MKS HPS 903 Series, Руководство по эксплуатации и обслуживанию

Страница: 23 / 36

17 Cold Cathode Ionization Vacuum Sensor
Below is a table which shows the correction factors needed to obtain curves
for selected gases other than air/nitrogen. You can make your own graph from
this information or use the graph on the previous page which shows the same
information.
Table of Correction Factors
P
H
2
= P
Indicated
x 2.5
P
He
= P
Indicated
x 8
P
Ar
= P
Indicated
x 0.8 below 10
-4
P
Ar
= P
Indicated
x 0.5 at 10 -3
P
Ar
= P
Indicated
x 0.2 at 10
-2
Calibrating for Other Gases
Air calibration is indistinguishable from nitrogen. To determine the voltage/
pressure relationship for a gas which is not shown on the graph on the
previous page, you need to calibrate the (IMT). This requires a gas
independent sensor, such as a capacitance manometer or spinning rotor
gauge, to act as the calibration standard. A curve can then be generated.
The Series 903 (IMT) cannot be calibrated for direct pressure
readings of gases other than air or nitrogen. The calibration is
intended only to match the air/nitrogen curve of the sensor.
Gas-type dependence can either be an advantage or a disadvantage. On
the one hand, it's possible to use a cold cathode sensor as a leak
detector. On the other hand, the pressure indication of a gas may vary by
a factor of five or more.
Also, calibration factors, or relative sensitivity factors, for cold cathode
ionization sensors are not the same as those for hot cathode sensors.