The design, development and testing of a precision temperature monitoring system

The purpose of this project was to develop an accurate and reliable system which can monitor multiple temperature points located in widely separated locations in a cost effective manner.

In the system that was designed and constructed, each unit consisted of fifteen thermistor-type temperature probes which were interfaced to a commercially available single-board computer. Design modifications were instigated for the single-board computer to increase its resolution and a program that implements the nonlinear relationship between resistance and temperature in thermistors was developed. The calculated temperatures were transmitted over a serial communications link to a customized data logger where they were averaged over various times and stored. A central minicomputer called several of these temperature units over standard phone lines and collected the averaged data.

This thesis describes the work related to the theoretical considerations involved in the use of thermistors as temperature sensors, the design of the thermistor drive circuit, the modifications to the single-board computer's analog section, and the software that was written for the precision temperature microcomputer.

The resulting system design exceeded all initial design specifications for accuracy, resolution and scan speed. A complete network of four temperature systems was constructed and installed at the Vermont Yankee nuclear power plant in September, 1984. Since then, all of the units have been functioning normally.