The surface sensor is only able to measure its own temperature and an attempt must be made to make the surface and sensor temperatures the same. This can be done by placing insulation over the sensor to reduce the effects of the environment and by choosing a mounting method that provides good thermal contact between surface and sensor.
The method chosen for mounting the sensor is equally important, while good thermal contact is desired, a large mismatch in thermal expansion coefficients may cause strain in a wire Resistance Temperature Detector sensor. This strain will produce a change in resistance that could be misinterpreted as a temperature change. Most RdF flexible models use miniature supported thin film sensing elements which eliminate strain effects in surface mounted RTDs.
When mounting both resistance and thermocouple sensors the leads should be in contact with the sensing surface for some length to reduce the effects of thermal conduction from the sens-ing wire or junction.
As can be seen by this introduction, an accurate surface temperature measurement is not a simple matter. A review of the app-lication and a procedure for installation should be considered prior to ordering. It is our intention in these application notes to provide general guide lines for the use of surface sensors.