3. GENERAL OPERATION
Page 111
© 1998-2008 DH Instruments, a Fluke Company
3.11.1.15
SELECT MASS LOADING BELL
PURPOSE
To select the mass loading bell that is active and used by PG7000 in its mass
loading and defined pressure calculations.
OPERATION
To select the active mass loading bell set press
[SPECIAL]
,
<1PC/MS>
and
select
<3mass bell>
,
<5select>
.
3.11.2
<2PRESU>
PURPOSE
To customize the selection of pressure units that are available for selection from the UNIT
function key (see Section 3.9.3).
PRINCIPLE/OPERATION
See Section 3.9.3.1.
3.11.3
<3HEAD>
PURPOSE
To change DUT head configuration; to change the ATM head height; turn to turn the PISTON
head ON and OFF (PG7302 only).
PRINCIPLE
PG7000 supports three different fluid head correction functions.
1. There is a correction to consider the difference in height between the PG7000 reference
level and a device under test (see Section 3.9.7, PRINCIPLE). This head correction is
referred to as DUT head. The head height can be adjusted by pressing
[HEAD]
. The
head unit of measure and fluid are adjusted by pressing
[SPECIAL]
and selecting
<3head>
,
<1fluid>
and
<2unit>
.
2. The second head function is the head correction for the PG7000 reading of atmospheric
pressure that is used to calculate air density and/or to add to atmospheric pressure in absolute
by adding atmosphere mode. The barometer reading atmospheric pressure may not be at the
same height as the piston reference level and, if so, a head correction is needed to determine
atmospheric pressure at the piston reference level. This head correction is referred to as ATM
head. The ATM head height can be edited by pressing
[SPECIAL]
and selecting
<3head>
,
<3atm>
. The ATM head is only applied to internal or external barometer readings. It is not
applied to normal or user values of atmospheric pressure.
3. The third head function is the automated correction for the piston position, referred to as
PISTON head. The PG7000 reference level marked on the piston-cylinder module
mounting post is the level at which pressures are defined when the piston is in midstroke
position. But it may not always be practical to make measurement with the PG7000
piston exactly in its midstroke position. In fact, the piston position is
Ready
within a limit
band above and below midstroke (see Section 3.4.1). As the piston moves away from
midstroke, the pressure definition reference level moves proportionally. PG7000’s
automated correction for piston position calculates the head pressure corresponding to
the deviation in piston position from midstroke and compensates the defined pressure
back to midstroke. In this way, the defined pressure calculated by PG7000 is always the
pressure at the reference level marked on the mounting post, even if the piston is not at
midstroke position. The PISTON head function can be turned ON and OFF by pressing
[SPECIAL]
and selecting
<3head>
,
<4piston>
.
See Section 7.2.3 for information on calculation of the three fluid head correction functions.
