TH02

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2.4. Temperature Compensation

The TH02 relative humidity sensor is calibrated at a temperature of 30 °C; it is at this temperature that the sensor

will give the most accurate relative humidity readings. For relative humidity measurements at other temperatures,

the RH reading from the TH02 must be compensated for the change in temperature relative to 30 °C.

Temperature compensated relative humidity readings can be calculated as follows:

Where:

Temperature is the ambient temperature in °C as measured by the TH02 on chip temperature sensor.

This temperature compensation is most accurate in the range of 15–50 °C. The values for the correction

coefficients are shown in Table 9.

Table 9. Linearization Coefficients

Coefficient

Value

0.1973

0.00237

2.5. Hysteresis

The moisture absorbent film (polymeric dielectric) of the humidity sensor will carry a memory of its exposure

history, particularly its recent or extreme exposure history. A sensor exposed to relatively low humidity will carry a

negative offset relative to the factory calibration, and a sensor exposed to relatively high humidity will carry a

positive offset relative to the factory calibration. This factor causes a hysteresis effect illustrated by the top and

bottom (blue) traces in Figure 7. The hysteresis value is the difference in %RH between the maximum absolute

error on the decreasing humidity ramp and the maximum absolute error on the increasing humidity ramp at a single

relative humidity Setpoint and is expressed as a bipolar quantity relative to the average, the center (red) trace in

Figure 7. In the case of Figure 7, the measurement uncertainty due to the hysteresis effect is ±1.05%RH.

2.6. Prolonged Exposure to High Humidity

Prolonged exposure to high humidity will result in a gradual upward drift of the RH reading. The shift in sensor

reading resulting from this drift will generally disappear slowly under normal ambient conditions. The amount of

shift is proportional to the magnitude of relative humidity and the length of exposure. In the case of lengthy

exposure to high humidity, some of the resulting shift may persist indefinitely under typical conditions. It is generally

possible to substantially reverse this affect by baking the device.