Response of installed temperature sensors

Two new methods have been developed to permit evaluation of the time response of installed temperature sensors. One permits improved a priori estimation of the response that will be obtained upon installation and the other permits in situ evaluation of the response of the sensor after installation. The a priori method requires response measurements at two or more fluid flow conditions to evaluate an internal (or intrinsic) component of the time constant that is independent of fluid conditions and a surface component that depends on fluid conditions. Estimation of the sensor response in other fluids is obtained from the heat transfer correlations for other fluids. The in situ method provides the time response of installed thermocouples and resistance thermometers by passing an electric current through it and measuring the transient response of the sensor following cessation or initiation of the Joule heating. This response can be analyzed to predict the sensor's response to a fluid temperature change. This measurement permits the response time qualification of newly installed sensors and subsequent monitoring of changes in response time with service.