Calibration and polarity of SIROTEM down-hole probes

Abstract Procedures have been developed for the calibration of a SIROTEM down-hole probe, and for determining the correct polarity of connections to the probe in the field. An exponentially decaying signal derived from the calibration unit and driven into the transmitter loop in the same direction as required for field operations induces a similar signal in the probe placed inside this loop. By connecting the probe so as to obtain a positive response, the correct polarity of the connections to the probe is ensured before the beginning of a down-hole survey. Such a check may be applied equally well to any sensor other than a down-hole probe, e.g. to check the polarity of the connections to a roving vector receiver. The frequency and phase response of the slimline down-hole probe has also been measured. The band-width is ∼20 kHz.