MICROCOMPUTER BASED TEMPERATURE MEASUREMENT

Abstract

In this dissertation, the work has been carried out 'on improving the techniques for accuarate temperature measurement. In first part of the work, three techniques have been developed for the accurate temperature measurement using thermistor, ' thermocouple and PRT. 'sensors. These techniques are combination of hardware and software. With the changed sensor, modifications have - to be carried out in the signal processing components of each circuit. Signal conditioning circuits, which convert the sensor output ' into a voltage signal, have been designed, fabricated -and tested for each sensor. These circuits are designed considering the transfer -characteristics of each sensor. The bridge circuit designed for thermistor compensates partially. for the non- linearity of its characteristics. The design of an` automatic reference junction circuit for, a thermocouple have been taken up in this work. An' approximatly -linear bridge has been: designed for PTR sensor. The output of each processing 'circuit is converted to digital signal by an AID. converter and then further processed in-the computer by using the mathematical relationships to get . accurate temperature measurement. In case of' thermocouple, the computer solves a quartic equation to arrive at an improved -estimate of temperature.' A quadratic equation is solved to find.; temperature in , case of PRT sensor. Liriearisation of thermistor characteristic is very essential for 'measurement and control of temperature in many industrial processes. Software technique is used for linearizing the highly non-linear characteristic ' of thermistors for accurate. temperature measurement. In second part of the . work, the_ non linear characteristic of. 4. NTC thermistor has been linearised using an iterative algorithm. The method has a low storage requirement and is capable of on-line operation. It has flexiblity of incorporating the changes of - device specifications in the software itself. All three techniques developed in first part of the work and ' linearization technique developed in . second part of .the work have been tested successfully. The experimental 'results are consistent and conformed to expected performance stipulated at the design stage. iv