The new Megger MPU690 Proving Unit provides a portable, battery powered voltage source that can verify the correct functioning of a voltage tester. The MPU690 safely generates a range of voltages from 50V to 690V in five steps. When switched on the MPU 690 proving device will initially generate 690 volts and after a short period will slowly ramp down through each voltage step until the unit switches off. Each individual voltage step is indicated by an LED with one for indicating power that also indicates exhausted battery. The Megger MPU690 will automatically power up when voltage tester probes are inserted into the output terminals, generating a 50Hz output voltage which simulates the AC mains supply.