CALIBRATION FREE TEMPERATURE MEASUREMENT THROUGH MODEL PARAMETER EXTRACTION FROM THE P-N JUNCTION I-U CHARACTERISTIC Olfa Kanoun Institut für Meß- und Automatisierungstechnik, University of the Federal Armed Forces Munich, Germany ABSTRACT The calibration freedom contributes to a significant reduction of the costs of sensor production and maintenance. In this paper, we give a survey about the temperature measurement methods based on the p-n junction i-u characteristics and fulfilling the calibration freedom criteria. The Lack of accuracy of these methods is principally due to the deployment of simple i-u characteristic models allowing a direct calculation of temperature. Therefore, we propose to consider the inverse problem approach. Temperature would be consequently calculated through parameter extraction from an appropriate p-n junction i-u characteristics’ model. Under this new consideration, more complex i-u characteristic models could be used without affecting the conditions for a calibration free measurement. The used i-u characteristic’s model would have only to satisfy some requirements in order to improve the stability and the accuracy of the temperature extraction process. 1. INTRODUCTION The calibration is a way to examine the real behavior of a sensor specimen. It is defined as the determination of the relationship between the sensor output and the sensor input under definite operating conditions. Generally, the calibration of sensors is a process carried out during production, implementation and maintenance of sensors. Over the production process, the calibration results are considered by the design of the technology dependent sensor properties. In the final production steps, the calibration data are used for classifying the sensor specimens in classes having a specified accuracy for sale. At the implementation, sensor calibration is not always necessary. However, it could be needed to inspect the sensor functionality or to determine sensor specimens, within a sensor set, with a certain property which was not sufficiently indicated through the manufacturer. In the maintenance process, calibration serves to examine the sensor specimen on alteration caused through aging effects. The calibration data are generally used in order to determine the up-to-date sensor parameters. During the service lifetime of a sensor specimen, several calibration processes are generally carried out. Especially for frequently used sensors like temperature sensors, it is therefore important to figure out the calibration costs in order to calculate the global charges related to calibration. In this paper we especially consider temperature sensors for the military temperature range between 218.15 and 398.15 K. 2. CALIBRATION OF TEMPERATURE SENSORS In a study about calibration costs of resistance thermometers we considered most of the accredited calibration laboratories in Germany. The experience made thereby shows difficulties for the customer to determine the laboratory with the most favorable costs for a certain calibration procedure. This is due to the difference in the formulation of quotations. Generally, the calibration costs can be divided in fixed and variable costs depending on the number of sensors n and on the number of calibration points p. ∑ ∑ = = + = p 1 j 2 n 1 i 1 ) n , j ( R sts VariableCo ) i ( R FixedCosts nCosts Calibratio (1) Where n is the number of the calibrated sensors p is the number of calibration temperatures R 1 is the costs reduction related to the number of sensors and R 2 is the costs reduction related to the number of calibration temperatures and possibly also related to the number of sensors.