Input Impedance Calibration of Buffer-less Thermistor Temperature Measurement System
Jimin Kim, Chan-Young Park, Yu-Seop Kim, Hye-Jeong Song, Jong-Dae Kim · International Journal of Control and Automation · 2013
In this paper, a calibration method for the ADC input impedance is presented for the buffer-less thermistor temperature measurement system. In the system the thermistors are interfaced without any buffer to ADC of a temperature measurement system. While a voltage follower or a buffer is usually required to minimize the influence of the ADC input impedance, a high performance operational amplifier is required to prevent the noise and distortion due to the additional circuit. Negative power is also necessary to prevent the distortion of the low voltage input signal. A buffer-less system and a calibration method are introduced to resolve such problems. The precision resistors with low temperature coefficients were employed to emulate the thermistors in the constant temperature water bath, yielding the calibration of the input resistance and the leakage current of ADC without any usage of the inconvenient water bath. The experimental results show that the mean of the calibration error decreased from 190mK to less than 50mK. The calibration error persists in less than 50mK for 8 months long, verifying the validity of the proposed calibration method.