My temperature sensor is reading high. Why is this?

To get meaningful temperature measurements, the temp-sensor/measurement system must be accurate, the temperature sensor must be located where the temperature needs to be measured, and the temperature sensor must be mounted or attached in such a way as to minimize stray thermal conduction. Temperature sensors have a finite thermal mass, and must be connected to a measurement circuit in a way that permits some thermal conduction between the circuit and the sensor. In addition, most sensors have self-heating which is the heating of the sensor due to the electrical power that the sensor itself dissipates. The temperature rise seen on the RSMini is not due to self-heating, it is due to thermal conduction from the Web server. The effect of thermal mass is to delay the response of the sensor to a change in temperature and to filter out any rapid changes in temperature. This is often specified as a thermal time constant which is a measure of the time it takes the sensor to respond fully to a step change in the temperature (approximately a minute or more). Attaching the sensor to a circuit board or cable will increase the thermal time constant. The thermal time constant is also a function of the humidity and air speed. Secondly, the method of attaching the sensor can be critical. If it is attached to a surface or object, the temperature measurements may be more related to the temperature of the surface or object than the surrounding air. In addition, hot spots (and occasionally cold spots) can develop, especially inside cabinets. It is best to mount the sensor by clamping the cable some distance from the sensor and using the stiffness of the wire cable to hold the sensor in place. Hanging the sensor has the same effect. Unless the customer specifically wants to measure for hot spots the sensor should be placed in moving air, preferably air that is being forced to move with a fan. Ensuring good air flow across the front of the unit will improve the quality of the internal temperature measurement.