How To Zero the Flow Controller
Chapter Four: Operation
40
How To Zero the Flow Controller
Ensure that no gas flow is entering the flow controller.
1. Apply gas, at a regulated pressure, to the flow controller.
2. If your system includes a positive shutoff valve, located either upstream or downstream
of the instrument, close it.
3. For an MFC: Command the control valve open by sending a full scale set point (5
VDC) signal, or:
15-pin Type “D” connector: Connect pin 4 (valve open) to pin 11 or 12 (signal ground).
9-pin Type “D” connector: 5 Volts to pin 1 (to open the valve).
Edge Card connector: Connect pin D (valve open) to pins 10, B, or C (signal ground).
A positive flow may occur momentarily while the gas pressure equalizes across the flow
controller.
Note
A set point command signal greater than 50 mV (1% of full scale) is
required for the flow controller to generate an output.
For an MFM: Skip to step 2 in Adjust the Zero Pot
Adjust the Zero Pot
1. For an MFC: Once flow through the controller has stopped (reached zero flow), remove
the set point or valve open command.
2. Turn the Zero pot (located on the inlet side of the flow controller) until the readout
displays zero.
Refer to Figure 1, page 27, for the location of the Zero pot.
If you are using an MKS power supply/readout unit, the flow controller can also be
zeroed at the front panel of the readout unit.
Note
A DeviceNet
MFC/MFM does not have a zero pot, use the zero offset
command instead.
3. Open the positive shutoff valve.
An MFC may indicate a small, positive flow (<1.0% 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.
