| Superconducting quantum interference devices have been used as the key sensors in precision gravity instruments. Its property parameters have significant influence on the ultimate performance of the gravity instruments. To understand to what degree the SQUI-D sensor will constrain the performance of gravity instruments, systematic measurements have been taken for the SQ2600-type SQUID.Firstly, the SQUID noise has been measured within 500Hz frequency range, under varied experimental conditions. The results show the noise level can change from 6??0/ (?)Hz to 10??0/(?)Hz, depending on the level of electromagnetic interference. The best me-asured result is in the well shielded vaccum chamber, closest to claimed value. By comp-aring the SQUID noise level under several designed experimental environments, helpful suggestions have been given to shield SQUID to approach its fundamental noise level.Secondly, the frequency response of SQ2600-type SQUID, including the amplitud-e-frequency and the phase-frequency characteristics, have been measured within the freq-uency range from OHz to 51.2kHz. The following conclusions can be drawn from the me-asurements:(1)the bandwidth of SQ2600 is above 10kHz, (2)the gain and phase of SQ2600 increase gradually within 51.2kHz.Thirdly, by measuring the transfer function of the SQUID with different inductan-ce loads in current-lock feedback mode, the expression of SQUID sensitivity with respect to loads has been precisely determined. This results is of key importance when the SQUI-D is used to construct feedback control system for gravity instruments. |
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