3. OPERATION
Page 57
© 2005-2007 DH Instruments, a Fluke Company
<3head>
Set HEAD function gas and height unit of measure (see Section 3.5.3).
<4SDS>
View and set the temporary and full time ON/OFF and OPEN/CLOSED status of SDS for
Q-RPTs.
<5prefs>
View and set screen saver time, keypad sound frequency, unit ID number, time/date,
security protection level (see Section 3.5.5).
<6Punit>
Customize
the
[UNIT]
key unit of measure selections (see section 3.5.6).
<7intern>
Access internal functions including on-board barometer viewing, read rate adjustment, incident
log viewing (see Section 3.5.7).
<8cal>
View and adjust RPM4, Q-RPT and barometer calibration coefficients (see Sections
3.5.7.5, 5.2, 5.3).
<9reset>
Access RPM4’s various reset functions (see Section 3.5.9).
3.5.1
<1A
UTO
Z>
PURPOSE
To offset the RPM4-AD Q-RPTs readings relative to a reference value in order to
compensate for possible changes in Q-RPT zero between full recalibrations. In differential
measurement mode, to compensate for the difference between the reading of the Hi and Lo
Q-RPTs at the “line pressure” at which differential measurements are made.
To assure operation within measurement uncertainty specifications (see Section 1.2.2.1),
it is recommended that AutoZ be run (the value of P
offset
updated) whenever vented in
gauge mode, whenever the line pressure is changed in differential mode and at least every
30 days or when RPM4-AD has been exposed to temperature changes exceeding 15 ºC
(36 ºF) in absolute mode.
PRINCIPLE
AutoZ Purpose and Principle
The main component of the change over time of the RPM4-AD Q-RPTs is change in zero or
offset, independent of span. Offsetting or “rezeroing” RPM4-AD Q-RPTs relative to a
reference between recalibrations allows measurement uncertainty specifications to be
maintained with less frequent full calibrations. AutoZ is also used to compensate for the
difference between the Hi and Lo Q-RPT at the “line pressure” at which differential
measurements are made. The RPM4-AD AutoZero function (AutoZ) provides full on-board
support for the rezeroing process to simplify its 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-AD Q-RPT.
In absolute measurement mode
, the pressure at which AutoZ is performed is normally
atmospheric pressure and the
P
std,0
value can be obtained by RPM4-AD a) by manual
entry, b) automatically from a
DHI
RPMx connected to RPM4-AD COM2 communications
port, or automatically from the Lo 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.
In differential measurement mode
,
P
std,0
is the pressure indicated by the Lo Q-RPT
when the Hi and Lo Q-RPTs are connected to a common pressure.
2.
P
u,0
:
The pressure reading of the Q-RPT, with no AutoZ offset, at the time AutoZ is
performed.
