3. GENERAL OPERATION
Page 67
© 1998-2008 DH Instruments, a Fluke Company
With the system’s BYPASS valve OPEN (see Figure 10), use the INLET and/or
VENT valve and the high side variable volume to adjust the pressure to float the
piston of the
tare
PG7000. This should cause the
reference
PG7000 piston to
be at its bottom stop. Once the
tare
piston is floating, close the system’s
BYPASS valve and press
[ENTER]
. The next display is:
1.
Tare piston position.
2.
Reference piston position.
+1.2 mm –3.6 Set
T & R to + 1.0&[ENT]
Use the high and/or low side variable volume to set both pistons to a position just
above + 1.0 mm. Ensure that both pistons are rotating. As both pistons fall
through the + 1.0 position, press
[ENTER]
. PG7000 pauses for 5 seconds and
then measures the natural fall rates of both pistons for 30 seconds.
1.
Indication of tare piston position.
2.
Indication of reference piston position.
3.
30 second count down.
T+1.0 mm R+1.0
Finding rates 29
Wait for the 30 second timer to count down while the measurements are made.
Be sure not to interfere with the free movement of the piston-cylinders during
the countdown. After the countdown completes, the results are displayed:
1.
Average fall rate of the taring piston.
2.
Average fall rate of the reference piston.
3.
Difference between the reference and taring
piston fall rates (R - T). This is the “natural fall
rate difference”.
T-0.9 mm/min R-1.1
∆
-0.2 Save 1yes 2no
The “natural fall rate difference” is the difference between the fall rates of the
two pistons when they are floating naturally at the line pressure. When performing
the crossfloat between the pistons in the next step of line pressure setting, the
objective will be to adjust the mass of the tare piston until the “crossfloat fall rate
difference” measured with the system’s BYPASS valve open is equal to the “natural
fall rate difference” measured with the BYPASS closed.
Select
<2no>
to repeat the “natural fall
rate difference” measurement. Select
<2yes>
to accept the “natural fall rate
difference” value and continue to the
second step of line pressure setting which
is crossfloating the two piston-cylinders.
The display is:
Open bypass and
[ENTER] to xfloat