Applications of transient response characterization and enhancement to thermal instrumentation

Thermal sensors have transient response characteristics that may be examined using external or internal stimulation tests. The test data can be coupled with simple sensor models, consisting of two or three term approximations to the solution of partial differential equations, or more complex ones based on techniques such as the unsteady surface element method. The test data provides information for determining the unknown parameters in the approximating equations. The combination of model and test data is used to produce an estimate of the transfer function represented by the sensor. The estimate can then be applied to experimental data obtained from the sensor to improve the quality of the information. The technique of combining step response data and simple models has been applied in a variety of cases. Some of the applications include the effects of adhesive on the response of surface mounted resistance temperature detectors, the use of an on-line circuit in a flight vehicle to monitor the bonding condition of mounted sensors, a project aimed at improving the resolution of temperature data obtained from the containment building of the TMI-2 nuclear power station and for compensating the output from an intrinsic thermocouple. Response compensation requires a model that represents the inverse of the transfer function of the sensor. The previously mentioned experiments have shown that simple models can provide adequate representations of sensor for the purposes of compensation. A thermal sensor acts as a low pass filter which attenuates information necessary for determining the parameters of response models. In combinations with system noise, the filtering effect limits the accuracy of any compensation system such that simple models will provide results commensurate with more detailed ones