Author Topic: Faraday Cup stuck...Why?  (Read 1573 times)

D.

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Faraday Cup stuck...Why?
« on: April 05, 2017, 12:26:11 pm »
Hi All,

My PCD gets stuck in the blanked position. JEOL 8230. Polished it and reassembled. Worked for 2 days, then same deal. Anyone run into this before...found the reason why?

Thanks,
D.

Owen Neill

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    • Electron Microbeam Analysis Laboratory, University of Michigan
Re: Faraday Cup stuck...Why?
« Reply #1 on: April 05, 2017, 05:47:54 pm »
Sounds like you may have covered this already, but a couple of years back, we found a bur on the inside of the sleeve that the PCD shaft moves through. It was bad enough it actually gouged the shaft, and caused the PCD to bind up on occasion.

Also, is the N2 supply working? Bad valve, maybe? If you've started going through N2 really quickly, there might be a leak somewhere.

Good luck,
OKN

D.

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Re: Faraday Cup stuck...Why?
« Reply #2 on: April 06, 2017, 12:01:39 am »
Hi Owen,

The N2 pressure is stable. Supply seems at an acceptable rate.

We didn't see an obvious burr when we cleaned it, but it seems like the likely culprit. I'll take another look when we strip the column again, and post back what we find.  Thank you for the suggestions!

D.

D.

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Re: Faraday Cup stuck...Why?
« Reply #3 on: June 20, 2017, 02:41:50 am »
UPDATE: After a couple more attempts we seem to have sorted it out. It's been 2 months now without recurrence of the problem. We noticed that the piston, which drives the cup sensor, was VERY slightly off-center. Apparently the housing/sleeve that the piston moves through, was accidentally rotated during a previous service. The piston was thus forced to move slightly off-center. Looks like it contacted the cup at a slight angle, causing a spring to stick and not allow the cup to move as required. The rotation apparently happened a year ago, so why this only became a problem now, mystifies me.

But apparently the spring sticking happened on at least one other instrument; in that case they bent the spring in a specific manner until it started working again.

Deon.

D.

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Re: Faraday Cup stuck...Why?
« Reply #4 on: April 18, 2018, 01:11:37 am »
UPDATE 2018: After almost exactly a year, the problem has recurred (strangely, again after the annual service). Engineer suggests replacement, and so it shall be. The instrument has been in operation for 6 years.