PG7000™ OPERATION AND MAINTENANCE MANUAL
© 1998-2008 DH Instruments, a Fluke Company
Page 84
PRINCIPLE
The piston floating routines of PG7302 or PG7307 oil operated piston gauge using a
PPCH automated pressure controller are highly dependent upon the volume of the test
system into which pressure is being controlled. The VOL function is used to specify
the test volume so that the PG7302 or PG7307 may scale the PPCH rates properly for
the volume.
Operating with an improperly specified volume will cause the piston floating
routine to be either very slow (specified volume to small) or to overshoot
(specified volume too large).
If the test system volume is not known, the PPCH volume determination
function may be used to measure it. This function is run directly from the PPCH
front panel (see the PPCH Operation and Maintenance Manual, {INTERNAL],
<1CONFIG>).,
The test volume can be read or set remotely (see Section 4.3.4, ).
OPERATION
To view or set the test volume, press
[GEN]
,
<7vol>
.
The current volume value is displayed. The value is in cubic centimeres (cc).
The default volume is 30 cc. The maximum volume is 300 cc.
Edit the volume value if desired.
3.9.10
[RES]
PURPOSE
To set the resolution with which PG7000 loads mass in response to pressure or mass
commands (see Section 3.9.12).
PRINCIPLE
PG7000 piston-cylinders are sized such that there is a whole number, nominal relationship
between mass loaded on the piston in kilograms [kg] and the pressure at which the piston will
float in kilo Pascal [kPa] or Mega Pascal [MPa]. This relationship is called the
pressure
to
mass conversion coefficient
and is expressed as kPa/kg or MPa/kg. The
pressure to mass
conversion coefficient
is marked on the cap of each piston.
PG7000 mass sets are made up of masses in multiples and submultiples of the kilogram
making it simple to load mass values rounded to 0.01 g, 1 g, 10 g or 0.1 kg.
When using PG7000 to define pressure, the desired pressure value is entered (see Section
3.9.11) and PG7000 prompts the user with the mass value to be loaded. Due to the many
variables that influence the exact pressure to mass relationship for a piston-cylinder
(even though there is nominally a whole number mass to pressure relationship) the mass
value to load to reach exactly the pressure requested is always an odd value. Therefore,
defining the exact pressure value requested always requires loading mass with 0.01 g
resolution.
When it is acceptable for the pressure values defined to not be exactly the nominal pressure
value of the point, operation can be simplified and mass loading errors can be reduced by
loading mass with a lower level of resolution and using the pressure that the lower level
resolution mass load generates. For example, on a piston-cylinder with a nominal pressure to
mass relationship of 10 kPa/kg, defining a pressure of exactly 100 kPa, nominally requires