3. OPERATION
Page 35 © 1998 DH Instruments, Inc.
the pressure measured by the PPC2 AF reference transducer in order to accurately predict
the pressure actually applied at a different height.
PPC2 AF can accurately calculate the "head" pressure for nitrogen, helium and air as the test
gas over its working pressure range. The HEAD function allows the height difference and test
gas to be specified and causes the resulting head pressure to be added to the pressure
measured at the TEST port.
The HEAD function key is used to turn the head correction function on and off and to specify
the height difference used to calculate the head pressure between the PPC2 AF TEST port
and the device under test. The height units and the test gas are specified under 2Head of the
SPECIAL menu (see Section 3.4.2).
Use of the HEAD function to assure in tolerance measurements is most important at low
absolute pressures. Specifying the head height within ± 5 in. (12.5 cm) is adequate to
assure that, even in the worst case, the uncertainty on the head correction will be
insignificant relative to the tolerance on the measurement.
OPERATION
To access the HEAD function, press the HEAD function key. The display is:
1. Entry field for head height.
2. Test gas currently specified for the head correction.
Edit head height
+ 95 cm N2
Entering a value of zero turns the HEAD function off. Entering a value other than zero turns
the HEAD function on using the height entered. Pressing ESCAPE returns to the main run
screen with no change to the current setting.
When the HEAD function is “on”, it is indicated by “H” in the top line of the main run
screen (see Section 3.1.1).
The HEAD function is not range specific. The HEAD "on" or "off" status remains the same
as ranges are changed and edits made to the head specifications are independent of range.
To change units of height between inches and centimeters and to change the test gas
species, use 2Head under the SPECIAL menu (see Section 3.4.2).
The reference height of the PPC2 AF reference
pressure transducer is the middle of the
PPC2 AF TEST port. The head height should be
entered as a positive value if the device or
system under test is higher than the PPC2 AF
and negative if it is lower.
+
-
Reference Level
(TEST Port)
)
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