Pulse Train Modulation And ANN Based Temperature Sensor With Semi-automatic Calibration

The paper presents a temperature measurement system involving thermocouples. An NTC thermistor, as an inexpensive electronic component, plays dual role in the experimental setup. Firstly, it keeps track of temperature at cold junction of the thermocouple. Secondly, it modulates the ON and OFF time of pulses generated from a 555 timer based astable multivibrator. The thermocouple signal feeds the control input of the 555 timer. The multivibrator output is fed to a pre-trained ANN embedded in a personal computer (PC), to complete the measurement. The scheme has an arrangement for calibration involving a multitude of knots, resulting in very effective training of ANN. The semiautomatic calibration arrangement facilitates ANN to be trained with more data. The system is capable of measuring any unknown temperature, irrespective of the cold junction temperature. The experimental validation of the proposed scheme employs a type-T thermocouple. A measurement error of approximately $\pm 0.38^{\circ}{\mathrm C}$ is obtained over temperature range from $55^{\circ}{\mathrm C}$ to $138^{\circ}{\mathrm C}$. The proposed measurement system outperforms all the thermocouple-based temperature measurement techniques proposed in recent literature, in terms of accuracy, reliability, cost, and potential for embedded system application.