Technical assessment of novel digital impedance bridges able to calibrate a capacitance standard against a resistance standard in the frequency range around 1 kHz with an uncertainty lower than few parts in 10-7.
A travelling bridge from INRIM will be moved to the other partner sites; the comparison will be performed by verifying the compatibility of the calibration outcomes of the travelling bridge and the onsite bridge.
Progress Report 2021-10-12
The travelling INRIM’s electronic-digital impedance bridge has been moved to the PTB to be compared with the PTB’s Josephson-digital impedance bridge.
At the beginning of September 2021, the INRIM’s bridge was reassembled at PTB by the coordinator of the project and a preliminary technical assessment has been performed by verifying the compatibility of the calibration outcomes of the travelling bridge and the onsite bridge. The standards employed in the assessment are: two PTB’s 10 nF capacitance standards, an INRIM’s 8 nF capacitance standard and two 12.9 kΩ resistance standards, one from INRIM and one from PTB. The impedances are compared in R:R and R:C configurations with a 1:1 magnitude ratio to optimise the INRIM’s bridge accuracy. The working frequencies are chosen consequently (1233 Hz, 2466 Hz and 1541 Hz). The relative deviation between the calibrations performed with the INRIM’s and the PTB’s bridges are of few parts in 108 with a combined type A uncertainty of the same order, lower than the target one.
The comparison has been very fruitful since it allowed to discover issues in the INRIM’s bridge implementation. In particular, the current equalizers number, position and efficiency, the switches involved in the balance automatisation and temperature dependence of the digital signal source have been investigated. A further assessment of the performance of the bridges in the comparison of the impedance standards against the graphene ACQHR (quantum Hall Resistance in AC regime) is now ongoing.
Due to the pandemic restrictions, the comparison of the travelling INRIM’s bridge with the bridge of the second participating partner, METAS, has to be delayed and has not been scheduled yet. We expect to be able to perform the activity during the next year (2022) before the new proposed expected completion date, 31/12/2022.