A Thermometer Based on Diverse Types Thermocouples and Resistance Temperature Detectors

A universal and low-cost temperature thermometer is realized via a special circuit,integrated circuit chip with microprocessor and analog to digital converter,and digital bus interface.Various thermocouples and resistance temperature detectors used for temperature sensing may be connected to same thermometer.A special signal condition circuitry is designed and a matching algorithm is proposed.A novel calibration method named disassembled calibration is proposed in order to enhance efficiency and flexibility for the whole system.Additionally,it presents a combination method of low order polynomial fitting and piecewise linearity for the nonlinearity calibration of the thermocouple and the resistance temperature detector.A cold junction compensation based on digital way is described.And the matching algorithm and calibration method may eliminate errors stemming from excitation voltage source and reference voltage source,and can weaken quantization error of analog to digital converter and drift of components,too.Furthermore,the 400 times oversampling is completed by sequential and equal interval sampling to upgrade accuracy of analog to digital converter from original 12 to 15 bits and to raise signal-to-noise ratio.Finally,during a long time monitoring,experiment results show that errors at each static point are less than±0.2°C for the thermocouple system and less than±0.1°C for the resistance temperature detector system.

A universal and low-cost temperature thermometer is realized via a special circuit, integrated circuit chip with microprocessor and analog to digital converter, and digital bus interface. Various thermocouples and resistance temperature detectors used for temperature sensing may be connected to same thermometer. A special signal condition circuitry is designed and a matching algorithm is proposed. A novel calibration method named disassembled calibration is proposed in order to enhance efficiency and flexibility for the whole system. Addition- ally, it presents a combination method of low order polynomial fitting and piecewise linearity for the nonlinearity calibration of the thermocouple and the resistance temperature detector. A cold junction compensation based on digital way is described. And the matching algorithm and calibration method may eliminate errors stemming from excitation voltage source and reference voltage source, and can weaken quantization error of analog to digital converter and drift of components, too. Furthermore, the 400 times oversampling is completed by sequential and equal interval sampling to upgrade accuracy of analog to digital converter from original 12 to 15 bits and to raise signal-to-noise ratio. Finally, during a long time monitoring, experiment results show that errors at each static point are less than ±0.2 ℃ for the thermocouple system and less than ±0.1℃ for the resistance temperature detector system.