ScreenMaster RVG200
Paperless recorder
7 Configuration
134
OI/RVG200-EN
7.13.3 Relative humidity calculation
Relative humidity is calculated using the following formula:
Where:
A relative humidity (RH) calculation requires two inputs, one from a wet bulb sensor and one from a dry bulb
sensor. Both of these inputs are incorporated into the equation as analog.
RH tables are based on the use of an aspirated psychrometer that has an air velocity of at least 3.5 meters
(11.5 feet) per second across the bulb sensors.
Inputs used for wet and dry bulb measurement must be in the ranges 0 to 100 °C (32 to 212 °F). The result
must be set to 0 to 100.0 % RH.
Fig. 7.20 (page 135) is an example of configuring a math block to perform a relative humidity calculation.
VPSw = Saturation vapor pressure at wet bulb temperature
VPSd = Saturation vapor pressure at dry bulb temperature
Td = Dry bulb temperature
Tw = Wet bulb temperature
P = Total atmospheric pressure (1000 mbar)
A = Psychometric constant (6.66 x 10–4)
RH = % of relative humidity
RH
100
VPSw
AP
Td
Tw
–
–
VPSd
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