PPCH™ OPERATION AND MAINTENANCE MANUAL
© 2009 DH Instruments, a Fluke Company
Page 76
In gauge measurement mode, execution of the AutoZ function to update the value of
P
atm,0
,
occurs automatically whenever PPCH is vented. Updating
Δ
P
atm
occurs automatically
continuously during unvented operation.
Take care to consider fluid heads in gauge mode operation. The fluid head when vented may
be different from the fluid head at other pressures due to the height of the reservoir to which the
Q-RPT is connected when vented (see Section 3.3.7,
PRINCIPLE).
AutoZ ON/OFF
The AutoZ function can be turned ON and OFF, separately for gauge and absolute
measurement modes. Table 11 summarizes the effect of AutoZ ON and OFF for PPCH
Q-RPTs in absolute and gauge measurement modes.
Table 11.
AutoZ ON and OFF
MEASUREMENT
MODE
AutoZ
STATUS
P
offset
APPLIED
Δ
P
atm
APPLIED
AutoZ
ROUTINE
RUNS
ON YES
When initiated
by operator
Absolute
OFF NO
Not Applicable
Not available
ON YES
Gauge
OFF
YES
NO
Automatically
when PPCH in
VENT condition
Recommendations for the Use of the AutoZ Function
The AutoZ function provides a powerful and easy to use tool for improving the stability over
time of PPCH internal and external Q-RPTs and maximizing the recalibration interval by
compensating for change in zero between full recalibrations. The following simple
recommendations will help assure that you use this feature to best advantage.
In
gauge measurement
mode:
Always leave AutoZ ON when operating.
In
absolute measurement
mode: Always leave AutoZ ON when operating
if
the AutoZ routine
has been run regularly using a valid Z
offset
reference.
In
absolute measurement
mode:
Run AutoZ at least every 30 days or when RPM4 has been
exposed to temperature changes exceeding 15 ºC (36 ºF).
In
absolute measurement
mode: Run AutoZ only when a reference whose measurement
uncertainty is known to be significantly better than that of
the Q-RPT to be AutoZeroed is available. Keep range
ratios in mind when comparing uncertainty.
A ± 0.1 % FS barometer is roughly 100 times better than
a ± 0.01 % 100 MPa (15 000 psi) Q-RPT because the Q-
RPT/barometer pressure range ratio is 1000:1.
In
absolute measurement mode:
Allow the PPCH to stabilize at atmospheric pressure and
ambient temperature for 10 to 15 minutes before running
AutoZ.
In
absolute measurement mode:
Take care to properly consider fluid heads on the
Q-RPTs and the AutoZ reference.
OPERATION
The AutoZ function and values are Q-RPT AND measurement mode (absolute, gauge)
specific.
