Micro-PCR Chip NTC-Thermistor Sensor-Calibration System

In this paper, we implement a Steinhart-Hart calibration-factor value measurement system to obtain accurate temperature measurements of a negative-temperature coefficient thermistor. The thermistor is mounted on a micro-polymerase chain reaction (PCR) chip in a micro-PCR systemthat requires accurate temperature measurement and control. When obtaining the calibration-factor value, it is impossible to accurately measure and control the temperature unless the measured resistance error is set to 1%. Considering this characteristic, we use the sensor of a to-be-calibrated chip to obtain accurate temperature control of a pre-calibrated chip, and we simultaneously measure the resistance value that corresponds to the temperature of the heating pattern of the precalibrated chip.After attaching a thermal pad on the heating pattern of the pre-calibrated micro-PCR chip for heat transfer, we press it as close as possible against the thermal pad on the heating pattern of the to-be-calibrated chip. When the temperature goal is reached in each of the four sections, we measure the resistance value of the to-be-calibrated chip sensor several times in order to obtain their average values. The results obtained show that the temperature error rate was within the tolerance range when the sensor of the tobe-calibrated chip measured the temperature of the heating pattern in the pre-calibrated chip. We obtained three calibration factor values from the four average resistance values. We record the calibration factor values using an electrically erasable programmable read-only memory attached on the chip, and we perform temperature calibration by again reading the calibrated values from the chip. A conventional calibration system using a constant-temperature water tank takes a long time to reach each target temperature section. However, the calibration system proposed in this paper requires a short time to reach each target temperature, and we therefore confirm that the calibration task time is less than that of conventional calibration systems.