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3. OPERATION
Page 61 © 2004-2007 DH Instruments, a Fluke Company
“line pressure”. The following simple recommendations will help assure that you use this
feature to best advantage.
• In gauge and differential 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 atmospheric reference.
• To assure operation within measurement uncertainty specifications (see Section 1.2.2),
run AutoZ whenever vented in gauge mode, whenever the line pressure is changed in
differential mode and at least every 30 days or when RPM4 has been exposed to
temperature changes exceeding 15 ºC (36 ºF) in absolute mode.
• 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 ± 0.01 % FS barometer is roughly 10 times better than an ± 0.01 % 1 MPa (150 psi)
Q-RPT because the Q-RPT/barometer pressure ratio is 10:1. The measurement
uncertainty comparison should be made at 30 % of span for both standard class and
premium class Q-RPTs. Though it may not be practical and generally is not necessary,
the best possible reference with which to run AutoZ in absolute measurement mode is a
gas operated piston gauge (such as a DHI PG7601) applying atmospheric pressure to
the RPM4 test port. The best day to day reference is a properly calibrated DHI RPM4
with a BA100K Q-RPT interfaced directly as an external device to the RPM4 COM2 port.
• In absolute measurement modes: Allow the RPM4 to stabilize at atmospheric pressure
and ambient temperature for 10 to 15 minutes before running AutoZ.
OPERATION
The AutoZ function and values are Q-RPT AND measurement mode (gauge/negative gauge
or absolute) specific.
To RUN the AutoZ routine that rezeroes the Q-RPT, use [AutoZ] (see Section 3.3.9).
To access the RPM4 AutoZ function press [SPECIAL], <1AutoZ>. The display is:
1. Active Q-RPT designator.
2. Indication of active measurement mode (<abs> for absolute,
<gage> for gauge and negative gauge, <dif> for differential).
3. Indication of whether AutoZ is currently ON or OFF for this
Q-RPT and measurement mode.
1off 2view Hi
3edit abs ON
Select <1off> (or <1on>) to change the AutoZ status for the current Q-RPT and
measurement mode from ON to OFF or vice versa.
AutoZ ON is indicated by a <z> in the MAIN RUN screen, top line, fourth character from
the right. When AutoZ is OFF, the character is blank.
Select <2view> to view the current value of P
offset
for the active Q-RPT and measurement mode.
P
offset
should be zero when the RPM4 is new or has just been calibrated. P
offset
should be
roughly equal to atmospheric pressure for an Axxx (absolute) Q-RPT operating in gauge mode.