PG7000™ OPERATION AND MAINTENANCE MANUAL
© 1998-2008 DH Instruments, a Fluke Company
Page 36
Once PG7000 has been set up, it is used in day-to-day operation either to define pressures applied to a
device or system under test or to measure a stable pressure. To interface with the PG Terminal, the operator:
Selects the appropriate piston-cylinder to cover the pressure range (see Section 3.11.1.5).
Selects the desired pressure unit of measure (see Section 3.9.3).
Selects the desired pressure measurement mode (gauge, absolute, differential) (see Section 3.9.4).
Sets the head difference between the PG7000 and the device under test (see Section 3.9.7).
Selects
mass to pressure
or
pressure to mass
operating mode (see Section 3.9.12).
Enters a pressure to define or a current mass load to calculate (see Section 3.9.11.1 and 3.9.11.2).
Loads masses by hand or with optional AMH automated mass handler, floats piston and defines
pressure.
3.1.1
GAS OPERATED, LIQUID LUBRICATED PISTON-CYLINDER
OPERATING PRINCIPLE (PG7202)
PG7202 provides very high pressure gas pressure operation using a unique gas operated,
liquid lubricated piston-cylinder system.
The principle of operation of the gas operated, liquid lubricated piston-cylinder is simple but
very effective (see Figure 6). The measured gas pressure, Pg, is applied to the bottom of the
piston and to the top of a liquid reservoir located around the cylinder. The reservoir is
connected to the gap between the piston and the cylinder through lateral holes near the
bottom of the cylinder, allowing liquid from the reservoir to enter the gap. The pressure of the
liquid in the gap, Pl, is equal to the gas pressure Pg, plus the liquid head, h. Therefore, the
liquid pressure in the gap is always higher than the gas pressure by the amount of the liquid
head regardless of the gas pressure value. Since h is small and the space between the
piston and cylinder is typically < 1 micron, the bleed of liquid from the bottom of the cylinder
towards the gas pressure is extremely small. The mounting post of the 7202 piston gauge is
configured so this minute amount of liquid drops directly into a sump that is deadened (see
Section 5.2.4, 3.1.1) and not in the flow path of test gas into and out of the system. Though
molecules of the liquid may migrate through the gas, no significant contamination of the test
system occurs. Because the liquid reservoir is contained in the piston-cylinder module,
piston-cylinders can be removed and installed in the PG7202 piston gauge platform with no
loss of liquid from the reservoir. All PC-7200 piston-cylinder modules can be delivered using
Krytox, a fluorinated synthetic fluid, to lubricate the piston-cylinder in applications where the
system must remain perfectly free of hydrocarbons (e.g. when calibrating instrumentation for
oxygen service).
PC-7200 gas operated, liquid lubricated piston-cylinder modules are delivered with
their lubricating liquid reservoir drained. The reservoir must be filled prior to using the piston-
cylinder module and then regularly when used (see Section 5.3.3)
