A gravity gradiometer is disclosed which has a pair of sensor bars 41, 42 mounted in housings 43 and 45. Transducers 71 are located adjacent the bars for measuring movement of the bars in response to the gravity gradient tensor. Signals from the transducers are supplied to a SQUID device 367 for processing the signals. A connector is supplied for connecting the circuitry to external equipment which comprises a container 560 having a feed through filter 564, a three terminal cap 565, a relay 566 and an output terminal. The output terminal is connected to further RF attenuation which comprises a second connector 5b having parallel inductors and resistors.