Aalborg XFM Digital - Manual (Page 28)

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Sensor readings are entered in counts of 12 bits ADC output and should always
be in the range of 0 to 4095. There are 11 elements in the table so the data should
be obtained at an increment of 10.0 % of full scale (0.0, 10.0, 20.0, 30.0, 40.0,
50.0, 60.0, 70.0, 80.0, 90.0 and 100.0 % F.S.).
If a new gas table is going to be created, it is recommended to start calibration
from 100% full scale. If only linearity adjustment is required, calibration can be
started in any intermediate portion of the gas table.
Using the flow regulator, adjust the flow rate to 100% of full scale flow. Check the
flow rate indicated against the flow calibrator. Observe the flow reading on the
XFM. If the difference between calibrator and XFM flow reading is more than 0.5%
F.S., make a correction in the sensor reading in the corresponding position of the
linearization table (see Index 133).
If the XFM flow reading is more than the calibrator reading, the number of counts
in the index 133 must be decreased. If the XFM flow reading is less than the cal-
ibrator reading, the number of counts in the index 133 must be increased. Once
Index 133 is adjusted with a new value, check the XFM flow rate against the cal-
ibrator and, if required, perform additional adjustments for Index 133.
If a simple communication terminal is used for communication with the XFM, then
“MW” (Memory Write) command from the software interface commands set may
be used to adjust sensor value in the linearization table (see section 8.3 for com-
plete software interface commands list).
Memory Read “MR” command can be used to read the current value of the index.
Assuming the XFM is configured with RS-485 interface and has address “11”, the
following example will first read the existing value of Index 133 and then write a
new adjusted value:
!11,MR,133[CR] - reads EEPROM address 133
!11,MW,133,3450[CR] - writes new sensor value (3450 counts) in to the index 133
Once 100% F.S. calibration is completed, the user can proceed with calibration for
another 9 points of the linearization table by using the same approach.
Note: It is recommended to use Aalborg® supplied calibration and
maintenance software for gas table calibration. This software includes
an automated calibration procedure which may radically simplify
reading and writing for the EEPROM linearization table.
Note: Do not alter memory index 113 (must be 120 counts) and 114
(must be 0.0). These numbers represent zero flow calibration points
and should not be changed.