Aspects of Application and Calibration of a Binary Compensation Unit for Cryogenic Current Comparator Setups

Abstract

We have developed a binary compensation unit for balancing measurement bridges with cryogenic current comparators (CCCs) commonly used in resistance metrology. We present the basic design ideas for the new microcontroller-operated module. It offers balance over a gapless range of resistance ratios of the resistors to be compared. The binary setup allows for convenient calibration when being combined with a binary CCC. The calibration can be performed using the CCC's control electronics and software. Examples of measurements demonstrate the unit's high flexibility and stability of resistance calibration well below one part in 10 9 over a period of 21 hours.

A compact 14-bit cryogenic current comparator

“…Examples include investigations of the fractional quantum Hall effect, the direct use of a CCC as a current amplifier [3] or alternative approaches with the CCC being used for an amplifier's calibration [2]. …”

“…However, in this case, there is not much benefit from the increased numbers of turns, because already for the 12-Bit-CCC experiment, the Type-A uncertainty is no longer dominated by the contribution related to the SQUID noise. Of course, all these experiments involved an auxiliary CCC winding of one turn in the primary circuit of the measurement bridge for achieving good balance [2].…”

Ultrastable low-noise current amplifier

“…It flows through a standard resistor R 2 , and the resulting voltage drop is measured with the bridge voltage detector. The demands on the accuracy of standard resistor R 2 are quite modest because the error signal is kept low (<1 ppm typically) by the binary compensation unit [15]. In case of a larger relative gain deviation, the turns ratio is adapted appropriately to relax the demands on the compensation unit.…”

“…The amplitude of the resulting low-frequency square wave yields the desired dc level. In this paper, raw data analysis according to the method sketched in figure 7 of [15] is used to determine the result of dc current measurements with the ULCA. To suppress settling effects after current reversal, a certain number of data points is disregarded after each polarity change.…”

“…Table 1 Φ 0 . The CCC bridge contribution summarizes all systematic uncertainties related to the experimental setup, e.g., the gain error of the bridge voltage detector and the ratio errors of the CCC windings and the binary compensation unit [15]. Table 1.…”