USA interlaboratory comparison of superconductor simulator critical current measurements

An interlaboratory comparison of critical current (I/sub c/) measurements was conducted on the superconductor simulator, which is an electronic circuit that emulates the extremely nonlinear voltage-current characteristic of a superconductor. These simulators are high precision instruments, and are useful for establishing the integrity of part of a superconductor measurement system. This study includes measurements from participating US laboratories, with NIST as the central, organizing laboratory. This effort was designed to determine the sources of uncertainty in I/sub c/ measurements due to uncertainties in the measurement apparatus, technique, or the analysis system. The participating laboratories measured the superconductor simulator with a variety of methods including DC and pulse. This comparison indicated the presence of systematic biases and higher variability at low voltages in the I/sub c/ determinations of the measurement systems. All critical current measurements at a criterion of 10 /spl mu/V on the I/sub c/ simulator were within 2% of the NIST value for nominal critical currents of 2 and 50 A. These results could significantly benefit superconductor measurement applications that require high-precision quality assurance.<>