The calibration of a portable induction magnetometer system

An investigation made concerning the characteristics of a sensor coil for an induction magnetometer shows that it is feasible to make the first stage 60 Hertz rejection filter of the Butterworth type. This is an improvement in design over the Twin-T filter which is sometimes used as a first stage filter as the number of electrical components is reduced and there is no possibility of ringing between the coil inductor and the filter capacitors. Two methods of relative calibration for the induction magnetometer system give reliable response curves. One method uses a Wheatstone bridge. The sensor is one arm of the bridge and it is shown that the effect of the signal generator is the same as if the coil was excited by a natural event. The second method involves exciting the sensor by a field created by a small secondary coil. The agreement between the two methods is good. An experimental approach to the absolute calibration is successfully carried out by comparing the output from the uncalibrated system to an air core system which has been previously calibrated. A theoretical approach is used to give a good indication of the sensitivity of the sensor coil. The sensitivity is dependent primarily upon the turn number and the length of the coil.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat