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RPM4-AD™ OPERATION AND MAINTENANCE MANUAL
3. P
, P
offset,G
AutoZ offset (P
absolute(
P
represents the difference between the Q-RPT reading (P
offset
(P
). This value is used to correct the RPM4-AD Q-RPT so it agrees with the AutoZ
std,0
standard. The AutoZ function manages the determination, storage and application of P
to correct the Q-RPT in absolute, gauge and differential measurement modes.
When the Q-RPT is calibrated, P
intervals using the AutoZ function. The most recent value of P
reading to correct for change in zero.
The AutoZ function can be turned ON and OFF. Table 11 summarizes the effect of AutoZ
ON and OFF.
AutoZ in absolute measurement mode
RPM4-AD Q-RPTs are intrinsically absolute. They have an evacuated and sealed reference.
In absolute measurement mode, the source of P
atmospheric pressure, with uncertainty significantly better than that of the Q-RPT that is
being AutoZeroed.
When a Q-RPT is in absolute measurement mode with AutoZ ON, absolute pressure is
calculated as:
In absolute measurement mode, running the AutoZ function to update the AutoZ value
(P
), is initiated by the operator using [AutoZ] (see Section 3.3.9.2).
offset,A
AutoZ in gauge and negative gauge measurement modes, dynamic compensation for
atmospheric pressure
RPM4-AD Q-RPTs are intrinsically absolute but they are also used in gauge and negative
gauge
(difference
PRINCIPLE).
atmospheric pressure from the Q-RPT's absolute reading using AutoZ and by dynamically
compensating for changes in atmospheric pressure between opportunities for AutoZ to
execute (see Section 3.2.2).
In gauge measurement modes, the value of P
gauge pressure, by definition, is applied to the Q-RPT when it is vented to atmosphere.
Gauge pressure is the measured absolute pressure, P
When AutoZ is ON, dynamic compensation for atmospheric pressure is also applied to
compensate for changes in atmospheric pressure as measured by a barometer (ΔP
AutoZ updates (see Section 3.2.2). The measured gauge pressure is calculated using ΔP
to correct the value of P
In gauge measurement mode, running the AutoZ function to update the value of P
initiated by the operator using [AutoZ] (see Section 3.3.9.1). ΔP
is then updated continuously as new atmospheric pressure measurements are made by the
barometer.
© 2005-2007 DH Instruments, a Fluke Company
and P
: The difference between the reading of the Q-RPT with no
offset,A
offset,D
) and the indication of the AutoZ reference (P
u,0
) or differential (
) measurement mode:
A
D
offset
P
from
atmosphere)
Gauge measurement mode is achieved by subtracting the value of
P
gauge
.
offset.G
P
gauge
Page 58
P
= P
- P
offset
u,0
std,0
is set to zero. P
is then redetermined at regular
offset
must be an absolute pressure, nominally
std,0
= P
- P
abs
u
offset,A
measurement
modes
is always zero gauge pressure. Zero
std,0
, minus P
u
= P
- P
u
offset,G
= P
- P
- ΔP
u
offset.G
atm
) for gauge (
std,0
) and the AutoZ standard
u,0
offset
is applied to the Q-RPT
offset
(see
Section
3.3.3,
.
offset,G
) between
atm
atm,0
resets when AutoZ is run
atm
),
G
atm
, is
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