THEORETICAL ANALYSIS OF THERMISTOR TRIMMING

The application of thick film thermistors has been increased during the last decade. In order to achieve high sensing accuracy the thermistors should be trimmed. The error sources were thoroughly analyzed: the effects of the inaccuracies of the ambient tem-perature, the temperature measurement, the heat transients caused by the laser pulses, and the resistance measurement were discovered and examined. It was pointed out that the specific requirements can be fulfilled only by keeping the thermistor on its working temperature during trimming. If an on-line correction according to the in-situ measured temperature of the thermistor under trimming is applied, even the error caused by the ambient temperature can be eliminated. The requirements of a laser system suitable for thermistor trimming have also been outlined.