Chapter Four: Operation in Normal Mode
How To Zero a Sensor/MFC
109
Note
1.
Before zeroing an MFC, verify that there is no gas flow through the
unit. Two ways to accomplish this involve an upstream valve, or
with a digital override (refer to How To Command an MFC Close
Override, page 121).
2.
To zero an MFC, the MFC reading must be close to 0.0. The 146
unit will not perform the zero function if the reading deviates from
0.0 by more than ±10% of the full scale range of the MFC. For
example, to zero a 10 sccm unit, the reading must be 0.0 ±1.0 sccm.
1. Pump the gauge down to a pressure below the resolution of the gauge (<0.5 mTorr for a
TC gauge). For an MFC, ensure that no gas is flowing through the unit.
2. Repeatedly press the [
DISPLAY MODE
] key until the 146 unit is in Normal Mode.
The system responds by scrolling through modes.
3. Press the [
ZERO
/
EXP
] key, followed by [1], [2], [3], or [4].
The system responds by zeroing the sensor/MFC of the channel number pressed. The
reading in the selected channel’s display goes to zero.
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