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).