Modification of a Hughes tiltmeter to a borehole tiltmeter

Earth tidal tilt measurements in mines are influenced by cavity effects. Therefore, the modification of tiltmeters to borehole instruments is useful, since the cavity effect may be avoided in boreholes. The principle of the design of the Hughes tiltmeter and of borehole equipment is described. The diameter of the borehole case is similar to that of the Askania vertical pendulum. Hence the Hughes tiltmeter can be installed in boreholes drilled for Askania pendulums. To achieve proper operation of the instrument, the electronics had to be reconstructed and integrated in the borehole case. Devices for remote adjustment of the tiltmeter in the borehole, self test, temperature, and air pressure sensors complete the borehole equipment. The borehole tiltmeter is connected via a 60 m long cable with the control unit, containing the necessary power supplies, analog control instruments and adjustment knobs.