2 Temperature Accuracy Compensation

In thermostat and temperature/humidity controllers where a temperature differential exists between the inside and the outside of the case, the sensor will return values consistent with the air temperature and moisture inside the case, rather than the external values. To compensate for this difference, the designer must characterize the entire system for temperature output vs ambient temperature. Figure 2-1 shows an example of a relationship between the ambient temperature and the sensor error from -40 °C to 125 °C. Systems should be characterized across the complete range required by their application requirements.

Figure 2-1 System Temperature Error Across Ambient Temperature

In this graph, the effects of the temperature differential are more pronounced at lower temperatures than at higher temperatures. This may or may not be the case in the characterized system, but the temperature compensation methodology is the same regardless. Depending on the distribution the designer should compensate the sensor temperature using either:

• A linear/polynomial regression
• A lookup table