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RPM4-AD™ OPERATION AND MAINTENANCE MANUAL
7.2
UNIT CONVERSION
7.2.1
PRESSURE
RPM4-AD 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.
Table 33 provides the conversion coefficients used by RPM4-AD to convert numerical values
expressed in SI units to corresponding values expressed in other units.
Pa
mbar
hPa
kPa
bar
mmWa @ 4°C
mmHg @ 0°C
psi
psf
inWa @ 4°C
inWa @ 20°C
inWa @ 60°F
inHg @ 0°C
kcm
mTorr
Torr
user
ft
m
kts
km/h
mph
mach
7.2.2
ALTITUDE
Quantities
"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. RPM4-AD 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 Table 33 above. For altitude expressed in meters,
meters are converted to feet using 1 m = 3.28084 ft.
The following formulas are used to convert altitude in ft (H) into pressure (P) in inHg and from
pressure to altitude. There are three different equations depending on the range.
© 2005-2007 DH Instruments, a Fluke Company
Table 33. Pressure unit of measure conversion coefficients
TO CONVERT FROM Pa To
Pascal
millibar
ector Pascal
kilo Pascal
Bar
millimeter of water
millimeter of mercury
pound per square inch
pound per square foot
inch of water
inch of water
inch of water
inch of mercury
2
kilogram force per centimeter square
milliTorr (micron of mercury
Torr (millimeter of mercury)
User
feet of altitude
meter of altitude
knots
kilometers per hour
miles per hour
mach number
expressed
in
units
Page 134
MULTIPLY BY
1.0
1.0 E-02
1.0 E-02
1.0 E-03
1.0 E-05
1.019716 E-01
7.50063 E-03
1.450377 E-04
1.007206 E-06
4.014649 E-03
4.021732 E-03
4.018429 E-03
2.953 E-04
1.019716 E-05
7.50063
7.50063 E-3
User defined coefficient
see Section 7.2.2
see Section 7.2.2
see Section 7.2.3
see Section 7.2.3
see Section 7.2.3
see Section 7.2.3
of
altitude
follow
MIL-STD-859A
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