In this direct reading digital High Voltage meter, a fully encapsulated input potential divider chain, using precision HV resistors of extremely high value, feeds a digital voltmeter module of high input resistance. Two ranges are provided: 0-20kV with 10V resolution and 0-40kV with 100V resolution. This gives a dc voltage measuring instrument with an accuracy of better than 0.25% which loads the circuit under test by less than 2ľA at the highest input voltage.

The meter provides accurate, high resolution measurement of high voltages over a wide range of values, with extremely low circuit loading. Positive and negative voltages may be measured without the need for switching. The digital meter Model 139 offers greater accuracy and higher resolution than the analogue meters Models 88 and 109, but with a higher current drain on the circuit under test.

The HV meter is battery operated and has a single control: a 20kV/40kV range selector switch with an OFF position. The DVM module itself incorporates low-battery indication. A precision recorder output is provided at 10mV per kV of input. The meter may be angled for convenience of reading when on a bench, and is housed in a metal case. The HV connection is made to a fully insulated socket with moulded polythene shroud. A mating screw-in connector with 2m lead, fitted with a 40kV hand-held probe, is supplied as standard. Other connectors are available.