Self Calibrating High Voltage Divider

Abstract

High voltage calibrations on metrology level require traceability down to primary national reference standards. These standards are based on the Josephson effect, hence the maximum voltage is limited to less than 10 V. To transfer these reference voltages to several hundreds of kilovolts different reference dividers are required. Several intermediate steps are needed to utilize the optimal measuring range of the utilized dividers and voltmeters. The drawback of using several dividers is the increase of measurement uncertainty within each intermediate step. Additionally, the time required for traditional traceable calibration of the high voltage reference dividers can easily exceed several weeks. Since the PTB is one of the world’s leading metrology institutes it has started the development of a new high voltage divider design. This new development includes a high voltage arm, very similar to a standard high voltage divider. However, it is possible to connect all high voltage resistors in parallel. In this parallel arrangement the scale factor can be adjusted and compared to the primary reference standard. The adjustment is implemented by including a second precision divider that is only used at low voltages below 50 V. With the aid of a Wheatstone bridge arrangement these two voltage dividers are compared to each other. The adjustment is carried out with the aid of two potentiometers. One of the potentiometers is placed in the second divider to create a precisely known scale factor. The bridge is zeroed by a potentiometer in the high voltage arm. Thus, the known scale factor of the second divider is transmitted onto the high voltage divider. After finishing the adjustment, the parallel arrangement is changed back to series for the high voltage mode. Thereby, the scale factor is set to a calculable precise value. The divider that was built as a first prototype was compared to the existing reference divider and the results are shown within this paper.