Design of resistive temperature compensation by single and multiple thermistor networks

An accurate and practical solution to the design of linear negative temperature coefficient resistive networks, which will improve system performance over defined temperature ranges, is described herein. The basic circuit is a nonlinear negative temperature coefficient semiconductor, generically known as a thermistor, in parallel with a shunt. The temperature range of utilization of the basic circuit is about 60 C (degrees centigrade). Two or more of these basic circuits are connected in series to provide nearly linear characteristics over an extended temperature range. Graphical presentations of the basic circuit characteristics are used in an original manner, the graphs being easier to use and more complete than those previously published. Proper selection by a graphical method of the basic circuits connected in series, for wider temperature range use, is explained, and an analytic discussion tells how the graphs are constructed. The errors caused by circuit tolerances and self-heating, and the selection of thermistor materials, sizes, and shapes are outlined. Typical examples illustrate the use of the graphs and techniques. Application of the networks to temperature compensation and temperature measurement, as well as extension of the techniques to nonlinear applications, receive careful thought.