AN AUTOMATIC MEASUREMENT SYSTEM OF DC SQUID CHARACTERISTICS USING A COMPUTER CONTROL

We have measured DC SQUIDs characteristics using a computer controlled, automatic measurement system. This system can obtain data from four SQUIDs at a time. The following sequences of measurements were conducted: 1. The basic characteristics, current-voltage (I-V) and flux-voltage (Phi-V), were measured. 2. The noise performance was measured using the flux locked loop (FLL) mode. This system is constructed with three parts; a control computer, generally used instruments (DC source and monitor, lock-in amplifier, function generator, FFT analyzer, switch control unit), and electronics which we made, (i. e. low noise preamplifier, feedback unit). The computer drives these instruments with GP-IB interface and acquires the data. To reduce the noise, we used electrically shielded cables and magnetically shielded SQUIDs by Nb. The SQUIDs characteristics measured by this system as well as the manual measurement data, have been obtained by using the battery-operated low noise FLL electronics which we made. This system is very useful for estimating DC SQUID performance in a short time, and for developing the FLL electronics.