormick said:

The feedback card is to wire a shaft mounted encoder back to the vfd. This will serve as the feedback for the vfd speed control. Without an encoer, the vfd should control shaft speed to within a fedw rpm. With encoder feedback, the vfd should be controlling speed to within 0.5 rpm.

If you are reading/writing values via modbus, you should get motor speed regardless of if the vfd had feedback or not.

For the GS3 drive.
Write value for requeste hz = Register 2331 (integer)

Read motor RPM = Register 8456 (integer)

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