9. APPENDIX
Page 141 © 1998 DH Instruments, Inc.
9.3 UNIT CONVERSION
9.3.1 PRESSURE
PPC2 AF performs all internal calculations in SI units. Numerical values input or output in
other units are converted to SI immediately after entry and back to other units just before
output as needed.
The tables below provide the conversion coefficients used by PPC2 AF to convert numerical
values expressed in SI units to corresponding values expressed in other units.
TO CONVERT FROM Pa To MULTIPLY BY
Pa
Pascal
1.0
mbar
millibar
1.0 E-02
kPa
kilo Pascal
1.0 E-03
bar
bar
1.0 E-05
mmWa @ 4°C
millimeter of water
1.019716 E-01
mmHg @ 0°C
millimeter of mercury
7.50063 E-03
psi
pound per square inch
1.450377 E-04
psf
pound per square foot
1.007206 E-06
inWa @ 4°C
inch of water
4.014649 E-03
inWa @ 20°C
inch of water
4.021732 E-03
inWa @ 60°F
inch of water
4.018429 E-03
inHg @ 0°C
inch of mercury
2.953 E-04
kcm
2
kilogram force per centimeter square
1.019716 E-05
ft
feet of altitude
see Altitude Note below
m
meter of altitude
see Altitude Note below
Altitude Note: Quantities expressed in units of altitude follow MIL-STD-859A “Static
Pressure, p, in Inches of Mercury for Values of Pressure Altitude, H, in Geopotential
Feet.” MIL-STD-859A provides tables of pressure in inches of mercury as a function of
altitude in feet. PPC2 AF uses a set of equations to model the pressure/altitude relationship.
The worst case deviation between the MIL-STD-859A table and the calculated pressure
is 0.0001 inches of mercury (0.3 Pa). The pressure quantity expressed in inches of
mercury is converted to Pascal following the table above. For altitude expressed in
meters, meters are converted to feet using 1 m = 3.28084 ft.
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