An automatic measurement system of DC SQUID characteristics using a computer control

The authors have measured the characteristics of DC superconducting quantum interference devices (SQUIDs) using a computer-controlled, automatic measurement system. The system can obtain data from four SQUIDs at a time. The following sequences of measurements were conducted: (1) the basic characteristics, current-voltage and flux-voltage, were measured and (2) the noise performance was measured using the flux locked loop (FLL) mode. This system is composed of three parts: a control computer, commonly used instruments (DC source and monitor, lock-in amplifier, function generator, fast-Fourier-transform analyzer, and switch control unit), and electronics, (i.e. low-noise preamplifier and feedback unit). The computer drives these instruments with a GP-IB interface and acquires the data. The SQUID characteristics measured by this system as well as manual measurement data have been obtained by using battery-operated low-noise FLL electronics. This system is very useful for estimating DC SQUID performance in a short period of time, and for developing FLL electronics.<>