4.4
Safety interlocks and control-system
The pump protection and safety interlock features are listed below. Refer to the instruction
manual supplied with the EXC300M Controller for a full description of these features :
·
The EXC300M Controller monitors the temperature and the electrical power consumption
of the EXT250M pump. If the EXC300M Controller detects excessive power consumption or
temperature, the rotational speed of the pump motor is reduced until the power and
temperature return to normal.
·
If the rotational speed is reduced to 50% of nominal speed, then the pump is stopped
immediately (or after a user defined time delay) and the ‘Fail’ LED on the EXC300M
Controller goes on.
·
If pump rotational overspeed is detected by the EXC300M Controller, the pump is stopped
immediately and the ‘Fail’ LED on the EXC300M Controller goes on.
·
If the EXC300M Controller detects excessive displacement of the rotor assembly, then the
pump is stopped immediately and the ‘Emergency’ LED on the EXC300M Controller goes
on.
·
If there is a power failure or the electrical supply is accidentally disconnected, the EXC300M
Controller automatically switches the EXT250M to operate as a generator and shuts down
the pumping system safely. As the EXT250M decelerates, regenerative braking is used to
maintain the electrical supply to the electromagnetic bearing until a sufficiently low
rotational speed has been reached for the rotor assembly to set down safely onto the safety
bearings.
The EXC300M Controller is supplied configured to automatically stop the EXT pump if the ‘Fail’
or ‘Emergency’ LEDs go on. Isolate the pump from the backing pipeline or vent your system to
prevent the backstreaming of oil and contamination of your vacuum system. Once the EXT250M
has stopped, rectify the cause of the failure (refer to Section 5.5), press the EXC300M Controller
Start/Stop button to reset the ‘Fail’ condition, and restart the EXT250M. If the pump is hot, allow
sufficient time for it to cool before you restart it.
4.5
Emergency operation : loss of magnetic suspension
4.5.1
General
The EXT250M is designed to survive at least five full-speed touchdowns onto the safety bearings
under vacuum. We recommend that you return the EXT250M to a BOC Edwards Service Centre
after five touchdowns have occurred, or earlier if you have any doubts about the pump’s
performance (see Section 5).
24
EXT250M Turbomolecular Pump
