DH Instruments PPC3 - Table 8. Autoz on and off

PPC3™ OPERATION AND MAINTENANCE MANUAL
© 2002-2007 DH Instruments, a Fluke Company Page 60
the P
offset,G
value corresponding to atmospheric pressure. Gauge pressure is the measured
absolute pressure, P
u
, minus P
offset,G
.
P
gauge
= P
u
- P
offset,G
When AutoZ is ON, dynamic compensation for atmospheric pressure is also applied to
compensate for changes in atmospheric pressure between AutoZ updates (see Section 3.2.3).
The measured gauge pressure is calculated using ΔP
atm
to correct the value of P
offset.G
.
P
gauge
= P
u
- P
offset.G
- ΔP
atm
In gauge measurement mode with an Axxx RPT, execution of the AutoZ function to update
the value of P
atm,0
, occurs automatically whenever PPC3 is vented. Updating ΔP
atm
occurs
automatically continuously during unvented operation.
AutoZ in gauge measurement mode with a Gxxx or BGxxx Q-RPT
Q-RPTs with the designation Gxxx or BGxxx are intrinsically gauge. They have an
atmospheric reference port and measure gauge pressure (difference from atmosphere).
In gauge measurement mode the value of P
std,0
is always zero gauge pressure. Zero gauge
pressure, by definition, is applied to the Q-RPT when it is vented to atmosphere. In gauge
measurement mode, the AutoZ routine is run automatically whenever the PPC3 is in the
vented condition. This assures the regular automated updating of the P
offset,G
value.
When using a Gxxx Q-RPT in gauge measurement mode, with AutoZ ON, gauge pressure is
calculated as:
P
gauge
= P
u
- P
offset,G
AutoZ ON/OFF
The AutoZ function can be turned ON and OFF, separately for gauge and absolute
measurement modes. Table 8 summarizes the effect of AutoZ ON and OFF for different
Q-RPT types in absolute and gauge measurement modes.
Table 8. AutoZ ON and OFF
Q-RPT
TYPE
MEASUREMENT
MODE
AutoZ
STATUS
P
offset
APPLIED
ΔP
atm
APPLIED
AutoZ
ROUTINE
RUNS
ON YES
When initiated
by operator
Absolute
OFF NO
Not Applicable
Not available
ON YES
Axxx
(or utility
sensor)
Gauge or
negative gauge
OFF
YES
NO
Automatically
when PPC3 in
VENT condition
ON YES
Automatically
when PPC3 in
VENT condition
Gxxx
or
BGxxx
Gauge or
negative gauge
OFF NO
Not Applicable
No
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 PPC3 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 P
offset
reference.
• In absolute measurement mode: Run AutoZ at least every 30 days or when PPC3 has
been exposed to temperature changes exceeding 15 ºC (36 ºF).