Methods for the calibration of the input stage ('current ratio', input current 13 nA amplified by factor 1000) and the output stage ('transresistance', 1 MOhm feedback resistor) of the ULCA are investigated. The measurements aim on the comparative determination of the overall 1 GOhm transresistance of an ULCA by means of METAS or PTB setups on site. For that purpose, PTB's 12-bit CCC bridge setup is operated at METAS.
Final Report 2018-09-18
Two fully independent traceability chains have been realised. The calibration values of the input and output stages of two ULCAs agree within the measurement uncertainty. A manuscript for publication is in progress - its submission is expected by the end of 2018.