Calibration of Downhole Temperature and Pressure Instruments

Abstract

The Ministry of Works Geothermal Projects operates a high-temperature circulating oil bath at Wairakei which is used for calibration of "Kuster" downhole recording temperature gauges. A platinum resistance thermometer attached firmly to the gauge is used to measure its temperature and provide control information. Downhole pressure gauges are also immersed in the bath as part of their calibration procedure, since their response is ent to a small extent (up to 1% of full scale). Careful choice of temperatures is necessary to achieve the nominal gauge accuracy in minimum calibration time. Bath temperatures can be held within indefinitely over a range from ambient to Thermal lag of the gauge reduces this variation to about indicated.