Many known measuring devices do not perform as they should under an external influence. In particular, measuring devices do not perform correctly when temperature is the external influence. This occurs because many measuring devices, or the actual measuring section of such measuring devices, supply output values that are no longer in the necessary proportion to a measured quantity on the input side when the temperature changes. For example, semiconductor-based pressure sensors used in the form of pressure or differential-pressure transducers in measuring devices are frequently so highly dependent on temperature that they no longer satisfy the required measuring accuracy. The specified measuring accuracy can be achieved only by compensating for the temperature-caused errors. Such compensation can be carried out especially well in measuring devices having a programming section. This can be done because, in combination with a data processing system, the programming section can be used to set the relevant measuring device so that its output value remains almost unaffected by changes in temperature. In the case of pressure or differential-pressure transducers, these devices are known as intelligent sensors. The intelligent sensors include the sensor and an associated programming section.
A process is described in a publication "Piezoresistive und kapazitive Drucksensoren mit integrierter Signalvorverarbeitung" (Piezoresistive and Capacitive Pressure Sensors with Integrated Signal Preprocessing), joint project 1989 to 1992, Final Report Technische Universitat Berlin, Fraunhofer-Institut fur Mikroelektronische Schaltungen und Systeme, Duisberg, and University of Stuttgart, Vol. 9, 1994, pp. 19-20. In this conventional process, pressure sensors having thermal characteristics which are to be compensated for are placed in a temperature test cabinet which is heated in stages for the purpose of compensation. Each time the cabinet is heated to the next higher temperature, implementation of the conventional compensation process is delayed for a certain period of time to ensure that the pressure sensors to be compensated for have indeed reached the temperature set in each case in the cabinet. Once this temperature has been reached, a measurand is supplied from the pressure sensor to a data processing system via a multiplexer. Once the relevant temperature values and the output values of the pressure sensors have been entered in this manner in the data processing system at the predetermined temperature levels, the data processing system generates signals compensating for the temperature dependence and provides them to the programming section of the pressure sensors, thereby ensuring that the output values provided by the pressure sensors are proportional to the measured quantities on the input side regardless of the changes in temperature.
The conventional process for compensating for the incorrect operation of measuring devices (fitted with a programming section) caused by changes in temperature is very time-consuming because detection of the measurand must be delayed for a relatively long period each time the temperature is increased in the chamber of the temperature testing cabinet until the measurement devices to be tested have reached the temperature of the chamber. This considerably increases the production time for the measuring devices or pressure sensors, which makes the manufacture of pressure sensor relatively expensive.
U.S. Pat. No. 5,319,965 describes a pressure recording device in which pressure measurement results unaffected by changes in temperature are obtained by taking into account calibration values stored in a memory. However, this patent does not describe how these calibration values are obtained.
Moreover, a method in which a range of temperatures is traversed without stopping to automatically detect the dependence of measured quantities on temperature is described in German Patent Application No. 33 40 207. Measuring signals corresponding to the measured quantity dependent on temperature are detected with a temperature sensor at predetermined temperatures. An error function that is available for the temperature compensation of measuring signals obtained individually is formed from corresponding value pairs, and another temperature sensor is required to carry out the actual temperature compensation.
A differential-pressure transducer in which a temperature sensor is integrated into the transducer is also described in "IECON '84", Proceedings of 1984 International Conference on Industrial Electronics, Control and Instrumentation, Tokyo, Japan, Vol. 2, Oct. 22-26, 1984, pp. 1081-86. The temperature sensor is used to obtain and take into account correcting quantities to account for the temperature dependence of the output value of the differential-pressure sensor belonging to this transducer. The publication does not describe a specific way in which this is accomplished.
A method for detecting and recording the performance of a pressure sensor depending on changes in temperature is also described in U.S. Pat. No. 4,845,649. This patent does not describe the specifics of how this is accomplished.
European Patent Application No. 0 580 462 describes a process that is largely identical to the process explained in detail above.