Section 3 Operation
Analog I/O Setpoint (MFC Only)
This input allows the user to establish the MFC setpoint. Several input types
are available:
Analog I/O Flow Signal
This output is used to indicate the flow signal. A negative flow signal indicates
reverse flow through the device, but is NOT calibrated.
Several flow signal types are available:
Valve Override (MFC Only)
The Valve Override input allows the valve to be forced to its most closed state
or its most open state, regardless of setpoint. If this input is not electrically
connected, the MFC will operate according to the current values of the other
MFC inputs. If this input is held at 0 Vdc the valve will be forced to its most
closed state. If this input is held at +5 Vdc or greater (max. = 24 Vdc), the
valve will be forced to its full open state.
Zeroing the MFC
It may be desirable to re-zero the flow sensor if it is operated at its tempera
-
ture extremes or if it is positioned in an attitude other than that specified on
the customer order.
To zero the device’s sensor:
1. Allow the device to be powered on for 45 minutes so that it
achieves its operating temperature.
2. Close the downstream shutoff valve.The device should be full of
process gas with no pressure differential.
3. Wait at least 30 seconds for the flow signal to drop to zero.
4. Using the device’s Zero pushbutton, zero the device:
-
press the pushbutton until the device’s Status LED flashes red,
then release the pushbutton. A successful zeroing
operation is indicated by the Status LED being a steady green.
The zeroing operation can take up to 10 seconds to complete.
Note: Before zeroing the instrument, zero pressure differential MUST be established
across the device. If there is pressure across the instrument during the zero process, any
detected flow through the sensor will be misinterpreted as the zero flow reading. This will
result in calibration inaccuracy during normal operation.
Once zero differential pressure is established and verified, remove threaded cover to ac-
cess the zero button, press the recessed, momentary push-button (zero button) located on
the side of the device (See Figure 3-2) to start the zero function.
Setpoint Signal Type
Full Scale
Minimum Signal
Maximum Signal
0 to 5 Vdc
5 Vdc
0 V
5.5 Vdc = 110%
1 to 5 Vdc
5 Vdc
1 V
5.5 Vdc = 111%
0 to 20 mA
20 mA
0 mA
22 mA = 110%
4 to 20 mA
20 mA
4 mA
22 mA = 111%
Analog I/O Type
Full Scale
Minimum Signal
Maximum Signal
0 to 5 Vdc
5 Vdc
-0.5 V
5.5 Vdc = 110%
1 to 5 Vdc
5 Vdc
0.5 V
5.5 Vdc = 111%
0 to 20 mA
20 mA
0 mA
22 mA = 110%
4 to 20 mA
20 mA
3.8 mA
22 mA = 111%
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