Edwards, nEXT Turbomolecular Pumps, nEXT240, nEXT300 and ...

B800-00-880 Issue B
CAUTION
Do not open a manual vent valve until the pump rotational speed has fallen below 50%, otherwise the rate of
pressure rise may be too high, which could damage the pump. In an emergency only, open the vent-valve quickly
to decelerate the pump rotor in the shortest possible time.
Note:
If you are using the Controller to control a TAV solenoid valve, there is a 2-second delay between either a
Stop command being received or a fault condition being detected and the vent valve opening. This delay
allows time for gauges, valves and other equipment to be switched off before venting occurs.
Operation
The green indicator LED on the Controller will extinguish as rotational speed drops below Normal speed. At very low
speeds you will see the yellow indicator LED flashing – it will extinguish when the pump has stopped.
4.9 Operation at extreme conditions
4.9.1 Operation with high inlet pressure
If the nEXT pump inlet pressure rises, the power supplied to the pump-motor will increase to counteract the gas
frictional load. The pump rotational speed will remain constant until the peak power level is reached; beyond this
level, the speed of the pump will start to reduce.
If the pump speed falls to below 50% of full rotational speed, the Timer will start if it is enabled. If the speed does
not recover to above 50% speed before the timeout period expires, the pump will shut down and display a Fail signal.
If the Timer is disabled, the pump will immediately shutdown and display a Fail signal if the speed drops below 50%
of full rotational speed. Refer to Section 2.7 for the maximum power delivered to the pump and to Table 6, for
maximum allowable inlet pressure.
4.9.2 Operation at high temperatures
Temperature sensors within the pump mechanism and electronics are monitored by an internal system. If the system
detects that any internal temperatures are too high, the power supplied to the pump-motor is reduced; the pump
may not therefore be able to maintain full rotational speed if it is too hot.
If the pump speed falls to below 50% of full rotational speed, the Timer will start if it is enabled. If the speed does
not recover to above 50% speed before the timeout period expires, the pump will shut down and display a Fail signal.
If the Timer is disabled, the pump will immediately shutdown and display a Fail signal if the speed drops below 50%
of full rotational speed. Refer to Section 2.11 for pump operating ranges and Section 3.10 for advice on pumpcooling.
4.9.3 Protection against over-speed
Control software within the Controller regulates the pump rotational speed and prevents the pump operating above
its normal full rotational speed. In the unlikely event of a failure of this control software, the Controller has a builtin
safety circuit that checks whether the pump is running at over-speed. If an over-speed condition is detected, the
Controller automatically shuts down power to the pump-motor and slows it down to rest. The Controller will signal
a Fail condition if over-speed has been detected.
If you suspect that your pump may be running at over-speed you should switch it off and consult Edwards or your
supplier.
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