Honeywell Mini-AT, User Manual, Page: 13 / 156

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Page 13
Mini-AT User Guide
Correction Factors to Metered Volume
Ideal or perfect gases follow the relationship of Boyle’s Law for pressure effect and Charles’ Law for
temperature effect, which can be stated: The volume of any definite weight of a perfect gas varies
inversely with change in absolute pressure and directly with change in absolute temperature. The
equation for this relationship of the two laws is expressed as follows:
V1 P1 V2 P2
T1 T2
The Symbols V1, P1 and T1 refer to the original volume, pressure and temperature while V2, P2 and T2
refer to the volume, pressure and temperature of the new or changed conditions. Rearranging the
equation and rewriting subscripts, we can express it as follows:
Where: Vb = gas volume (cu. ft.) at base condition corrected
Pb = absolute base pressure (psia)
Tb = absolute base temperature (deg. R)
Vm = gas volume metered (cu. ft.) uncorrected
Pm = absolute meter pressure (psia)
Tm = absolute meter temperature (deg. R)
Pressure Factor Fp
The pressure factor (Fp) to apply to metered volume is expressed by the Boyle’s Law relationship as
follows:
Pm Meter pressure (PSIG) + atmospheric pressure (PSIA)
Fp
Pb Base pressure (PSIA)
Each increment of meter pressure represents a different pressure factor. As the flowing gas pressure (Pm)
changes, the Mini-AT automatically applies the pressure factor (Fp) to the metered volume (Vm).
Temperature Factor Ft
The temperature factor (Ft) to apply to metered volume is expressed by the Charles’ Law relationship
as follows:
Tb Base temperature, deg. F + 459.67
Ft
Tm Meter temperature, deg. F + 459.67
Each increment of meter temperature represents a different temperature factor. Therefore, as the
flowing gas temperature (Tm) changes, the Mini-AT automatically applies the temperature factor (Ft)
to the metered volume.
Pm Tb
Vb Vm
X X
Pb Tm