27.11.2015
The "Ultrastable Low-noise Current Amplifier"(ULCA), developed at PTB and being commercially available soon, allows the traceable measurement and generation of small electrical dc currents at an outstanding level of precision.
The "Ultrastable Low-noise Current Amplifier"(ULCA, see also scientific news from 28.11.2014(only in German)), developed at PTB and being commercially available soon, allows the traceable measurement and generation of small electrical dc currents at an outstanding level of precision. The new precision instrument enables improvements in metrology fields deploying currents in the pico- and nanoampere range.
The non-cryogenic, handy instrument concept (applied for patent) was developed within the European joint research project "Qu-Ampere". Originally, the concept aimed at a new low-noise picoamperemeter, implemented as a two-stage transresistance amplifier with an effective transresistance of 1 GΩ with highest stability and linearity ("Ultrastable low-noise current amplifier: a novel device for measuring small electric currents with high accuracy", D. Drung, C. Krause, U. Becker, H. Scherer, F. J. Ahlers, Rev. Sci. Instrum. 86, 024703 (2015)). However, the ULCA also allows the traceable generation of small currents and the calibration of high resistances.
A central component for the calibration of the ULCA is a cryogenic current comparator (CCC) with binary design, newly developed at PTB. This CCC enables the traceable calibration of the ULCA with a relative uncertainty of less than one part in ten millions. Together with the high stability of the ULCA’s transresistance with respect to time, temperature and current amplitude (dynamic range ±5 nA), the measurement and generation of dc currents at outstanding precision becomes possible. A current of 100 pA, for instance, can be measured with a relative uncertainty of one part in ten millions within about ten hours.
The characterisation of the new CCC system, the application capabilities of the ULCA, and the resulting possible improvements in the field of small current metrology were in the focus of a study that is now accepted for publication ("Improving the traceable measurement and generation of small direct currents", D. Drung, M. Götz, E. Pesel, H. Scherer, accepted for publication in IEEE Trans. Instr. Meas. (2015)).
The ULCA together with the CCC system for its calibration are expected to become central elements in PTB’s traceability chains for small dc currents and high resistances in the near future.
Picture 1: Prototype of a two-channel ULCA (front view of the housing with SMA connectors)
Picture 2: 14 bit CCC system for calibration of the ULCA