DH Instruments PPC4, Operation And Maintenance Manual

Page: 45 / 228

3. OPERATING PRINCIPLES
Page 33 © 2009 DH Instruments, a Fluke Company

PRINCIPLE
PPC4 measures gauge or absolute pressure at the height of the rear panel TEST(+) port.
Frequently, when performing a calibration or test, the device or system under test is at a
different height than the PPC4’s
TEST(+) port. This difference in height, frequently called
head , can cause a significant difference between the pressure measured by the PPC4 at its
TEST port height and the pressure actually applied to the device under test which is at a
different height. In this case, it is useful to make a head correction to the pressure measured
by the PPC4 in order to predict the pressure actually applied at a different height.
PPC4 can calculate head pressures for nitrogen, helium and air as the test gas over its working
pressure range. The HEAD function allows the height difference to be specified and causes
the resulting head pressure to be added to the pressure measured at the
TEST port.
The reference height of the PPC4 pressure
measurement is the middle of the PPC4
TEST port. The head height should be
entered as a positive value if the device or
system under test is higher than the PPC4
and negative if it is lower.
Note
•
Use of the Head function to ensure in tolerance measurements is most
important in low absolute pressure ranges. Specifying the head height
within ± 3 in. (7.5 cm) is adequate to ensure that, even in the worst case,
the uncertainty on the head correction will be insignificant relative to
the tolerance on the measurement.
•
The Head function is NOT range specific. The Head On or Off status
remains the same as ranges are changed. Edits made to the head
settings are independent of active range or Q-RPT.
•
In the PPC4 Basic Interface, when a head correction is being applied, it
is indicated by <h> in the top line of the Main Run Screen (see Section
4.1). The <h> is not shown when the head correction is zero.
•
In the PPC4 Advanced User Interface, the head height and fluid are
shown beside
Head: on the Main Run Screen (see Section 5.1).
•
When using external Q-RPTs in RPM4, it is recommended that the
RPM4 head height be adjusted to the reference level of the PPC4 before
connecting the RPM4. Then, the normal PPC4 reference level to UUT
head corrections can be made for all the Q-RPTs, whether internal or
external to PPC4.

OPERATION
For Basic Interface see Section 4.5.16.
For Advanced Interface see Section 5.7.6.3.
3.2.17 Purge

PURPOSE
To execute the PPC4 test system Purge function using the optional Self Purging Liquid Trap
(SPLT). Purge is used to collect and exhaust liquid contaminants from the device or system
under test before they reach the PPC4.