Aalborg GFC - Manual (Page 14)

5.2 Flow Signal Output Readings
The flow signal output can be viewed on the LCD display, remote panel meter, dig-
ital multimeter, or other display device connected as shown in Figure 2.1.
If an LCD display has been ordered with the GFC, the observed reading is in
direct engineering units, for example, 0 to 10 sccm or 0 to 100 slpm (0 to 100%
indication is optional). Engineering units for a specific GFC are shown on the flow
transducer's front label.
Analog output flow signals of 0 to 5 VDC and 4 to 20 mA are available at the
appropriate pins of the 15-pin “D” connector at the side of the GFC transducer
(see Figure 2-1).
Meter signal output is linearly proportional to the mass molecular flow rate of the
gas being metered. The full scale range and gas for which your meter has been
calibrated are shown on the flow transducer's front label.
Default calibration is performed for 0 to 5 VDC input/output signal. If 4-20 mA out-
put signal is used for flow indication on the GFC, which was calibrated against 0
to 5 VDC input signal, the accuracy of the actual flow rate will be in the specified
range (+1.5%) of full scale, but the total of the output 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.
For optional RS232 or IEEE488 interfaces please contact your distributor or Aalborg
7.
5.3 Swamping Condition
If a flow of more than 10% above the maximum flow rate of the Mass Flow
Controller is taking place, a temporary condition known as “swamping” may occur.
Readings of a “swamped” meter cannot be assumed to be either accurate or lin-
ear. Flow must be restored to below 110% of maximum meter range. Once flow
rates are lowered to within calibrated range, the swamping condition will end.
Operation of the meter above 110% of maximum calibrated flow may increase
recovery time.
5.4 Setpoint Reference Signal
GFC flow controllers have built-in solenoid valves (GFC 17/37/47) or motorized
valves (GFC 57/67/77), and allow the user to set the flow to any desired flow rate
within the range of the particular model installed. The solenoid valve is normally
closed (NC) when no power is applied.
The motorized valve can be in any position depending on the operation mode of
the GFC during disconnecting of the power. For example if the motorized valve
was left in the OPEN purge position after disconnecting power from the GFC it will
be in the OPEN position. It is the customers responsibility to provide a solution to
shut down the flow in case of a power outage. When power is applied to GFC 57
/67/77 models, the valve automatically closes within the first ten seconds regard-
less of the set point and valve override signals.
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