MKS HPS 903 Series, Operation And Maintenance Manual

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19 Cold Cathode Ionization Vacuum Sensor
Contamination of the (IMT) Sensor
If pressure readings appear to be erratic, the sensor tube may be
contaminated. Inspect it visually. If contamination is visible, you should
replace the internal components with an Internal Rebuild Kit or a Rebuild
Sensor (see Accessories, p. 22).
Depending on the degree of contamination and application of the (IMT), the
internal parts may be cleaned — either ultrasonically, with mild abrasives,
or chemically.
For the remaining sections, please refer to the figure shown on
page 21.
Disassembly
Tools required: Phillips head screwdriver; clean tweezers; clean, smooth-jaw,
needle-nose pliers
1) Remove the two Phillips head screws holding the electronics assembly to
the sensor body. Remove the electronics assembly.
2) Using the smooth-jaw, needle-nose pliers, firmly grab the compression
spring at the tip closest to the flange.
3) Pull on the compression spring while rotating it to free it from the formed
groove of the sensor body . Continue to pull until the compression
spring is completely free.
4) Carefully remove the remaining components from the sensor body.
Do not bend the anode or the leaf spring on the ion current
feed through pin when assembling or disassembling the
sensor.
Cleaning
If cleaning ultrasonically, use high quality detergents compatible with
aluminum, such as ALCONOX
®
.
Scrubbing with mild abrasives can remove most contamination.
Scotch-Brite™ or a fine emery cloth may be effective. Rinse with alcohol to
remove particulates.
Clean aluminum and ceramic parts chemically in a wash, such as a 5 to
20% sodium hydroxide solution (not for semiconductor processing), at room
temperature (20°C) for one minute. Follow with a preliminary rinse of
deionized water. Remove smut (the black residue left on aluminum parts due
to this process) in a 50 to 70% nitric acid dip for about 5 minutes.
Chemical cleaning should not be used to clean the anode; mild
abrasives or ultrasonic cleaning are acceptable.
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