Re: FEG filament

On 1 Jan 2007 02:43:22 -0800, mp76ers@xxxxxxxxx wrote:

We have a Philips CM-200 FEG TEM. We have a problem with our FEG
filament.At start (Extaction Voltage=2.2 kV) its emission is about 30uA
but at operating mode(EXt=3.8kV)its emission goes down ,and while
working its emission drops to 1.2uA gradually. Aftrer closing V7 valve
its emission increases.
At first we think its filament is over,but we didn't observe such a
behaviour with one befor this Gun.
we want to know whether the gun life is over or is there any other
problem?

I'm not familiar with the CM-200. What is V7? If this is an
isolation valve for the gun chamber, it ought to be closed all the
time I would think. If it is column isolation valve, then the problem
is still what I suspect....degraded vacuum in the gun chamber.

Can you get a readout of gun chamber vacuum and main/column vacuum?
If so, what are they?

If vacuum deteriorates, then likely suspect is a bad ion pump or its
power supply.

Iext is a key variable for the FE guns. If the gun gets poisoned by
poor vacuum, you can either bake out the gun chamber or replace the
gun. What brand of gun is used? Probably FEI.

gg



Kiss French. Drink California.
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