Dwyer GFM4 User Manual
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Shut off the flow of gas into the Digital Mass Flow Meter. To ensure that no seepage
or leak occurs into the meter, it is good practice to temporarily disconnect the gas
source. From the Main Menu, the user would traverse the menu tree until reaching
the "Zero Calibration" menu. The following screen will appear:
Figure b-18, Zero Calibration (Start)
The user must acknowledge the warning that the Auto Zero procedure is about to
be started and there is absolutely zero flow thru the meter. Selecting YES confirms
that user has taken the necessary precautions and starts Auto Zero algorithm.
Selecting NO aborts the Auto Zero procedure.
To start Auto Zero use ( ) or ( ) button to highlight "Yes" option and press the
( ) [Enter] button. The following screen will appear:
Figure b-19, Zero Calibration (In progress)
The Auto Zero procedure normally takes 2 to 3 minutes during which Zero and
Sensor reading will be changed approximately every 4 seconds. The nominal value
for fully balanced sensor is 120 counts. If the GFM3/4's digital signal processor was
able to adjust the Sensor reading within 120 ±2 counts, then Auto Zero is
considered as successful and the screen below will appear:
Figure b-20, Zero Calibration (Completed)
If the device was unable to adjust Sensor reading to within 120 ± 2 counts, then
Auto Zero is considered as unsuccessful and user will be prompted with "Auto Zero
is Failed!" screen.
5.3.11 - Flow Conditions Settings
For GFM3/4 models, the flow reading can be displayed for standard or actual
conditions (Temperature / Pressure adjusted). Since mass flow sensors are
sensitive to changes in gas density and gas velocity, all mass flow meters indicate
flow rates with reference to a set of standard conditions. For Dwyer
®
Instruments,
Inc. standard conditions are defined as 21.1°C (70°F) and 101.3 kPa (14.7 psia).
Other manufacturers may use different values. Standard flow rate is the flow rate
the gas would be moving if the temperature and pressure were at standard
conditions. It is usually the most convenient measure of the gas flow because it
defines the heat-carrying capacity of the air. Actual (volumetric) flow rate is the true
volume flow of the gas exiting the flow meter. In some instances, actual (volumetric)
flow rate rather than standard flow rate may be of interest. To display actual
(volumetric) flow rate, the GFM4 will multiply the standard flow measurement by the
following density correction factor:
Where:
Ta = Actual gas temperature measured by the GFM3/4 in units of degrees Celsius
Pa = Actual absolute pressure measured by the GFM3/4 in units of PSI
In order to select Standard or Actual flow measurement, user would traverse the
menu tree until reaching the "Flow Conditions" menu. The following screen will
appear:
Figure b-21, Flow Condition Screen
Use (
) or (
) button to highlight desired option and press the (
) [Enter] button.
5.3.12 - LCD Backlight Energy-Saving Setting
The GFM3/4's LCD incorporates Energy-saving auto shut-off backlight feature. If
enabled, after 15 minutes of operation without user intervention, the LCD backlit
turns off. In order to turn on LCD backlight, press any key on the keypad. In order
to enable/disable Energy-saving auto shut-off backlight feature, user would
traverse the menu tree until reaching the "Back Light Timer" menu. The following
screen will appear:
Figure b-22, LCD Backlight Energy-Saving Screen
Use (
) or (
) button to highlight desired option and press the (
) [Enter] button.
5.4 - Flow, Temperature, Pressure output Signals Configuration
GFM3/4 Mass Flow Meters are equipped with calibrated 0 to 5 Vdc (0 to 10 Vdc
optional) and 4 to 20 mA output signals. The set of the jumpers (J2, J3, J4) on
the analog printed circuit board is used to switch between 0 to 5 Vdc, 0 to 10 Vdc
or 4 to 20 mA output signals (see Table VI).
Analog output signals of 0 to 5 Vdc, (0 to 10 Vdc optional) or 4 to 20 mA are
attained at the appropriate pins of the 25-pin "D" connector (see Figure b-1) on the
side of the GFM3/4 transducer.
The Actual Flow reading will not be calculated for %FS
engineering unit.
NOTICE
GFM3 models are equipped with gas flow rate output signal
only. GFM4 models in addition provide output signals for
temperature and pressure
NOTICE
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