Condensation prevention functions - HMP1 - HMP3 - HMP4 - HMP5 - HMP7 - HMP8 - HMP9 - HMPX - MMP8 - TMP1

HMP Series with MMP8 and TMP1 User Guide

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Condensation prevention functions prevent water from condensing on the sensor and interfering with humidity measurement. Use of condensation prevention is controlled by a single setting that can be changed with the Insight software, the Indigo80 handheld indicator, or using the Modbus protocol. The setting is only available if your probe supports condensation prevention.

By default, condensation prevention is off.

However, the HMP7 model can be ordered from Vaisala with the feature enabled.

When condensation prevention is enabled, the probe will automatically use its available condensation prevention functions. When warming is active, values of output parameters that depend on temperature measurement (for example, relative humidity) are unavailable, unless the temperature compensation setting is set to read the temperature from an external source. Output parameters that can be measured or calculated without this external temperature information, such as dew point temperature, are available even without the temperature input.

Sensor warming

Sensor warming is available to all HMP series probes with composite sensors, HMP1, and HMP9.

Sensor warming warms the humidity sensor when necessary to keep its temperature above the dew point of the measurement environment. When sensor warming is activated, all temperature-dependent output parameters become unavailable, unless the temperature compensation setting is set to read the temperature from an external source. The output parameters become available again 4 minutes after the warming is stopped.

Sensor warming is intended for improving the condensation tolerance of the probe in measurement environments that may occasionally cause condensation to form. It is not intended for environments where continuous warming is needed.

Probe heating

Probe heating is available on HMP7 model only. Probe heating warms up the entire probe head instead of just the sensor. It is intended for use in challenging measurement environments where condensation on the probe would otherwise present a problem.

Probe heating always applies some heating power even when the sensor is not near condensation, so temperature-dependent output parameters are permanently unavailable when probe heating is used, unless external temperature information is provided to the probe.

If the ambient dew point rises close to current sensor temperature, the heating power is increased to avoid condensation.

If you use probe heating, be sure to mount the HMP7 probe head in a way that prevents the heat from being conducted away from the probe. Tightly connecting the HMP7 probe head to a metal structure may prevent the probe from maintaining probe temperature above the dew point. It will also heat the structure which may be undesirable.
Even if condensation prevention has been turned on, probe heating is not active if supply voltage is below 18 V DC. For example, this is the case when HMP7 probe is connected to Insight software using the Indigo USB Adapter.