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The PU2/4 is a battery operated proving unit for testing the health of VI-13700/G, VI-16200 and MTL7 voltage indicators. The apparatus has been designed to tested in accordance with IEC publication 348, Safety Requirements for Electrical Measuring Apparatus. The PU2/PU4 employs the principle of switched stored energy transfer. When the probe ends of the testing device are inserted into the AC/DC output sockets an oscillating step-up transformer feeds energy from the battery to the load. The low battery voltage is switched on and off at a fast rate and transformed up to provide the required high voltage impulses necessary to fully illuminate all the neon lamps located within the testing devices. A high switching frequency is chosen to give maximum energy transfer and optimise battery life. When the probe ends of the testing device are withdrawn from the AC/DC output sockets the batteries are disconnected from the circuit and oscillation ceases.
