A modified linearized thermistor thermometer using an analog multiplier

A scheme to measure temperature using a thermistor probe has been suggested by A.A. Khan et al. (see ibid., vol.37, p.322-232, June 1988). In this circuit, Khan et al. have used an analog multiplier in the divide mode to eliminate the need to know the actual value of the thermistor constant, beta . This scheme also provides a wide linear range, as is shown by their experimental results. However, two problems are noted in the circuit. This scheme requires the generation of a reference voltage E/2 and the use of a difference amplifier. A difference amplifier requires tightly matched resistors so that the common mode gain can be made as small as possible. A modification to this circuit is suggested in which these two problems can be eliminated. It is also found that only one adjustment is needed for calibration in the modified scheme. >