Apparatus for detecting a fine magnetic field with characteristic testing function of a DC squid

摘要

An apparatus for detecting a fine magnetic field comprises a DC SQUID which detects and converts a magnetic field to an electrical signal. A flux locked looped circuit drives the DC SQUID. The flux locked loop circuit includes an amplifier for amplifying the electrical signal. A phase detector modulates the amplified electrical signal and an integration circuit outputs a voltage signal corresponding to the detected magnetic field. An oscillator coupled to the phase detector supplies a demodulation frequency signal. A modulator including a first voltage-to-current converter and a second voltage-to-current converter is coupled with the integration circuit and the oscillator for supplying a modulation signal to the DC SQUID. The modulator further includes an external input terminal and a feedback modulation change-over circuit for changing an internal feedback signal to an external test signal inputted to the external input terminal. A bias source having a third voltage-to- current converter is coupled to the DC SQUID and supplies a bias signal. The bias source also includes an external input terminal and a change- over circuit for changing an internal bias signal to an external test signal inputted to the second external input terminal. An external output terminal is connected to the amplifier for supplying a monitoring test output signal from the DC SQUID. The apparatus for detecting a fine magnetic field thus provides a self-testing function for the DC SQUID.