ADM-860C 04/14/0850
13.0 CORRECTION FACTORS AND CONVERSION FORMULAS
13.1 BAROMETRIC PRESSURE DENSITY CORRECTION - LOCAL DENSITY
The ADM-860C AirData Multimeter automatically corrects air flow and velocity readings to represent local density
cfm or fpm as affected by barometric pressure.
13.2 BAROMETRIC PRESSURE DENSITY CORRECTION - STANDARD DENSITY
Standard density air flow or velocity is calculated as if the same mass flow (lb/min) existed at standard conditions
(29.92 in Hg & 70
/ F). Standard density (mass flow equivalent) results may be obtained by using one of the
following conversion formulas:
13.2.1 STANDARD DENSITY - TEMPROBE USED
If the TemProbe was used during the measurement, the conversion formula for standard density is:
Where: P
b
= local barometric pressure (in Hg)
/ F = measured temperature of the airstream
13.2.2 STANDARD DENSITY - TEMPROBE NOT USED
If the TemProbe was not used during the measurement, the conversion formula is:
Where: P
b
= local barometric pressure (in Hg)
/ F = measured temperature of the airstream
13.3 TEMPERATURE DENSITY CORRECTION
Air flow and velocity readings are density corrected for the effect of temperature if the TemProbe temperature
sensor is used during flow or velocity measurements. If the temperature probe is not used, the meter calculates
the air density using an assumed temperature of 70
/ F. If the TemProbe sensor was not used during an air flow
measurement, the displayed reading must be corrected for the density effect of temperature as follows:
Where: / F = measured temperature of airstream.
13.4 RELATIVE HUMIDITY CORRECTION
The ADM-860C AirData Multimeter does not correct for the density effects of relative humidity on air flow and
velocity readings. The effect of minor variations in relative humidity on local air density (and therefore on flow
and velocity readings) is relatively small under normal room temperature conditions. The density effect of relative
humidity at higher temperatures and higher relative humidities may be more significant.
Local air density velocity and flow readings may be corrected for the density effects of relative humidity using the
formula shown below. This calculation requires the use of the vapor pressure, which must be looked up on a
Dew Point/Vapor Pressure conversion chart. The dew point may be measured directly using a very accurate
dewpointer. Psychrometric charts are also available for determining the dew point and may be used if the
ambient temperature and relative humidity are known. Note: If the vapor pressure is in metric units, the
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