3.3 Condensation prevention functions
Condensation prevention heating prevents 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 Insight software or using Modbus protocol. The setting
is only available if your probe supports condensation prevention.
By default, condensation prevention is o. 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
temperature is written to register 0334
hex
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.
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 external temperature information is provided to
the probe. 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 continous 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. Heating power also increases as supply voltage increases.
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.
HMP Series with MMP8 and TMP1 User Guide M212022EN-F
18
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