Chapter Four: Operation How To Zero the Integral Mass Flow Meter
35
How To Zero the Integral Mass Flow Meter
Ensure that no gas flow is entering the 649 controller.
1. Apply gas, at a regulated pressure, to the 649 controller.
2. Close the positive shutoff valve downstream of the instrument.
3. Command the control valve open by connecting the valve open pin to signal ground.
On the Type “D” connector, connect pin 4 (valve open) to pin 11 or 12 (signal ground).
A positive flow may occur momentarily while the gas pressure equalizes across the 649
controller.
Adjust the Zero
1. Once flow through the controller has stopped (reached zero flow), remove the valve open
command.
2. Turn the
ZERO pot (located on the side of the controller) until the readout displays zero.
Refer to Figure 3, page 15, for the location of the
ZERO pot.
3. Open the positive shutoff valve.
The controller may indicate a small, positive flow (<2.0% F.S.) due to a leak through its
control valve. However, do
not “zero out” this flow since it represents an actual flow
measurement inherent in the system.
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