Contamination - Instrutech Hornet User Manual

Instruction Manual IGM401 Hornet

Contamination

9.7
The most common cause of all vacuum gauge failures is contamination of the sensor. Noisy or erratic readings,
and total gauge failure are all possible indications of gauge contamination.
Contamination can be generally characterized as either a reaction of process gases with sensor elements, or an
accumulation of material on the sensor elements. Sensors that fail due to chemical reaction are generally not
repairable. Sensors that fail due to condensation, coatings, or particles may possibly be restored by performing
the degas function.
A) Reactive Gases
If process gases react with the materials of construction of the sensor, the result is corrosion and disintegration
of the sensor over time. For general vacuum applications, dual yttria coated filaments are offered for use with
air and inert gases such as N , argon, etc. Optional dual tungsten filaments are available for use with gases not
2
compatible with yttria coated filaments.
B) Oil, Condensation, Coatings, and Particles
If the failure is due to an accumulation of material in the gauge, you may be able to rid the gauge sensor of
adsorbed gas using the degas function of the device.
Oils and hydrocarbons: Exposure of the gauge internal surfaces to oils and hydrocarbons can result in sensor
contamination. Some of these types of contamination may be removed by degas. Furthermore, if there is the
possibility of oil back streaming from wet vacuum pumps, it is recommended that a filter or trap be installed to
prevent contamination of components of your vacuum system.
In some vacuum processes, desorbed and sputtered materials from the process may enter vacuum components
connected to the process vacuum chamber by line-of-sight transport especially under high vacuum conditions,
i.e., in the molecular flow regime. To prevent materials that may be transported via line-of-sight momentum
from entering your vacuum gauge or other components, it is advisable to install some form of apparatus that
o
will block the line-of-sight. In some cases a simple 90 elbow may help prevent or reduce the transport of
particles from entering your vacuum gauge.
In the event of gauge contamination you can attempt to degas the sensor. If degas fails to resolve the issue,
switch to second filament or replace the sensor as described in the next section.
InstruTech, Inc.
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