Operation and Maintenance Manual Model 7AA Wafer Grinder
9 - 8 Version 1.2 - April 18, 1996
By noting the typical maximum vacuum level measured with the
gauge the switch should trip at some level below this point to
avoid nuisance vacuum errors. Conversely, setting the vacuum
level too low may cause handling problems. Typical vacuum
levels are approximately 15" HG; typical switch settings are
approximately 8" HG. This ensures sufficient vacuum for
dependable wafer transfer without nuisance vacuum errors. By
opening and closing the needle valve the vacuum level can be
adjusted to measure the switch setting.
To test the status of the vacuum switch connect a DC voltmeter
across the two switch leads (the positive lead should be
connected to wire 21). When the switch is closed the voltage
will be zero; when the switch is open the voltage will be +24
volts. On newer machines a terminal strip adjacent to the
vacuum switch manifold provides led indication of vacuum and
pressure switch status. The led is illuminated when the vacuum
switch is closed (on).
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