This paper critically discusses the performance of an NTC thermistor sensor in the temperature range 20 o C to 85 o C and provides a technique for linearization of the temperature sensed by the thermistor. The linearization was achieved by utilizing Wheatstone bridge electronic circuitry which responds to the thermistor and produces an output which is an exponential function of the temperature sensed by the thermistor sensor. A further simple and low-cost electronic circuitry responds to such output and converts the resistance measurement to provide a signal which represents the temperature. Moreover, the Wheatstone bridge signal conditioning circuitry was designed to have 0 -100 mV output voltage within the considered temperature range. The physical characteristics of the thermistor (constant A and b) were found to be 4.0015 x 10 -5 ± 0.2956 x 10 -5 Ω and 3514.8 ± 11.6 K respectively. The result also shows that the percentage nonlinearity was as low as 1.7 and a sensitivity value of 1.5661 mV/K was found for the thermistor, but the resolution of this thermistor sensor is 2 o C. However, the percentage of nonlinearity obtained was in agreement with the theoretical percentage nonlinearity.
In this paper, we report the design of a signal conditioning and acquisition elements of a chopped broadband radiation pyrometer for measuring temperature in the range of 900 0 C to 1200 0 C. We also report the selection of a suitable chopping frequency within the physical properties of the system and provided the calibration characteristics for the pyrometer. Based on the results, it was found that the designed signal conditioning circuit was able to produce an output voltage of 0.24 -0.60 V corresponding to the temperature measuring range of the pyrometer. This was achieved through the use of a phase-sensitive detector (PSD) in the form of a lock-in amplifier in combination with a low pass filter. A suitable chopping frequency of 30 Hz was chosen for the shutter pulse so that the detector can have sufficient time to settle before the next shutter pulse transition. Finally, the result also shows that the calibration characteristic of the pyrometer presumes an approximately linear relationship.
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