Fluke A20M-AF Manual Do Utilizador

 

Page 19 

© 2007 DH Instruments, a Fluke Company 

The RPM4 A70M/A20M-AF Q-RPTs are intrinsically absolute but they are also used for gauge 
measurement mode (see Section 3.3.3, 

 PRINCIPLE).  Gauge measurement mode is achieved by 

subtracting the value of atmospheric pressure, P

, from the Q-RPT’s absolute reading 

using AutoZ (see Section 3.2.2).  The AutoZ routine that measures P

, is run by pressing 

[AutoZ] whenever RPM4 is in the vented condition.  This assures the continuous updating of the 
P

 value corresponding to atmospheric pressure.  Gauge pressure is the measured absolute 

pressure, P

, minus the atmospheric offset, P

. 

However, atmospheric pressure may change between opportunities to run AutoZ and update 
the value of P

, for example when running an extended test without venting.  RPM4 uses 

dynamic compensation for atmospheric pressure to correct for changes in atmospheric 
pressure between opportunities to run AutoZ and update P

.  When AutoZ runs, and 

 is determined, the reading of RPM4’s on board barometer, P

, is also recorded.  

Later, when no longer vented, the change in atmospheric pressure, 

, since P

 was 

updated, is the difference between the current barometer reading, P

, and the barometer 

reading at the time of AutoZ execution, P

: 

Dynamic compensation for atmospheric pressure uses 

 to correct the value of P

, 

thus always compensating real time for changes in atmospheric pressure: 

The additional uncertainty in gauge pressure mode due to the dynamic compensation for 
atmospheric pressure technique is a function of the resolution and short term stability of the 
on-board barometer, not its absolute measurement uncertainty.  This additional uncertainty is 
completely insignificant in the range of pressure covered by the RPM4 A70M/A20M-AF. 

RPM4 A70M/A20M-AF has two Quartz Reference Pressure Transducers (Q-RPTs).  The A70M 
(10 000 psi) Q-RPT is designated the Hi Q-RTP.  The A20M (3 000 psi) Q-RPT is designated 
the  Lo  Q-RTP.  Which Q-RPT is currently active is continuously by characters in the upper 
right hand corner of the MAIN RUN screen and most other screens. 

 

Each RPM4 Q-RPT has a default range which is its maximum range.  Additional ranges, lower 
than the Q-RPT’s maximum, may also be created using AutoRange and AutoTest (see 
Section 3.3.4, 3.3.10).  Ranges created using AutoRange are temporary but may be saved with 
all their settings for reactivation (see Section 3.4.1.1).  

An RPM4 range is identified by a range screen showing the Q-RPT used by the range, its current unit 
of measure and its full scale pressure in gauge and absolute measurement modes. The range 
screen is: 

1. Q-RPT 

designator. 

2. 

Type of range. DF for the Q-RPT’s default range; AR for a range 
created by AutoRange. 

3. 

Q-RPT position designator.  

4. 

Current pressure unit of measure. 

5.  Full scale pressure in current unit of measure in gauge (<g>) and/or 

absolute (<a>) measurement mode.