Direct comparison of two NIST PJVS systems at 10 V

Abstract

Two NIST programmable Josephson voltage standard (PJVS) systems are directly compared at 10 V using different nanovoltmeters. These PJVS systems use arrays of triple-stacked superconducting niobium Josephson junctions with barriers made of niobium silicide. Compared with the voltages produced by Josephson voltage standards based on hysteretic junctions, PJVS systems using damped junctions produce predictable voltage levels. However, in order to guarantee the quantization of the voltages and to minimize the errors at the room-temperature voltage output, additional precautions are required. We report several experimental results of voltage measurements that contain significant systematic errors. The generated voltages appear reproducible but they are, in fact, inaccurate. When proper measurement procedures are followed, the results of a direct comparison using an analogue detector show that the two independent PJVS systems agree within 2.6 parts in 1011 at 10 V with a relative total combined uncertainty of 3.4 parts in 1011 (k = 1). Investigations show that the largest systematic error and most significant contribution to the uncertainty budget is caused by the leakage resistance of each PJVS to ground. This paper describes a measurement procedure to characterize this leakage resistance and one approach to including the resulting voltage error in the uncertainty budget.

10 Volt automated direct comparison of two cryocooled programmable Josephson voltage standards

“…1. An analog nanovoltmeter (NVM), EM N11 1 , was used as a null detector to measure the voltage difference between the two cryocooled voltage standards, PJVS(1) and PJVS (2). The isolated output of the NVM was connected to a digital voltmeter (DVM) for digital readout.…”

“…Turn-key cryocooled PJVS systems are replacing conventional Josephson voltage standards, not only in national metrology institutes (NMI), but also in primary calibration laboratories (PCL). Direct PJVS to PJVS comparisons [2] are not only becoming prevalent for NMI key comparisons, but are also essential to qualify the performance of PJVS systems disseminated to the PCL. The lowest Type-A uncertainty in direct voltage standard comparisons is generally achieved with the use of an analog null detector [2,3].…”

“…Direct PJVS to PJVS comparisons [2] are not only becoming prevalent for NMI key comparisons, but are also essential to qualify the performance of PJVS systems disseminated to the PCL. The lowest Type-A uncertainty in direct voltage standard comparisons is generally achieved with the use of an analog null detector [2,3]. However, the use of an analog detector often demands fastidious manual operations to prevent any overloading during the PJVS polarity reversals required to eliminate the contributions of thermal electromotive forces (EMFs).…”

The leakage resistance to ground of a NIST Programmable Josephson Voltage Standard

“…The principle of the second experiment is equivalent to the BIPM measurement setup with the exception that the test voltage, U, is provided by a battery [3]. In this measurement configuration, the probe and array are removed from the measurement setup with the goal to evaluate the LRG contribution of the PJVS bias circuit.…”

“…PJVS systems have the potential to bring to the field of voltage metrology accuracy equivalent to CJVS, improved ease of use, and new measurement capabilities that exploit the intrinsic stability and programmability of their voltages. However, a number of precautions need to be followed in order to limit the magnitude of errors at the output of the probe [3]. The dominant precaution arises from a PJVS leakage resistance to ground (LRG) that is typically lower than that of the CJVS, which is defined as the electrical resistance of one side of the measurement leads to ground.…”