An audio device which displays a signal level in Volume Units is called a VU meter. This equipment is also called volume indicator. A characteristic VU scale is from -20 to +3. Generally the VU meter takes 300 milliseconds to reach the 0 on the scale if a constant sine wave of 0VU amplitude is applied abruptly. This means that the rise and fall time of the meter is 300 milliseconds. The VU meter is deliberately a slow measurement, which reproduce the apparent loudness of a material by averaging out peaks and troughs of small period. The VU meter was first used for the levels of telephone lines to measure and standardize them.
Step 1 – Hook up the Lines
This is the first step of testing a VU meter. Clasp the power lines and the signal generator lines.
Step 2 – Turn on Power Supply
After connecting the lines, turn the switch on of the signal generator and 1 KHz Sine Wave. Then put this signal to the third connection pad. Remember to attach the power supply source to the V+ and GND link pads.
Step 3 – Adjust Trimmer
After all these connections, adjust the trimmer resistors in such a way that when you provide a voltage from the signal generator to the VU meter, the LED lamp (third) lights up.
When the VU board will run, place your multimeter tester probe just in the center pads of the trimmer resistor. Now turn the top-screw head of the trimmer resistor. Stop when you find the voltage is at 0.775 volts.