Temperature compensation is a functionality introduced in software version 1.1.0. The HMP7 probe supports probe heating. Probe heating heats up not only the sensor, but the entire probe head and filter. When probe temperature is heated above dew point temperature, condensation on the probe can be avoided while measuring the dew point temperature of the process. The probe heating functionality in HMP7 can be activated either through configuration code (set at the factory), or it can be activated using the Insight software and service cable (Vaisala part number 242659 or USB-2).
Output parameters that are dependent on temperature measurement (such as relative humidity) are unavailable whenever probe is heated unless the true temperature of the measured environment is updated to the temperature compensation register of the HMP7 from the TMP1 probe. This happens automatically when both HMP7 and TMP1 are connected to the transmitter and the temperature compensation function is enabled. If TMP1 is disconnected and temperature compensation is not manually turned off, a NaN value is returned. Disconnecting TMP1 will invalidate the temperature and relative humidity outputs of the heated HMP7.
Temperature compensation setting is usable only when HMP7 is connected to probe 1 connection terminal and TMP1 is connected to probe 2 connection terminal. It does not affect any other probe combinations. When the probes are connected, the temperature compensation automatically turns on. The temperature output of HMP7 is equal to TMP1 temperature, when heating function is activated. Make sure HMP7 and TMP1 probes are in the same environment to get the most accurate relative humidity measurement values.
The compensation can be manually turned off.