MKS HPS 917, Operation And Maintenance Manual

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9 Pirani Vacuum Sensor System
Installing the
Series 917 Pirani System
Pirani Sensor Installation
Location
Locate the Pirani Sensor where it can measure chamber or manifold pressure.
Installing the Sensor away from pumps and gas sources gives the most
representative values. Place the Sensor where vibration is minimal.
Orientation
Operating position has no negative effect on accuracy. The Pirani Sensor
was designed to minimize convection. In a standard Pirani system, the
pressure reading of a horizontal versus a vertical sensor at atmospheric
pressure differs negligibly from the residual convection effect.
The Sensor is factory calibrated vertically with the vacuum port facing down.
Contamination
Locate and orient the Pirani Sensor to avoid contamination which might affect
the tube's element. For example, if the Sensor is installed directly above a
roughing pump in the system, oil vapor could contaminate the tube's filament
wire and cause the emissivity and the calibration to shift.
Install the Sensor with the vacuum port facing downward whenever possible
to prevent particulates and liquids falling or flowing into it. Using a screen or
porous filter at the port is helpful. Try an HPS
TM seal and centering ring
assembly with a screen (see Accessories, p. 21).
Venting to Atmosphere
The Pirani Sensor senses pressure by measuring heat loss from a fine
heated wire. Sudden venting at its port can greatly stress the Sensor
physically.
To avoid damage to the Sensor, vent the vacuum system to
atmosphere before removing it.
Vacuum Connection
Standard vacuum interfaces for the Pirani Sensor include:
KF 16 flange 8 VCR
®
-F (½") fitting
1
1
/3" CF flange Ø 15 mm x 30 mm tubing
2¾" CF flange Ø 18 mm x 30 mm tubing
1
/8" NPT-M fitting with a ½" compression seal