A PC is connected to a data acquisition card which has single ended channels. One of the channels is outputting a constant DC voltage which can be controlled by a user via a program in the PC.
The output voltage is feeding a VFD. The VFD takes the voltage value and controls the frequency of the AC motor depending on the voltage applied.
There is an isolation amplifier between DAQ analog output and the VFD as in the figure. When I measure the analog output of the DAQ and the output of the isolation amplifier with a voltmeter I see the same value.
What might be the reason then for the isolation amplifier?