DH Instruments PG7000, Руководство по эксплуатации и обслуживанию

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PG7000™ OPERATION AND MAINTENANCE MANUAL
© 1998-2008 DH Instruments, a Fluke Company Page 210
PISTON head: Calculates and applies a fluid head correction to compensate for
the difference between the current piston position and the PG7000’s reference
level (see Section 3.11.3.4).
The DUT head is calculated following:
( )
P a f H
gh ρ ρ P
P
− =
Where:
P
H
P
, Piston head [Pa] = fluid head correction applied to calculate defined pressure.
ρ
f
, fluid density [kg/m
3
] = Density of test fluid at current pressure.
ρ
a
, air density [kg/m
3
] = density of ambient air calculated using current ambient
pressure, temperature and relative humidity (values as
specified in the active SETUP file, see Section 3.10).
Assumed to be zero when operating in absolute with a
vacuum reference mode. Calculated using static pressure
density measured by RPM in PG7601 differential mode.
g
, gravity [m/s
2
] = acceleration due to gravity (value as specified in the active
SETUP file, see Section 3.10).
h
P
, piston height [m] = Height of the current piston position above PG7000
reference level.
7.2.3.2 OVERALL FLUID HEAD CORRECTION
The overall fluid head correction for each PG7000 mode results from combining
the three head components. In general, overall head correction is given by:
P atm DUT
H H H H
P P P P
+ − − =
Gauge mode:
( ) ( )
P a f D a f HG
gh gh P
ρ ρ ρ ρ
− + − − =
Absolute mode by adding atmospheric pressure: Air density is zero for all
components except for the ATM head which is used to compensate for
barometer height.
P f B as D f HA
gh gh gh P
ρ ρ ρ
+ − − =
Absolute mode with vacuum reference: Air density is zero for all terms and
no barometer is used.
P f D f HA
gh gh P
ρ ρ
+ − =
High line differential mode: Subtraction of tare head correction from reference
gives total differential head correction, assuming both tare and reference
PG7000 levels are at the same height. Note that (
P+
Δ
P
) represents fluid
properties evaluated at line pressure plus differential pressure. Also note that
the barometer head corrections cancel out.
( ) ( )
g h h h g P P P
T P R P P P P P T R
P f P f D f f HG HG HD
ρ ρ ρ ρ
− + − − = − =
Δ + Δ +
Differential mode: Head correction is the same as for absolute mode with
vacuum reference. Head correction for the height of the RPM is unnecessary
through the use of the RPM offset.
P f D f HA
gh gh P
ρ ρ + − =