Fluke A20M-AF ユーザーズマニュアル
3. OPERATION
Page 55
© 2007 DH Instruments, a Fluke Company
<7intern>
Access internal functions including on-board barometer viewing, read rate adjustment, incident
log viewing (see Section 3.5.7).
log viewing (see Section 3.5.7).
<8cal>
View and adjust RPM4 Q-RPT and barometer calibration coefficients (see Sections 3.5.8, 5.2, 5.3).
<9reset>
Access RPM4’s various reset functions (see Section 3.5.9).
3.5.1
<1A
UTO
Z>
PURPOSE
To turn ON and OFF the AutoZ function that offsets the RPM4 Q-RPT readings relative to a
reference value in order to compensate for possible Q-RPT zero drift between full
recalibrations. To view and adjust the value of the AutoZ offset.
reference value in order to compensate for possible Q-RPT zero drift between full
recalibrations. To view and adjust the value of the AutoZ offset.
To RUN the AutoZ routine that rezeroes the Q-RPT, use [AutoZ] (see Section 3.3.9).
PRINCIPLE
AutoZ Purpose and Principle
The main component of the change over time of the RPM4 Q-RPTs is change in zero or
offset, independent of span. Offsetting or “rezeroing” RPM4 Q-RPTs relative to a reference
between recalibrations allows measurement uncertainty specifications to be maintained with
less frequent full calibrations. The RPM4 AutoZero function (AutoZ) provides full on-board
support for the rezeroing process to simplify its regular application by the user.
offset, independent of span. Offsetting or “rezeroing” RPM4 Q-RPTs relative to a reference
between recalibrations allows measurement uncertainty specifications to be maintained with
less frequent full calibrations. The RPM4 AutoZero function (AutoZ) provides full on-board
support for the rezeroing process to simplify its regular application by the user.
The AutoZero function uses three values:
1. P
std,0
: The pressure value indicated by the AutoZ reference, the device that is acting as the
reference relative to which to offset the RPM4 Q-RPT.
In absolute measurement mode, the pressure at which AutoZ is performed is normally
atmospheric pressure and the P
atmospheric pressure and the P
std,0
value can be supplied a) by manual entry, b)
automatically from a DHI RPMx connected to RPM4’s COM2 communications port, or c)
automatically from the Lo Q-RPT for the Hi Q-RPT.
automatically from the Lo Q-RPT for the Hi Q-RPT.
In gauge measurement mode, P
std,0
is always zero (atmospheric pressure) which is
supplied by definition when the Q-RPT is vented to atmosphere.
2. P
u,0
:
The pressure reading of the Q-RPT, with no AutoZ offset, at the time AutoZ is
performed.
3. P
offset,G
and P
offset,A
: The difference between the reading of the Q-RPT with no AutoZ offset
(P
u,0
) and the AutoZ standard (P
std,0
) for gauge (
G
) and absolute(
A
) measurement mode:
P
offset
= P
u,0
- P
std,0
P
offset
represents the difference between the Q-RPT reading (P
u,0
) and the AutoZ standard
(P
std,0
). The AutoZ function manages the determination, storage and application of P
offset
to
correct the zero offset in absolute and gauge measurement modes.
When the Q-RPT is calibrated, P
offset
is set to zero. P
offset
is then redetermined at regular
intervals using the AutoZ function. The most recent value of P
offset
is applied to the Q-RPT
reading to correct for zero drift.
The AutoZ function can be turned ON and OFF. Table 5 summarizes the effect of AutoZ ON
and OFF in absolute and gauge measurement modes.
and OFF in absolute and gauge measurement modes.
AutoZ in absolute measurement mode
The RPM4 A70M/A20M-AF Q-RPTs are intrinsically absolute. They have an evacuated and
sealed reference and naturally measure absolute pressure (difference from vacuum).
sealed reference and naturally measure absolute pressure (difference from vacuum).
In absolute measurement mode, the source of P
std,0
must be an absolute pressure, nominally
atmospheric pressure, with uncertainty significantly better than that of the Q-RPT that is