Author Topic: SX100 saturation oddity  (Read 641 times)

neko

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SX100 saturation oddity
« on: October 09, 2018, 10:33:55 am »
So our probe has had the W-filament turned off since Saturday, sealed up with GV1. Today I turn on the machine and for some reason, saturation is down. Way down. It was 216, and today it wont steadily regulate until I dropped down to 211. Which seemed weird, then I realized the probe hadn't been rebooted in over a month, so I kicked it over, and rebooted the computer as well because, hey, it's windows XP.

Lo and behold, saturation is right back at 216. I'm assuming it's just something to do with an aging (16 years!) probe but if anyone has any ideas as to what the cause might be, I'm all ears. I had a problem a couple years back with the power supply on the condenser lenses, one of the symptoms of which was difficulty regulating the beam properly, but none of the other symptoms of that have shown up and the condenser lens power supply is new as of 2016, and these disregulation events I'm having now are much more subtle than when the condensers were the culprit (it's a gentle ramp now, previously it looked more like a tidal wave and would go up then drop drastically).

Our beam regulation aperture could use a replacement, it's about two years old, but that shouldn't have anything to do with stability if changing the heat values will land it in an island of stability, right? Once the beam is stable it regulates to within a few tens of pA, and last time I did a long test it was stable in that range for over an hour.

Maybe some capacitor somewhere is dying? Anyway I'm not going to worry about it too much if rebooting fixes it, unless it's a problem with a semi-known solution I'm just going to put a monthly reboot day on the ol' work calendar and hope a new probe is a few years in my future.

EDIT: just remember the HI aligment values were significantly different (eg not within daily drift error, off by a couple hundred units) from what they'd been previously (the LO was within error though), and after resetting the electronics, the 211 heat was vastly off from even the significant difference earlier in the day, but after going back to 216 the alignment values are very close to what they had previously been. But I didn't think to write them down because I wasn't actually expecting the reset to fix anything, I was just doing it because I remembered it had been a while. If PfE logs the alignment I'm gonna send John cookies, and if not I'd use the API to write my own logger (in that magic future where I acquire PfE, that is).
« Last Edit: October 09, 2018, 10:52:59 am by neko »

Probeman

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Re: SX100 saturation oddity
« Reply #1 on: October 09, 2018, 02:05:27 pm »
We had to replace the original Cameca supplied Dell computer running XP because the little capacitors on the motherboard kept failing.  And failing caps on your motherboard could easily cause all sorts of issues with the OS and apps and we did see all sorts of weird stuff on our XP computer until we finally figured out that we had to replace the caps on the motherboard.

Unfortunately Cameca had provided us with the less expensive Dell Optiplex business grade computer that has these crappy capacitors that pop after running for 5 or 6 years.  Finally we bought a new Precision Workstation class computer with Win 7 and this mother board has tantalum capacitors which can run forever.

Hope this helps.
john
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neko

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Re: SX100 saturation oddity
« Reply #2 on: October 12, 2018, 09:12:53 am »
Oh sorry, I meant rebooting the probe, not the computer (which I reboot just because I do that every few weeks anyway). The computer is a Precision T3600 because I've got decades of experience with lower quality Dells in my past life as a computer consultant. Unless it was somehow a software glitch that caused the input heat values to output drastically different values suddenly, which would be quite news to me but, that's aging software for ya. If only I'd rebooted only the probe... but I was in a hurry trying to get back to work.

My suspicion is that there's a capacitor somewhere in the regulation system or condenser system that's aging and after a while starts to go out of whack... I've also had the saturation go up and down on me over time (with this same filament and others) so the next time I see it doing that I'm going to reset the electronics and see what happens.

neko

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Re: SX100 saturation oddity
« Reply #3 on: January 25, 2019, 11:10:52 am »
I've done a little bit more poking around on this (as well as just rebooting the probe electronics every week or two) and what I'm finding is that the input vs measured heat values are changing, and affected by electronics reboots.

Yesterday the input was 223 and the measured was 240. This morning, after I rebooted and re-loaded the beam file, the input was 223 and the measured was 242. I had been at around 219 the last time I rebooted and the input heat slowly crept up until today's reboot. I hadn't been measuring and logging the heat, only recording the input values, but I have started measuring and recording both so I can track how this system is behaving over time. Interestingly, today the system is stable at 219/236.

I use the SXTest program looking for a horizontal line on the order of 10 minutes to determine saturation/stability these days, as the other methods (gun scan hi or watching the nA change) don't always produce a fully stable beam the way I like to see it. I would use the recorder program but there seems to be a problem with it in my version of the software.