Chapter Five: Operation in Leakage Mode
How To Zero a Sensor/MFC
133
How To Zero a Sensor/MFC
For pressure sensors, zeroing means adjusting the readout for the sensor. The zero point is the
pressure at which the instrument displays zero pressure. For capacitance manometers and Pirani
type gauges, the zero point is the output voltage at which zero pressure is referenced.
A TC gauge, unlike a capacitance manometer or Pirani type gauge, produces its maximum output
at zero pressure. The zero is adjusted by varying the power until a standard output voltage is
achieved.
Actual Pressure (or other measured parameter)
0
+
-
Zero should be lowered
Zero should be raised
Good Zero adjustment
Zero adjustment is an additive/subtractive
process which moves a gauge's range up
or down on the pressure axis.
P
r
e
s
s
u
r
e
R
e
a
d
o
u
t
Figure 36: Zeroing a Sensor
For mass flow controllers (MFC), the zero offset is subtracted from the MFC reading and added
to the set point output voltage. This is done to accommodate the internal PID control loop in an
MFC.
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