Fluke HPMS - Manual (Page 48)

RPM4/HPMS A70M/A20M-AF OPERATION AND MAINTENANCE MANUAL
© 2007 DH Instruments, a Fluke Company Page 38
3.3.7 [HEAD]
 PURPOSE
To cause a pressure fluid head correction to be added to or subtracted from the pressure
measured by the RPM4 reference pressure transducer in order to predict the pressure at a
height other than the RPM4/HPMS’s reference level.
 PRINCIPLE
RPM4/HPMS measures gauge or absolute pressure at the height of the rear panel TEST port.
Frequently, when performing a calibration or test, the device or system under test is at a different
height than the RPM4/HPMS’s TEST port. This difference in height, frequently called head, can
cause a significant difference between the pressure measured by the RPM4/HPMS at its TEST
port height and the pressure actually applied to the device under test which is at a different height.
In this case, it is useful to make a head correction to the pressure measured by the RPM4 in order
to predict the pressure actually applied at a different height.
RPM4 can accurately determine “head” pressures for gases (nitrogen, helium and air) and
liquids (oil, water) as the pressurized medium. In calculating the head value, standard gravity
(9.80665 m/s
2 ) is used. Gas densities are calculated from the selected gas’s standard
density correcting for temperature of 20°C and the measured pressure using the gas’s
compressibility factor to 100 MPa (15 000 psi) and extrapolated above 100 MPa. Oil density
is taken to be 850 kg/m
3
, the density of typical calibration oils at 20°C. Water density is taken
to be 998.2321kg/m
3
(20°C). A custom liquid density may also be specified.
The [HEAD] function key is used to specify the height difference between the RPM4/HPMS
TEST port and another height. Entering a height of zero turns the function off. The height
units and the test medium can be changed using [SPECIAL], <3Head> (see Section 3.5.3).
As a general rule with RPM4 A20M/A70M-AF, use of the HEAD function to assure in
tolerance measurements with RPM4 A70M/A20M-AF is necessary only when the head exceeds 10
in. (25 cm) if the medium is a gas.
 OPERATION
To access the HEAD function, press [HEAD]. The display is:
1. Edit field for head height.
2. Test gas currently specified for the head correction.
Edit head height:
+ 8 in N2
Edit the head height to the desired value. Press [ENT] to return to the MAIN RUN screen
with the new head correction active. Press [ESC] to return with no changes.
The reference height of the RPM4
pressure measurement is the middle of the
RPM4 TEST port. The head height should be
entered as a positive value if the device or
system under test is higher than the RPM4
and negative if it is lower.
The HEAD function is NOT range specific. The HEAD ON or OFF status remains the same
as Q-RPTs and ranges are changed. Edits made to the head settings are independent of active
range or Q-RPT.