Errors caused by temperature differences - HM70

HM70 User Guide

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In humidity measurement and especially in calibration, it is essential that the temperature of the probe and the measurement environment are the same. Even a small temperature difference between the environment and the probe causes an error. As the curve in the following figure shows, if the temperature is +20 °C and relative humidity is 100 %RH, a difference of ±1 °C between the environment and the probe causes an error of ±6 %RH. When the humidity is 90 %RH, the corresponding error is ±5.4 %RH.

A temperature difference of a few degrees can also cause water to condense on the sensor surface. The HUMICAP® sensor starts to function normally as soon as the water has evaporated. If the condensed water is contaminated, the life span of the probe may shorten and calibration may change.

Figure 1. Measurement error at 100 %RH with 1 °C difference between the ambient and sensor temperature