Refrigeration – Low pressure cold trap process and apparatus
Reexamination Certificate
2000-07-28
2001-12-11
Capossela, Ronald (Department: 3744)
Refrigeration
Low pressure cold trap process and apparatus
C417S901000
Reexamination Certificate
active
06327863
ABSTRACT:
BACKGROUND
Cryopumps are often employed to evacuate gases within process chambers. Typically, a cryopump is coupled to a process chamber by a conduit extending therebetween with a gate valve positioned within the conduit for enabling the cryopump to be isolated from the process chamber. One common situation in which the gate valve is closed to isolate the cryopump from the process chamber is to prevent particular gases or substances introduced into the process chamber from contaminating the cryopump. Another common situation in which the gate valve is closed is during regeneration of the cryopump where the cryopumping surfaces of the cryopump are warmed to release the gases trapped thereon, including hydrogen gas. Failure to close the gate valve during regeneration may allow the released hydrogen gas to enter the process chamber from the cryopump, thereby subjecting the hydrogen gas to the possibility of ignition.
The gate valves in some systems are controlled by a control system which has an interlock for locking the gate valve in particular situations, for example, during regeneration of the cryopump, during power outages, when high levels of particular gases or substances are within the process chamber, etc. Usually, the locked gate valves may be reopened by changing operating modes of the cryopump, or by using reset or override switches. Consequently, such gate valves may be opened during potentially dangerous or unsafe conditions, for example, when hydrogen gas is present within the cryopump. Opening of a gate valve with hydrogen gas present in the cryopump may result in an explosion or fire if the hydrogen gas flows into the process chamber and ignites.
SUMMARY
The present invention provides a cryopump coupled to a gate valve and an electronic controller therefor, where the gate valve is prevented from being opened during unsafe conditions, for example, when combustible gases such as hydrogen may be present in the cryopump, but may be operated during safe conditions when combustible gases are not present. A method of controlling the gate valve includes automatically determining with a controller whether the cryopump is operating in one of safe and unsafe conditions. The unsafe conditions include situations where combustible gas may be present in the cryopump. The safe and unsafe conditions are correlated to parameters of the cryopump including operational modes of the cryopump, and sensed parameters. The gate valve is automatically controlled with the controller based on the determination of safe and unsafe conditions. The gate valve is automatically locked closed during unsafe conditions and remains locked until the unsafe conditions are removed. The gate valve is automatically unlocked after the unsafe conditions change to safe conditions. During safe conditions, the gate valve is freely operable.
In preferred embodiments, such control of the gate valve is accomplished locally wherein the controller is integral with the cryopump. This allows the controller to override other systems controlling the gate valve, for example the overall process system. Consequently, even if the process system specifies that the gate valve is to be opened, the controller will keep the gate valve locked closed if an unsafe condition is present.
During regeneration of the cryopump, purge gas is applied through the cryopump for purging gases, including combustible gases, from the cryopump. An initial predetermined time period is timed with a timer at the start of purging. The controller automatically determines during the initial predetermined time period that the cryopump is in an unsafe condition. If regeneration of the cryopump is aborted during the initial predetermined time period of purging, the controller automatically determines that an unsafe condition continues to exist. Once aborted, if regeneration of the cryopump is restarted and purge gas is applied again for more than the initial predetermined time period, the controller automatically determines that the unsafe condition has changed to a safe condition.
During regeneration, if a sensor in the cryopump senses that a purge gas failure has occurred during the initial predetermined time period, the controller automatically determines that an unsafe condition continues to exist. Once a purge gas failure has occurred, if regeneration is aborted, the purge gas failure remedied, regeneration restarted, and purge gas applied through the cryopump for more than the initial predetermined time period, the controller will automatically determine that the unsafe condition has changed to a safe condition. The initial predetermined time period is at least about 1½ minutes but is preferably about 5 minutes.
If a pumping surface of the cryopump rises in temperature from below 20 K, preferably 18 K, to above 20 K, preferably 22 K, as sensed with a sensor in the cryopump, the controller automatically determines that an unsafe condition exists. If the sensor senses that the temperature then drops back below 20 K, preferably below 18K, the controller automatically determines that the unsafe condition has changed to a safe condition. If the pumping surface remains above 20 K, preferably 22 K, and purge gas is applied through the cryopump for more than the predetermined time period, the controller will automatically determine that the unsafe condition has changed to a safe condition.
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Allen Brett W.
Geden Carl H.
Yamartino Stephen J.
Capossela Ronald
Hamilton Brook Smith & Reynolds PC
Helix Technology Corporation
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