The Sensor breaks down into three subassemblies: the backshell, internal, and the body subassemblies. Only the internal and body subassemblies are exposed to vacuum.
To disassemble the Sensor, remove the backshell subassembly as follows (Steps 1 through 4 are not necessary when replacing internal parts):
If ultrasonic cleaning, 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.
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 degrees C) for one minute. Follow with a preliminary rinse of deionized water. Remove smut (the black residue left on aluminum parts) 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.
Do not damage the leaf spring while cleaning the Sensor.
Each of the above cleaning methods should be followed with multiple rinses of deionized water. Dry all internal components and the sensor body in a clean oven. The two ceramic spacers are slightly porous and will require longer drying time in the oven to drive off the absorbed water.
To reassemble, reverse the order used during disassembly. Note the following special tightening procedure of the guard bolt. The bolt has a 3/8"-40 thread, which is delicate.
To prepare the Sensor for bakeout up to 125 degrees C, remove the high voltage and ion current cables only.
To prepare the Sensor for bakeout up to 250 degrees C, also remove the backshell and bulkhead subassembly shown in the diagram. Follow steps 1 through 4 of Disassembling the Series 421 Sensor (above).