A thermistor nomograph for a three-point fit

A description is given of a nomograph which has been designed to determine all thermistor three-point fit curves that are `parallel' to a desired curve. The nomograph first establishes the resistance to the minimum thermistor and the associated minimum network. If the parallel curve for this network is less than the desired curve, it can be realized. A higher resistance thermistor increases the parallel curve. Any such curve that is lower than the desired curve can be used. The difference in resistance is removed with a build-out resistor. The nomograph is designed for temperatures of 4°C (40°F), 32°C (90°F), and 60°C (140°F). These are equal intervals above and below 32°C. 32°C is somewhat higher than the usual room temperatures to allow for the presence of internal heating of the cabinet. The design is based on negligible self-heating of the thermistor.