The voltage that control a V/F converters will be displayed if we use a frequency counter, which is directly proportional to the input voltage. A 1 second time base will give 4 digit resolution with 1 reading per second when the V/F converters is running at 10KHz full scale.

4 DIGIT VOLTMETER WITH OPTOISOLATED INPUT circuit schematic

To transmit the frequency, we can use the optoisolator, so there is no DC path to the frequency counter. This will be useful in medical applications where a voltage probe should not be directly connected to the human body. [System’s block diagram source: Microchip Application Note]