On 01/08/2016 11:39 AM, Steve Wilson wrote:> John Larkin <jjlarkin@highlandtechnology.com> wrote: > >> Mine's pretty steady at 1 pF full scale. The most sensitive current >> range, 1e-14 amps full scale, looks useless. It drifts like crazy and >> tiny mechanical forces on the case move it several fA. > > Follow-up: On 6/2/14, discussing replacing the input stage to reduce drift, > you said > > 610C uses mosfets. Mine seems very stable. > > http://www.electronics- > related.com/showthread/sci.electronics.design/447217-11.php > > Which is it - drift or no drift? >Well, the full scale range is switchable from 10 femtoamps to 300 milliamps, so the correct answer is "yes". Super nice meter though. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Keithley 610C repair
Started by ●December 1, 2015
Reply by ●January 8, 20162016-01-08
Reply by ●January 9, 20162016-01-09
John Larkin <jjlarkin@highlandtechnology.com> wrote:> On Fri, 08 Jan 2016 16:39:52 GMT, Steve Wilson <no@spam.com> wrote: > >>John Larkin <jjlarkin@highlandtechnology.com> wrote: >> >>> Mine's pretty steady at 1 pF full scale. The most sensitive current >>> range, 1e-14 amps full scale, looks useless. It drifts like crazy >>> and tiny mechanical forces on the case move it several fA. >> >>Follow-up: On 6/2/14, discussing replacing the input stage to reduce >>drift, you said >> >>610C uses mosfets. Mine seems very stable. >> >>http://www.electronics- >>related.com/showthread/sci.electronics.design/447217-11.php >> >>Which is it - drift or no drift? > > Stable on the 1 pA range. Unstable on the 10 fA range.The discussion was improving the drift on the 10 fA range. You knew that.
Reply by ●January 9, 20162016-01-09
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> On 01/08/2016 11:39 AM, Steve Wilson wrote: >> John Larkin <jjlarkin@highlandtechnology.com> wrote: >> >>> Mine's pretty steady at 1 pF full scale. The most sensitive current >>> range, 1e-14 amps full scale, looks useless. It drifts like crazy >>> and tiny mechanical forces on the case move it several fA. >> >> Follow-up: On 6/2/14, discussing replacing the input stage to reduce >> drift, you said >> >> 610C uses mosfets. Mine seems very stable. >> >> http://www.electronics- >> related.com/showthread/sci.electronics.design/447217-11.php >> >> Which is it - drift or no drift? >> > > Well, the full scale range is switchable from 10 femtoamps to 300 > milliamps, so the correct answer is "yes".The discussion was to find ways to improve the drift on the 10 fA range. Would your customers let you get away with such an answer?> Super nice meter though. > > Cheers > > Phil Hobbs >
Reply by ●January 9, 20162016-01-09
On Sun, 10 Jan 2016 01:28:39 GMT, Steve Wilson <no@spam.com> wrote:>John Larkin <jjlarkin@highlandtechnology.com> wrote: > >> On Fri, 08 Jan 2016 16:39:52 GMT, Steve Wilson <no@spam.com> wrote: >> >>>John Larkin <jjlarkin@highlandtechnology.com> wrote: >>> >>>> Mine's pretty steady at 1 pF full scale. The most sensitive current >>>> range, 1e-14 amps full scale, looks useless. It drifts like crazy >>>> and tiny mechanical forces on the case move it several fA. >>> >>>Follow-up: On 6/2/14, discussing replacing the input stage to reduce >>>drift, you said >>> >>>610C uses mosfets. Mine seems very stable. >>> >>>http://www.electronics- >>>related.com/showthread/sci.electronics.design/447217-11.php >>> >>>Which is it - drift or no drift? >> >> Stable on the 1 pA range. Unstable on the 10 fA range. > >The discussion was improving the drift on the 10 fA range. > >You knew that.Actually, I didn't. I'm seeing only a small, recent piece of the thread. I don't think the mosfets are the problem on the lowest ranges. The problem seems to be random charge transfers and maybe leakages. At heart, the mosfets are the front-end of a voltmeter. On voltage-input ranges, even with the multiplier cranked all the way up, it's stable. So the fets aren't drifting. They might be leaking, but I doubt that. A little pressure on the side of the box, bending the metal a tiny bit, makes the 10fA range go wild. Mosfets aren't doing that. My home-made pA meter was more stable, maybe because there wasn't so much stuff inside to make e-fields. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●January 9, 20162016-01-09
John Larkin wrote...> > My home-made pA meter was more stable, maybe because > there wasn't so much stuff inside to make e-fields.And, no range-changing stuff, right? -- Thanks, - Win
Reply by ●January 9, 20162016-01-09
On 9 Jan 2016 19:01:19 -0800, Winfield Hill <hill@rowland.harvard.edu> wrote:>John Larkin wrote... >> >> My home-made pA meter was more stable, maybe because >> there wasn't so much stuff inside to make e-fields. > > And, no range-changing stuff, right?Sure it changes ranges. By plugging different resistors, on Pomona plugs, into one set of jacks. https://dl.dropboxusercontent.com/u/53724080/Gear/Z260_pA/99A260A1.JPG https://dl.dropboxusercontent.com/u/53724080/Gear/Z260_pA/99A260A3.JPG https://dl.dropboxusercontent.com/u/53724080/Gear/Z260_pA/99S260A.JPG I have Z1 plugin resistors from 1K to 1T. The lexan was added after I discovered that those binding posts are super leaky. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●January 10, 20162016-01-10
On Sat, 09 Jan 2016 19:57:45 -0800, John Larkin <jjlarkin@highlandtechnology.com> wrote:>On 9 Jan 2016 19:01:19 -0800, Winfield Hill <hill@rowland.harvard.edu> >wrote: > >>John Larkin wrote... >>> >>> My home-made pA meter was more stable, maybe because >>> there wasn't so much stuff inside to make e-fields. >> >> And, no range-changing stuff, right? > >Sure it changes ranges. By plugging different resistors, on Pomona >plugs, into one set of jacks. > >https://dl.dropboxusercontent.com/u/53724080/Gear/Z260_pA/99A260A1.JPG > >https://dl.dropboxusercontent.com/u/53724080/Gear/Z260_pA/99A260A3.JPG > >https://dl.dropboxusercontent.com/u/53724080/Gear/Z260_pA/99S260A.JPG > >I have Z1 plugin resistors from 1K to 1T. > >The lexan was added after I discovered that those binding posts are >super leaky.Hang on to that Wall wart. THey don't make transformer warts anymore, just noisy swithers. ;) Cheers
Reply by ●January 10, 20162016-01-10
>> Well, the full scale range is switchable from 10 femtoamps to 300 >> milliamps, so the correct answer is "yes".>The discussion was to find ways to improve the drift on the 10 fA range.>Would your customers let you get away with such an answer?I don't recall ever having been asked such a stupid and hostile question by a customer. Cheers Phil Hobbs
Reply by ●January 10, 20162016-01-10
On 01/09/2016 08:45 PM, John Larkin wrote: <snip>> I don't think the mosfets are the problem on the lowest ranges. The > problem seems to be random charge transfers and maybe leakages. > > At heart, the mosfets are the front-end of a voltmeter. On > voltage-input ranges, even with the multiplier cranked all the way up, > it's stable. So the fets aren't drifting. They might be leaking, but I > doubt that. A little pressure on the side of the box, bending the > metal a tiny bit, makes the 10fA range go wild. Mosfets aren't doing > that.I think it's mostly mechanical instability combined with fairly large internal E fields. The power supplies are +- 55V or something, and all the resistors are hanging in midair. If you've got 100V gradients running around, with a node capacitance of 5 pF and a typical separation of an inch, you can get 10-fA currents from a velocity of ~ 25 mm * 10 fA / (100V*5pF) = 0.5 microns per second. That's an average, of course, so in real life the motions would have to be much bigger. Still, it makes sense that flexing the front panel (where the switch is mounted) by a millimetre or so might make it go nuts. A bit of strategically placed foil inside would probably help a lot.> My home-made pA meter was more stable, maybe because there wasn't so > much stuff inside to make e-fields.The combination of a 100-fA FS homebrew box and a 610C is a pretty good solution. I like your pluggable thing, which is nice and flexible. For current measurements, making the loops and nodes smaller would make it faster and more stable, so I'd lean towards a fixed 1T resistor and a metal box meself. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●January 10, 20162016-01-10
On Sat, 09 Jan 2016 23:14:51 -0500, Martin Riddle <martin_ridd@verizon.net> wrote:>On Sat, 09 Jan 2016 19:57:45 -0800, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > >>On 9 Jan 2016 19:01:19 -0800, Winfield Hill <hill@rowland.harvard.edu> >>wrote: >> >>>John Larkin wrote... >>>> >>>> My home-made pA meter was more stable, maybe because >>>> there wasn't so much stuff inside to make e-fields. >>> >>> And, no range-changing stuff, right? >> >>Sure it changes ranges. By plugging different resistors, on Pomona >>plugs, into one set of jacks. >> >>https://dl.dropboxusercontent.com/u/53724080/Gear/Z260_pA/99A260A1.JPG >> >>https://dl.dropboxusercontent.com/u/53724080/Gear/Z260_pA/99A260A3.JPG >> >>https://dl.dropboxusercontent.com/u/53724080/Gear/Z260_pA/99S260A.JPG >> >>I have Z1 plugin resistors from 1K to 1T. >> >>The lexan was added after I discovered that those binding posts are >>super leaky. > >Hang on to that Wall wart. THey don't make transformer warts anymore, >just noisy swithers. ;) > >CheersWe have a big box that must have 100 old warts in it. We really should throw some of that junk away, but you never know when you'll need a 17 volt AC wart. -- John Larkin Highland Technology, Inc lunatic fringe electronics
