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The Humidity Generator

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The Humidity Generator

The RICI advanced calibration laboratory, outfitted with cutting-edge technology, caters to the company’s clients across the Middle East. Our senior management’s commitment to offering tertiary services is exemplified by the Thunder Scientific “two-pressure” humidity generator.

Humidity values are defined by this generator for instrument calibration, evaluation, verification and environmental testing. The humidity generator determines humidity calibration accuracy and detects humidity sensitivity by subjecting the sensing system to a variety of humidity levels; performs operational checks such as the sensing system’s capacity to correctly calculate and display other humidity parameters; and it determines the repeatability, stability, hysteresis and drift characteristics of various humidity sensing systems.

The defining equation to calculate relative humidity (RH) by the humidity generator is as follows:

RH = Pc/Ps* Es/Ec* Fs/Fc* 100

Where:

Pc=Chamber Pressure

Ps=Saturation Pressure

Es=Saturation Vapour Pressure at Saturation Temperature

Ec=Saturation Vapour Pressure at Chamber Temperature

Fs=Enhancement Factor at Saturation Temperature and Pressure

Fc=Enhancement Factor at Chamber Temperature and Pressure

100=Nominal Saturator Efficiency

The theory behind calculating the relative humidity can be understood by the dry bulb, wet bulb and dew point temperatures analysis.

 

The Dry Bulb temperature, also known as “air temperature”, refers to the ambient air temperature and is referred to as such because the air temperature is measured by a thermometer and is not affected by the moisture in the air.

The “Wet Bulb” temperature is the adiabatic saturation temperature and can be measured by using a thermometer with the bulb wrapped in wet muslin. The adiabatic evaporation of water from the thermometer bulb and the cooling effect is the wet bulb temperature. It is lower than the dry bulb temperature in the air. The rate of evaporation from the wet bandage on the bulb, and temperature difference between the dry bulb and wet bulb depends on the humidity of the air, such as: when air contains more water vapour, evaporation from the wet bulb is reduced.

The Wet Bulb temperature is always between the Dry Bulb temperature and the Dew Point, which is the temperature where water vapour starts to condense (the temperature at which air becomes completely saturated).

 

To sum up:

  • If the dew-point temperature is close to the dry air temperature – the relative humidity is high
  • If the dew point is well below the dry air temperature – the relative humidity is low

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