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6.2.3 Measurement of relative humidity using the combined humidity/temperature probe
The instrument works by using combined humidity/temperature probes (temperature with Pt100
sensor). The combined humidity/temperature probes are fitted with SICRAM module that acts as an
interface between the sensor on the probe and the instrument. There is a microprocessor circuit with
a permanent memory inside the module that enables the instrument to recognize the type of probe
connected and to read its calibration information.
The probes are detected during turn on, and this cannot be performed when the instrument is
already on, therefore if a probe is connected and the instrument is on, it is necessary to turn it
off and on .
Measurement of relative humidity
The humidity probes are humidity/temperature combined probes: The humidity sensor is a
capacitive type sensor, the temperature sensor is a Pt100 (100Ω at 0°C).
The instrument measures relative humidity %RH and temperature, and starting from the fixed
barometric pressure value of 1013.25mbar it calculates the following resulting quantities:
•
g/kg
Grams of vapor in a kilogram of dry air
• g/m
3
Grams of vapor in a cubic meter of dry air
• hPa
Partial vapor pressure (hPa)
• J/g
Enthalpy
• Td
Dew point (°C or °F)
• Tw
Wet bulb temperature (°C or °F)
A measurement is performed by placing the probe in the area of whose parameters you wish to
measure. Keep the probe far from elements that might interfere with measurement such as: heat or
sources of cooling, walls, air-streams, etc. Avoid temperature drops that might cause condensation.
A reading taken when no heat drop occurs is practically immediate. In contrast, in conditions
involving heat drops, it is necessary to wait until the sensors and their housing have reached a
thermal equilibrium in order to prevent heat irradiation or absorption on the relative humidity
sensor, which would cause a faulty measurement. Since temperature affects relative humidity; move
the probe like a fan in order to speed the response time in the presence of heat drops.
The calibration of the humidity/temperature sensor by the user is not required.
The humidity sensor is calibrated in our laboratory at 23°C at the points of 75%RH, 33%RH
and 11.4%RH. On request, the probes can be checked at different isotherms.
The temperature sensor is calibrated in the factory and the Callendar Van Dusen parameters
are recorded in the SICRAM module.
HD32.1
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V2.1
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