MKS HPS 945 Series, Operation And Maintenance Manual

Page: 27 / 38

21
Digital Pirani vacuum Sensor System
The nitrogen equivalent pressures of some gases can exceed
the measuring capabilities of the Series 945 Pirani Controller.
For example, a true pressure of 6.0 Torr of helium is equivalent
to a
nitrogen equivalent pressure of several 1000 Torr. The
Series 945 Pirani Controller is not capable of measuring this
pressure of helium.
Calibrating for Other Gases
To determine the voltage/pressure relationship for gases which are not shown
in the graph or table, you need to calibrate the Series 945 Pirani System with
this gas. This calibration requires a gas-independent sensor, such as a
capacitance manometer, to act as a standard. A curve like that of page 16
can then be generated and used as described above.
The Series 945 Pirani Controller is not intended to 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 Controller to the characteristic of a particular sensor.