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B) Oil, Condensation, Coatings, and Particles
If the failure is due to an accumulation of material in the gauge,
we may be able to restore your gauge or module by cleaning.
Contamination may be as simple as condensed water, or as
difficult as solid particles.
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
cleaning the gauge. If there is the possibility of oil back stream-
ing from wet vacuum pumps, it is recommended that a filter or
trap be installed to prevent contamination of components of your
vacuum system.
Condensation: Some gases (such as water vapor) can con-
dense on sensor surfaces, forming a liquid coating that changes
the rate at which heat is removed from the sensor (which chang-
es the calibration). The sensor can often be restored simply by
pumping on the gauge between process cycles. A dry N
2
purge
will help speed up drying, or the gauge may be gently heated
provided temperature doesn't exceed the specified limit of 40 °C,
operating.
Coatings: Some gases can condense on sensor surfaces, form-
ing a solid coating, which changes the rate at which heat is re-
moved from the sensor. Some of these coatings may be re-
moved by cleaning the gauge.
Particles: Particles generated by the process may enter the
gauge during the process cycle or during the venting cycle. The
result is interference with heat removal from the sensor. In this
case, cleaning may be able to remove particles from the gauge.
However, particulate contamination is the most difficult to re-
move as particles can become stubbornly trapped inside the
gauge. In some processes, solid particles are created during the
process throughout the chamber including inside the gauge. Par-
ticles tend to form on cooler surfaces such as in a gauge at room
temperature. You may slow down the build-up of particles in the
gauge by keeping the gauge warm (within specified limits) during
the process cycle.
Summary of Contents for PGE500
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