Chapter Four: Operation in Normal Mode
How To Span a Sensor with a Reference
115
How To Span a Sensor with a Reference
This procedure stores a span constant for a spanned gauge. This makes the upper pressure
reading of the spanned gauge agree with the pressure reading of the referenced gauge. Spanning
is done with two sensors that are well within their measurement ranges.
Note
This procedure does not apply to capacitance manometers.
Spanning adjusts the slope of a gauge's
Pressure versus Actual Pressure (or other
measured parameter) line.
P
r
e
s
s
u
r
e
R
e
a
d
i
n
g
Reference Point
New slope
Original slope
Actual Pressure (or other measured parameter)
Figure 30: Spanning a Sensor with a Reference
Note
1. Pirani gauges must be reading above 100 Torr, and the reference
channel must be within a decade of the Pirani channel for a valid span.
2. When spanning a Pirani gauge, the reference sensor can be anything
except an ion gauge. This includes another Pirani.
3. For a successful span of an ion gauge, the reference must be a
capacitance manometer. The capacitance manometer must be at least
a decade above its zero, reading within one decade (
±
) of the
unspanned ion gauge, and reading at or below 10 mTorr.
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