PG7000™ OPERATION AND MAINTENANCE MANUAL
© 1998-2008 DH Instruments, a Fluke Company
Page 76
the pressure defined by the PG7000 at its reference level in order to accurately predict the
pressure actually applied at a different height. The HEAD function allows this head
correction to be applied automatically for a variety of fluids based on operator entry of the height
difference. The fluid used and the HEAD function units of measure are set by pressing
[SPECIAL]
and selecting
<3head>
(see Section 3.11.3).
PG7000 can accurately determine
head
pressures for gases (nitrogen, helium and air) and
liquids (Di-2 ethylhexyl Sebacate oil, water and a user defined liquid) as the pressurized medium.
When gas is the test fluid, use of the HEAD function is most important at low
absolute pressures. In this case, specifying the head height within ± 0.2 in. (5 mm) is adequate
to ensure that, even in the worst case, the uncertainty on the head correction will be insignificant
relative to the tolerance on the PG7000 measurement. Use of the HEAD function to ensure
tolerance measurements is particularly critical when a liquid is the test fluid, due to the high
density of liquids. To determine when and how precisely a head correction for liquids must be
made, 0.03 psi/inch (90 Pa/cm) may be used as an estimation of the liquid head value.
Regardless of the head function’s setting, corrections are automatically applied to the
calculated reference pressure to compensate for the deviation between the current piston
position and the mid-stroke position (see Section 3.11.3.4).
The pistons of certain gas operated piston-cylinder modules are hollow. Due to their
irregular shape, for these pistons, the natural reference level is not at the bottom of the piston.
So that, in practice, the actual reference level is the same for all piston-cylinder modules, a
reference level offset is applied when a hollow piston is used. The reference level offset is included
in the piston-cylinder file (see Section 3.11.1.1) and corrects the reference level back to the
reference point marked on the mounting post.
OPERATION
To access the HEAD function, press
[HEAD]
. The display is:
1.
Test fluid currently specified for the head correction.
2.
Entry field for head height (1 to 999 cm or in.).
Edit DUT head height
95 cm N2
Entering a value of zero turns the HEAD function OFF. Entering a value other than zero
turns the HEAD function ON using the height entered. Pressing
[ESCAPE]
returns to the
main run screen with NO change to the current head setting.
Содержание PG7000
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