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5.4.1
OHMIC Measurement System Calibration/Adjustment
Procedure
The molbox1+ channels are calibrated individually. The standard calibration procedure
requires at least two simulators and is performed as follows:
With Channel A selected, press [SPECIAL], <4cal>, <2temp> to read and record the
current values of TA and TM for Channel A, then exit to the main run screen to select
Channel B and repeat the process to read and record the current values of TA and TM
for Channel B.
With Channel A selected, the [P&T] button twice to display the real time temperature
readings.
Connect a molbloc simulator to the molbox1+ Channel A and initialize it as if connecting a
molbloc (see Section 3.5.1).
Enter the average molbloc simulator calibrated temperature and the molbox1+ top row
centered calibration temperature reading (the averaged temperature) for each
temperature point into a spreadsheet. Repeat steps and for each simulator.
Calculate the "non-corrected" temperature readings by backing out the as received TA
and TM recorded in Step above, following:
non-corrected reading = (corrected reading - TA)/TM
Perform a best fit linear regression to find the offset and slope that best fit the non-
corrected temperature readings to the calibrated molbloc simulator temperatures. Most
commercial spreadsheet products have a standard function to perform a linear
regression. The offset, in the current temperature unit, is the new value of TA, the slope
is the new value of TM.
Press [SPECIAL], <4cal>, <2temp> to write the new values of TA (in the current unit of
measure) and TM and the new calibration date (YYYYMMDD) for the channel that is
being calibrated.
Calculate "as left data" for the calibration:
as left reading = (non-corrected reading • new TM) + new TA
If desired, verify the as left data by rerunning the calibration with the new TA and TM
applied and checking that the disagreements between the molbloc simulators and the
molbox1+ temperature readings are in tolerance.
Repeat steps thru for Channel B.
•
The value of TA must be entered in the current unit of measure, either °C
or °F, that is displayed by the molbox1+.
•
If you are not familiar or comfortable with the mathematics used for TA
and TM manipulation, it is recommended you verify the as left readings as
suggested in Step above to provide practical confirmation of the
integrity of the calculations.
•
If an out-of-tolerance condition persists, the molbox1+ and/or the molbloc
simulator(s) may need service.
5. MAINTENANCE, ADJUSTMENTS AND CALIBRATION
Caution
Page 151
© 1995 - 2010 Fluke Corporation, DH Instruments Division
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