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Because the ohmic measurement system is set up to measure two PRTs, there are two reference
resistors in the molbloc simulator. Their resistance is not identical so there are actually two reference
temperatures printed on the molbloc simulator and an average temperature which correspond to the
three temperatures on the molbox RFM [P&T] temperature display (see Section 3.4.5).
OPERATION
To verify the molbox RFM ohmic measurement system proceed as follows:
Connect a molbloc simulator P/N 401232 to the molbox RFM and initialize it as if connecting a
molbloc (see Section 2.3.3).
Press [P&T] and then [+/-] to display the molbox RFM temperature measurement.
Compare the three molbox RFM temperature measurements (upstream, downstream and average)
to the calculated reference temperature values written on the molbloc simulator.
If all disagreements between molbox RFM indications and corresponding calculated reference
temperatures are less than 0.05 °C, the ohmic measurement system verification passed.
If any disagreement between a molbox RFM indication and the corresponding calculated reference
temperature is greater than 0.05 °C, the ohmic measurement system verification failed.
Possible reasons for failure include:
•
Faulty molbox RFM internal reference resistor(s)
•
Faulty molbox RFM internal relays
•
Faulty connections between molbox RFM and the molbloc simulator
•
Faulty molbloc simulator
Check the molbox RFM to molbloc simulator connections and repeat the verification. If the out-of-
tolerance condition persists, the molbox RFM and/or the molbloc simulator need service.
Pressing [SPECIAL] and selecting <4Cal>, <2StdRes> provides access to view and edit the value of
molbox RFM's two standard resistors. Altering these values can cause out of tolerance flow readings.
In normal circumstances, these values are only altered by the factory when a reference resistor is
replaced and they should not be altered by the user.
5.4
RELOADING EMBEDDED SOFTWARE INTO molbox RFM
FLASH MEMORY
molbox RFM uses FLASH memory. This allows the embedded software that controls molbox RFM
operations and functions to be loaded into molbox RFM over its COM1 port from a personal computer
with a simple FLASH loading utility.
To replace corrupted software or upgrade to a new version, your DHI Authorized Service Provider can
provide a FLASH memory loading utility along with a file containing the molbox RFM embedded software.
These are also available for download from DHI's worldwide web site, www.dhinstruments.com.
If the embedded software you are using is suspected of a problem, record all symptoms and contact your
DHI Authorized Service Provider.
5. MAINTENANCE, ADJUSTMENTS AND CALIBRATION
Page 143
© 1998-2007 DH Instruments, a Fluke Company
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