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Entry  Sat Apr 25 00:45:31 2009, Yoichi, Configuration, VAC, Reflector for the cryopump temperature monitor changed 
    Reply  Sat Apr 25 02:54:25 2009, Yoichi, Configuration, VAC, Reflector for the cryopump temperature monitor changed 
Message ID: 1520     Entry time: Sat Apr 25 00:45:31 2009     Reply to this: 1521
Author: Yoichi 
Type: Configuration 
Category: VAC 
Subject: Reflector for the cryopump temperature monitor changed 
The temperature of the cryopump head is monitored by a photo switch looking at an aluminum foil reflector attached to the needle of the temperature gauge.
If the needle moves out of the 14K position, the photo switch will be triggered to close the cryopump gate valve.
However, this photo switch system has been touchy.
Tonight, the switch falsely tripped several times and closed the gate valve, which caused lock losses as the motion of the valve generates a lot of vibrations.
Seems to me, it was caused by the poor/irregular reflection from the wrinkled aluminum foil on the needle.
So I replaced the aluminum foil with a brand-new shiny one.
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