Calibration of 100 Mohm Hamon resistor using current-sensing Wheatstone bridge
Ivan Leniček, Roman Malarić, Alan Šala · 2004
Primary electromagnetic laboratory in Zagreb maintains standards of four major electromagnetic units: volt, farad, ohm and second. Reference standards are periodically calibrated in PTB (Germany) and several methods has been realized for internal laboratory traceability check. RC-comparison method uses Hamon divider constructed of 100 equally balanced 1-megaohm resistors that connected in parallel or serially exhibit Hamon ratio of 100 Mohm : 10 kohm with relative uncertainty of 10-8. Hamon resistance of 100 Mohm is directly compared with impedance of 100 pF capacitance reference at frequency of 15, 873 Hz. Measurement of low-frequency voltage ratio is based on two digital voltmeters HP 3458A with improved algorithm for data processing. Accuracy of reference standards comparison 10 kohm - 100 pF depends on consistency of Hamon divider that can be disturbed by aging of used metal-film components. In this paper a recently realized method for accurate measurement of 100 Mohm Hamon resistor by means of comparison with calibrated and stable 10 Mohm resistance standard at higher voltage levels has been presented.