Aalborg DFM Digital - Manual (Page 35)

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analog output calibration only), an insulated (plastic) screwdriver, a flow regulator
(for example - metering needle valve) installed upstream from the Mass Flow
Meter and a pressure regulated source of dry filtered nitrogen gas (or other suit-
able reference gas). It is recommended to use Aalborg
7 supplied calibration and
maintenance software to simplify the calibration process. Gas and ambient tem-
perature, as well as inlet and outlet pressure conditions should be set up in accor-
dance with actual operating conditions.
7.2 Gas Flow Calibration of DFM Mass Flow Meters
All adjustments in this section are made from the outside of the meter
via digital communication interface between a PC (terminal) and DFM.
There is no need to disassemble any part of the instrument or
perform internal PCB component (potentiometers) adjustment.
DFM Mass Flow Meters may be field recalibrated/checked for the same range they
were originally factory calibrated for. When linearity adjustment is needed, or flow
range changes are being made proceed to step 7.2.3. Flow range changes may
require a different Restrictor Flow Element (RFE). Consult your distributor or
Aalborg
7 for more information.
7.2.1 Connections and Initial Warm Up
Power up the Mass Flow Meter for at least 30 minutes prior to commencing the
calibration procedure. Establish digital RS-485/RS-232 communication between
PC (communication terminal) and the DFM. Start Aalborg
7 supplied calibration
and maintenance software on the PC.
7.2.2 ZERO Check/Adjustment
Check SENSOR AVERAGE counts on the DFM LCD status line. Keep pressing the
(
p) [Up] button from the main screen until status line will display Device Sensor
Average ADC counts. With no flow conditions the sensor Average reading must be
in the range 120 10 counts. If it is not, perform Auto Zero procedure (see sec-
tion 5.3.10 "Zero Calibration").
7.2.3 Gas Linearization Table Adjustment
Note: Your DFM Digital Mass Flow Meter was calibrated at the
factory for the specified gas and full scale flow range (see device
front label). There is no need to adjust the gas linearization table
unless linearity adjustment is needed, flow range has to be changed,
or new additional calibration is required.
Any alteration of the gas linearization table will void calibration
warranty supplied with instrument!
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