Specifications

5. MAINTENANCE, ADJUSTMENTS AND CALIBRATION
Page 141 © 1998-2007 DH Instruments, a Fluke Company
The value of PA is always in Pascal [Pa]. The value of PM is dimensionless.
5.2.5 RPT CALIBRATION/ADJUSTMENT PROCEDURE
WITHOUT USING CALTOOL FOR RPTS SOFTWARE
Most users should use CalTool for RPTs software to assist in the calibration of molbox
RFM reference pressure transducers. CalTool for RPTs and its documentation are
provided on the General Accessories Disk delivered with molbox RFM. Whether using
CalTool or not, before proceeding to calibrate molbox RFM RPTs, Sections
5.2.1 through
5.2.5 of this manual should be reviewed thoroughly.
The standard molbox RFM RPT calibration procedure is:
n Determine the RPT(s) to be calibrated (upstream and downstream, or microrange
if present). The upstream and downstream absolute RPTs are calibrated simultaneously.
o Set-up and prepare the molbox RFM for calibration of the selected RPT(s)
(see Sections 5.2.2 and 5.2.3).
p Press [SPECIAL] and select <4cal>, <1pressure>, <1upstrm, 2dnstrm or 3micro>,
<2v
iew> to read and record the current values of PA and PM for the RPT(s) to be
calibrated (see Section 5.2.4.2).
q Press [SPECIAL] and select <4cal>, <1pressure>, <1upstrm, 2dnstrm or 3micro>,
<1run> to display the real time pressure readings of the RPT(s) to be
calibrated
(see Section 5.2.4.1).
r Apply
the calibration pressures (generally 20 % increments ascending and descending)
for the RPT(s) recording the pressure applied by the standard and the molbox RFM
RPT(s) reading(s) at each calibration point.
The standard calibration range for the upstream and downstream absolute RPTs is
70 to 550 kPa absolute (10 to 80 psia). The standard calibration range for the
microrange differential RPT is 0 to 12.5 kPa (0 to 1.8 psi). Dwell at least 30 seconds
after setting the reference pressure at each point to allow full stabilization. The data
recorded is the "as received" data for this calibration.
s Enter the calibration pressure and RPT reading for each point into a spreadsheet.
Calculate the "non-corrected" RPT readings by backing out the as received PA and PM
recorded in Step p above, following:
non-corrected reading = (corrected reading - PA)/PM
t Perform a best fit linear regression to find the offset and slope that best fit the non-
corrected RPT readings to the calibration standard pressures. Most commercial
spreadsheet products have a standard function to perform a linear regression. The
offset, in Pascal [Pa], is the new value of PA, the slope is the new value of PM.
u Press [SPECIAL] and select <4cal>, <1pressure>, <1upstrm, 2dnstrm or 3micro>,
<3edit> to write the new values of PA (always in Pascal) and PM and the new calibration
date (YYYYMMDD) for the RPT(s) that is (are) being calibrated (see Section
5.2.4.2).
v Calculate “as left data" for the calibration:
as left reading = (non-corrected reading • new
PM) + new PA
w If desired, verify the as left data by rerunning the calibration with the new PA(s) and
PM(s) applied and checking that the disagreements between the calibration standard and
the RPT readings are in tolerance.