Calibration of an ingestible temperature sensor

An ingestible telemetric sensor for measuring core body temperature is increasingly being utilized in occupational and athletic studies of heat strain. There is a need for a uniform method of calibrating these sensors in the scientific community in order to effectively compare the results of different researchers. The purpose of the present investigation was to determine and present such a calibration procedure. Sensors were placed in a water bath heated to nine discrete temperatures, and the recorded values were compared to that of a traceable thermometer. It was observed that sensor 2 recorded temperatures higher than sensors 1 and 3, and that all sensors were higher than the traceable thermometer, highlighting the need for a calibration procedure. The findings of this study suggest a number of recommendations for a calibration procedure including: (1) four water bath temperatures in the range of 33-41 degrees C should be utilized; (2) sensors should be immersed for a minimum of 4 min prior to taking a measurement; (3) a linear regression relating sensor temperature to a traceable thermometer is an appropriate method to adjust raw data. Switching the sensor off after calibration and reactivating it prior to ingestion will not influence the accuracy of temperature measurement.