Aalborg GFM - Manual (Page 13)

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5. OPERATING INSTRUCTIONS
5.1 Preparation and Warm Up
It is assumed that the Mass Flow Meter has been correctly installed and thor-
oughly leak tested as described in section 2. Make sure the flow source is OFF.
Apply power to the unit by plugging the power supply line into the DC power jack
(or 9-pin 'D' connector) on the side of the meter. Allow the Mass Flow Meter to
warm-up for a minimum of 15 minutes.
SUPPLYING DC POWER TO THE POWER JACK AND THE “D” CONNECTOR AT
THE SAME TIME WILL DAMAGE THE METER. DC POWER JACK POLARITY
IS CENTER POSITIVE.
During initial powering of the GFM transducer, the flow output signal will be indi-
cating a higher than usual output. This is indication that the GFM transducer has
not yet attained it's minimum operating temperature. This condition will automat-
ically cancel within a few minutes and the transducer should eventually zero. If
after the 15 minutes warm-up period, the display still indicates a reading of less
than ± 3.0 % of F.S., readjust the ZERO potentiometer [R34] through the access
hole. Before zero adjustment it is good practice to temporarily disconnect the gas
source, to ensure that no seepage or leak occurs in to the meter.
ADJUSTING ZERO READING MORE THAN ± 3.0% F.S. FROM THE FACTORY
SETTINGS MAY AFFECT DEVICE CALIBRATION ACCURACY. IF SUCH
ADJUSTMENT IS REQUIRED IT IS RECOMMENDED TO PERFORM METER
RECALIBRATION TO PRESERVE DEVICE ACCURACY.
5.2 Flow Signal Output Readings
Initiate a controlled gas flow after warm up. The flow signal output can be viewed
either on the LCD display, remote panel meter, digital multimeter, or other display
device.
If an LCD display has been supplied with the GFM, the observed reading is in
direct engineering units (0 to 100% indication is optional).
Analog output flow signals of 0 to 5 VDC and 4 to 20 mA are attained at the appro-
priate pins of the 9-pin “D” connector (see Figure 2.a) on the side of the GFM trans-
ducer.
Meter signal output is linearly proportional to the mass molecular flow rate of the
gas being metered. By default calibration is done against 0 to 5 VDC output sig-
nal. If 4-20 mA output signal is used for flow indication on the GFM, which was
calibrated against 0 to 5 VDC, the total uncertainty of the reading may be in the
range of +2.5% of full scale. Optional calibration for 4-20 mA output signal is
available upon request at time of order. The full scale range and gas for which
your meter has been calibrated are shown on the flow transducers front label.
For optional RS232 interfaces please contact your distributor or Aalborg
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