Omega FMA 4000 User Manual page 26

Gas flow calibration parameters are separately stored in the Gas Dependent por-
tion of the EEPROM memory for each of 10 calibration tables. See APPENDIX I
for complete list of gas dependent variables.
Note: Make sure the correct gas number and name selected are
current. All adjustments made to the gas linearization table will be
applied to the currently selected gas. Use Gas Select command via
digital communication interface (see paragraph 8.3 ASCII Command
Set "FMA 4000 SOFTWARE INTERFACE COMMANDS") or Omega
supplied calibration and maintenance software to verify current gas
table or select a new gas table.
The FMA 4000 gas flow calibration involves building a table of the actual flow val-
ues (indexes 114, 116, 118, 120, 122, 124, 126, 128, 130, 132, 134) and corre-
sponding sensor readings (indexes 113, 115, 117, 118, 119, 121, 123, 125, 127,
129, 131, 133).
Actual flow values are entered in normalized fraction format: 100.000 % F.S. cor-
responds to 1.000000 flow value and 0.000 % F.S. corresponds to 0.000000 flow
value. The valid range for flow values is from 0.000000 to 1.000000 (note: FMA
4000 will accept up to 6 digits after decimal point).
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.).
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.
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
FMA 4000. If the difference between calibrator and FMA 4000 flow reading is
more than 0.5% F.S., make a correction in the sensor reading in the correspon-
ding position of the linearization table (see Index 133).
If the FMA 4000 flow reading is more than the calibrator reading, the number of
counts in the index 133 must be decreased. If the FMA 4000 flow reading is less
than the calibrator reading, the number of counts in the index 133 must be
increased. Once Index 133 is adjusted with a new value, check the FMA 4000 flow
rate against the calibrator and, if required, perform additional adjustments for
Index 133.
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