Fluke RPM4 manual Head, Psi a zHi, Conventional main run screen first line Clean second line

RPM4™ OPERATION AND MAINTENANCE MANUAL

OPERATION

To activate the Clean DISPLAY press [DISPLAY], <7Clean>. Pressing <7Clean> returns to the main run screen with the Clean DISPLAY active.

With the Clean DISPLAY active the main run screen is:

1.Conventional main run screen first line.

2.“Clean” second line.

99.135 psi a zHi

To go to a DISPLAY other than Clean, press [DISPLAY] and make a new DISPLAY choice (see Section 3.3.6).

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’s reference level.

PRINCIPLE

RPM4 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’s TEST(+) port. This difference in height, frequently called head, can cause a significant difference between the pressure measured by the RPM4 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/s2) 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/m3, the density of typical calibration oils at 20°C. Water density is taken to be 998.2321kg/m3 (20°C). A custom liquid density may also be specified.

The [HEAD] function key is used to specify the height difference between the RPM4 TEST(+) port and another height. Entering a height of zero turns the function off. The height unit and the test fluid are specified by pressing [SPECIAL], <3Head> (see Section 3.5.3).

Use of the HEAD function to assure in tolerance measurements is most important in low absolute pressure ranges. Specifying the head height within ± 5 cm (2.5 in.) is adequate to assure that, even in the worst case, the uncertainty on the head correction will be insignificant relative to the tolerance on the measurement.

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