MKS HPS 945 Series, Operation And Maintenance Manual

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10
Digital Pirani vacuum Sensor System
Installing the
Series 945 Pirani System
Pirani Sensor Installation
Location
Locate the Pirani Sensor where it can measure chamber or manifold pressure.
Install it away from pumps and gas sources and where vibration is minimal to
give the most representative values.
Orientation
Since a Pirani Sensor is designed to minimize convection, operating position
does not affect accuracy. In a standard Pirani system, the atmospheric
pressure reading of a horizontal sensor versus a vertical one differs negligibly
due to residual convection.
The Sensor is factory calibrated vertically with the vacuum port facing down.
Contamination
Locate and orient the Pirani Sensor to avoid contamination which would affect
the tube's element. For example, if the Sensor is installed directly above a
roughing pump, oil vapor could contaminate the tube's filament wire and
cause the calibration to shift.
Install the Sensor with the vacuum port facing down whenever possible to
prevent particulates falling or liquids 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. 24).
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
2 ¾" CF flange Ø 18 mm x 30 mm tubing
1
/8" NPT-M fitting with a ½" compression seal
To fit the KF 16 port to a KF 10 port, use an HPS ® adaptive centering ring
(see Accessories, p. 24).
To fit the Sensor with the
1
/8" NPT, do not use the case for tightening. The
Sensor’s vacuum tubing has
9
/16" hex flats for tightening. Wrap a layer of
Teflon
®
tape on the threads of the tubing, in the direction of installation, to
ensure a leak-free seal.
Instead of the NPT fitting, you may opt to use the ½" O-ring compression
seal against the vacuum tubing above the thread,
but the O-ring seal cannot
be used for positive pressure applications.