On Fri, 11 Dec 2015 08:56:54 -0800, John Larkin <jjlarkin@highlandtechnology.com> wrote:>It's a beautiful instrument, as long as you don't look inside. It's >sort of a rat's nest.--- Lack of beauty is in the eye of the beholder, and if one can't appreciate the underpinning of the builder's reasons for constructing its nest in a certain way doesn't detract from its beauty. --->The change you are seeing on the mylar cap may be dielectric >absorption, maybe not leakage. They are awful that way.--- "may be" and "maybe not" sound like ignorance in that dielectric absorbtion results in an increase in voltage across the capacitor's terminals once it's been discharged, while leakage results in the lowering of voltage across the capacitor's terminals due to electron migration through its dielectric. --->Someone here once posted a long-term measurement of film cap leakage, >and as I recall he saw essentially zero voltage change per year for >some.--- A link corroberating your opinion would be nice, since your opinion is somewhat suspect. John Fields
Keithley 610C repair
Started by ●December 1, 2015
Reply by ●December 11, 20152015-12-11
Reply by ●December 11, 20152015-12-11
On Friday, December 11, 2015 at 8:01:47 PM UTC-5, John Larkin wrote:> On Fri, 11 Dec 2015 19:18:37 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >On 12/11/2015 06:51 PM, John Larkin wrote: > >> On Fri, 11 Dec 2015 18:18:05 -0500, Phil Hobbs > >> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> > >>> On 12/11/2015 11:56 AM, John Larkin wrote: > >>>> On Fri, 11 Dec 2015 11:50:08 -0500, Phil Hobbs > >>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>>> > >>>>> On 12/10/2015 07:25 PM, Phil Hobbs wrote: > >>>>>> On 12/10/2015 03:51 PM, John Larkin wrote: > >>>>>>> On Thu, 10 Dec 2015 13:46:24 -0500, Phil Hobbs > >>>>>>> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>>>>>> > >>>>>>>> On 12/10/2015 01:41 PM, John Larkin wrote: > >>>>>>>>> On Thu, 10 Dec 2015 05:11:41 -0800 (PST), Phil Hobbs > >>>>>>>>> <pcdhobbs@gmail.com> wrote: > >>>>>>>>> > >>>>>>>>>>> Teflon and some ceramics are the best capacitor types; 100 pF > >>>>>>>>>>> gives you > >>>>>>>>>> Iout = (1e-10) dV/dt > >>>>>>>>>>> and I've made ramp generators that did about 10 mv/hour, and can keep > >>>>>>>>>>> it up all day. that'd be Iout in the 3e-16 amps range... > >>>>>>>>>> > >>>>>>>>>> HP 3325As make nice ramps down to 1 uHz, and they're nearly as > >>>>>>>>>> cheap as 610Cs. It's not a modern DDS/arb architecture, so I don't > >>>>>>>>>> think its output is a staircase. > >>>>>>>>>> > >>>>>>>>>> > >>>>>>>>>> Cheers > >>>>>>>>>> > >>>>>>>>>> Phil Hobbs > >>>>>>>>> > >>>>>>>>> You could charge a 10 uF cap through a 1G resistor, and couple that > >>>>>>>>> into a picoammeter through a 10 pF cap. 10 volts makes 10 nA which > >>>>>>>>> becomes 10 fA. > >>>>>>>>> > >>>>>>>>> > >>>>>>>>> > >>>>>>>>> > >>>>>>>> > >>>>>>>> Ceramic caps that big are pretty nonlinear to use for calibration, no? > >>>>>>>> I have some 2-uf 200V dogbone mylars. When my 610C gets here this > >>>>>>>> evening I'll test their insulation resistance. ;) > >>>>>>> > >>>>>>> A 10 pF NPO should be pretty good on the output side. I'd use a film > >>>>>>> cap for the big one. > >>>>>>> > >>>>>>> > >>>>>>>> > >>>>>>>> An LM662 triangle wave generator with one of your patented > >>>>>>>> bootstrapped-voltage-references could go pretty slowly. > >>>>>>>> > >>>>>>> > >>>>>>> Yeah, if you want a linear ramp a bootstrap current source is a good > >>>>>>> way to go, almost the only way to go if you want, say, 1 nA. > >>>>>>> > >>>>>>> Film cap, cmos opamp follower, bandgap level shifter, 1G resistor back > >>>>>>> to the cap. Reset it with a paper clip. > >>>>>> > >>>>>> > >>>>>> The $125 610C arrived just now, by UPS ground all the way from SoCal. At > >>>>>> first blush, it looks like it works pretty well. It zeroes fine, which > >>>>>> is one of the main indications of health. No trace of stickiness in the > >>>>>> meter movement, which is another important indication. > >>>>>> > >>>>>> On the 10 fA FS range, with the input disconnected but with the cap off > >>>>>> the connector, waving my hand a foot away from the front panel makes the > >>>>>> meter move all over the place. > >>>>>> > >>>>>> Works on both the slow and fast settings. > >>>>>> > >>>>>> Very pretty! > >>>>>> > >>>>> > >>>>> Resistance reads about 2% low up to 1E12 ohms, calibrated using a 5-1/2 > >>>>> digit, 10M DVM and a 10V HP precision power supply. A Russian 1 teraohm > >>>>> 10% resistor reads about 0.86 Tohms on the 610C and about 0.89 Tohms > >>>>> using the digital voltmeter trick. The fast setting pegs the meter in > >>>>> the resistance mode. (I didn't try re-zeroing it.) > >>>>> > >>>>> Voltage is within 1% where I looked. > >>>>> > >>>>> Stability is excellent--on the 10 fA FS range, it stays zeroed to within > >>>>> 1% of FS over several minutes, and that's after only about half an hour > >>>>> of warm-up. > >>>>> > >>>>> With a 100 pF polystyrene cap across the input (just so I know roughly > >>>>> what the capacitance is there), and measuring the 0-3V output on the > >>>>> back near full scale (2.986V), the voltage decay is less than 100 > >>>>> uV/min and is consistent with zero. > >>>>> > >>>>> That means the input current on the 10V range is less than > >>>>> 100uV * 10V/3V * 100 pF /60 s = 0.5 fA. Amazing. (Not bad on the > >>>>> polystyrene, either.) > >>>>> > >>>>> I measured a 2.2 uF 600V wound mylar, charged to 10V for a few seconds. > >>>>> On the 10-V range, it produced nearly full scale on the 0-3V DC output. > >>>>> This output dropped about 220uV out of 3V in 3 minutes, for a > >>>>> self-discharge time constant of about 2.4 million seconds (about a > >>>>> month). So with a 47 G resistor and an LM662, you could actually make a > >>>>> decent 10 microhertz sawtooth out of it. > >>>>> > >>>>> Not a bad gizmo for $125 plus $25 shipping! > >>>>> > >>>>> Cheers > >>>>> > >>>>> Phil Hobbs > >>>> > >>>> It's a beautiful instrument, as long as you don't look inside. It's > >>>> sort of a rat's nest. > >>>> > >>>> The change you are seeing on the mylar cap may be dielectric > >>>> absorption, maybe not leakage. They are awful that way. > >>>> > >>>> Someone here once posted a long-term measurement of film cap leakage, > >>>> and as I recall he saw essentially zero voltage change per year for > >>>> some. > >>>> > >>>> > >>>> > >>> > >>> Interestingly the major source of instability on the 10 fA range appears > >>> to be slow capacitive pickup from things moving around inside as it > >>> warms up. You can make it move > 10 fA in each direction by pressing > >>> gently on the front panel. Pushing on the range switch knob is about > >>> 10x more sensitive. > >>> > >>> When you're down in the hundreds of electrons, these things matter! > >>> > >>> Cheers > >>> > >>> Phil Hobbs > >> > >> 1 fA is 6000 of them per second. > > > >Yup. The meter is a bit faster than that, of course, and the > >fluctuations are smaller than 1/10 of full scale (fun). > >> > >> Hey, back to the flame detector. What does a typical flame sound like? > >> On o/e converter and some headphones might be interesting. Burning > >> cotton must have features. > > > >Diffusion flames such as candles and small sparks are pretty quiet, I > >expect. Certainly quiet compared with all the vibrating duct work and > >reciprocating machinery and cussing workers. ;) > > > >> > >> Imagine listening to a fireworks display, or a sparkler, or a gunshot, > >> or a fountain. Lightning. > >> > >> When I was a kid, I used to walk around listening to magnetic fields > >> and electric fields and light. I was a weird kid. > > > >When did that end? > > > >Cheers > > > >Phil Hobbs > > Being a kid, or being weird? Neither. > > > -- > > John Larkin Highland Technology, Inc > picosecond timing precision measurement > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.comYou should "be a kid" for as much time as you can afford. For me being a kid is playing around with circuits and instruments... all that good stuff. Not to be too much of a downer, but my poor mum with alzheimer's is turning into a kid, which totally sucks. sorry, George H. My poor mum, is turning into a kid too. Which pretty much sucks, (sorry for any downer.)
Reply by ●December 12, 20152015-12-12
>"may be" and "maybe not" sound like ignorance in that dielectric >absorbtion results in an increase in voltage across the capacitor's >terminals once it's been discharged,Sometimes our desire to score points off those we dislike can lead us to say silly things like that. Dielectric absorption is a linear process, so it occurs on both charge and discharge. One common model is a bunch of series RCs with different TCs, arranged in parallel. Pease's article on soakage is a good intro. If there are long TCs in the model, then in order to measure the actual leakage, you have to charge the cap from the supply for several times the longest TC that contributes at the level of your desired accuracy. I charged the cap for only a few seconds, but was measuring the decay over several minutes, so dielectric absorption may well have contributed significantly.>while leakage results in the >lowering of voltage across the capacitor's terminals due to electron >migration through its dielectric.Cheers Phil Hobbs
Reply by ●December 12, 20152015-12-12
On Fri, 11 Dec 2015 19:15:03 -0600, John Fields <jfields@austininstruments.com> wrote:>On Fri, 11 Dec 2015 08:56:54 -0800, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > > >>It's a beautiful instrument, as long as you don't look inside. It's >>sort of a rat's nest. > >--- >Lack of beauty is in the eye of the beholder, and if one can't >appreciate the underpinning of the builder's reasons for constructing >its nest in a certain way doesn't detract from its beauty. >--- > >>The change you are seeing on the mylar cap may be dielectric >>absorption, maybe not leakage. They are awful that way. > >--- >"may be" and "maybe not" sound like ignorance in that dielectric >absorbtion results in an increase in voltage across the capacitor's >terminals once it's been discharged, while leakage results in the >lowering of voltage across the capacitor's terminals due to electron >migration through its dielectric.You finally said something about electronics! It's wrong, of course.
Reply by ●December 12, 20152015-12-12
On Sat, 12 Dec 2015 08:28:13 -0800, John Larkin <jjlarkin@highlandtechnology.com> wrote:>On Fri, 11 Dec 2015 19:15:03 -0600, John Fields ><jfields@austininstruments.com> wrote: > >>On Fri, 11 Dec 2015 08:56:54 -0800, John Larkin >><jjlarkin@highlandtechnology.com> wrote: >> >> >>>It's a beautiful instrument, as long as you don't look inside. It's >>>sort of a rat's nest. >> >>--- >>Lack of beauty is in the eye of the beholder, and if one can't >>appreciate the underpinning of the builder's reasons for constructing >>its nest in a certain way doesn't detract from its beauty. >>--- >> >>>The change you are seeing on the mylar cap may be dielectric >>>absorption, maybe not leakage. They are awful that way. >> >>--- >>"may be" and "maybe not" sound like ignorance in that dielectric >>absorbtion results in an increase in voltage across the capacitor's >>terminals once it's been discharged, while leakage results in the >>lowering of voltage across the capacitor's terminals due to electron >>migration through its dielectric. > > >You finally said something about electronics! It's wrong, of course.--- How so? JF
Reply by ●December 12, 20152015-12-12
On Sat, 12 Dec 2015 18:29:49 -0600, John Fields <jfields@austininstruments.com> wrote:>On Sat, 12 Dec 2015 08:28:13 -0800, John Larkin ><jjlarkin@highlandtechnology.com> wrote: > >>On Fri, 11 Dec 2015 19:15:03 -0600, John Fields >><jfields@austininstruments.com> wrote: >> >>>On Fri, 11 Dec 2015 08:56:54 -0800, John Larkin >>><jjlarkin@highlandtechnology.com> wrote: >>> >>> >>>>It's a beautiful instrument, as long as you don't look inside. It's >>>>sort of a rat's nest. >>> >>>--- >>>Lack of beauty is in the eye of the beholder, and if one can't >>>appreciate the underpinning of the builder's reasons for constructing >>>its nest in a certain way doesn't detract from its beauty. >>>--- >>> >>>>The change you are seeing on the mylar cap may be dielectric >>>>absorption, maybe not leakage. They are awful that way. >>> >>>--- >>>"may be" and "maybe not" sound like ignorance in that dielectric >>>absorbtion results in an increase in voltage across the capacitor's >>>terminals once it's been discharged, while leakage results in the >>>lowering of voltage across the capacitor's terminals due to electron >>>migration through its dielectric. >> >> >>You finally said something about electronics! It's wrong, of course. > >--- >How so? > >JFBecause DA could explain the voltage sag that Phil observed. He explained that to you. DA doesn't just happen at zero volts; look up the circuit model for a cap with DA. Phil might be seeing leakage and he might be seeing DA; that was all I said. Not having his cap, I can't tell from here. He could observe the voltage vs time and resolve which is happening, if he cares to. DA would have a different curve than leakage. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Reply by ●December 17, 20152015-12-17
John Larkin wrote:> On Sat, 12 Dec 2015 18:29:49 -0600, John Fields > <jfields@austininstruments.com> wrote: > >> On Sat, 12 Dec 2015 08:28:13 -0800, John Larkin >> <jjlarkin@highlandtechnology.com> wrote: >> >>> On Fri, 11 Dec 2015 19:15:03 -0600, John Fields >>> <jfields@austininstruments.com> wrote: >>> >>>> On Fri, 11 Dec 2015 08:56:54 -0800, John Larkin >>>> <jjlarkin@highlandtechnology.com> wrote: >>>> >>>> >>>>> It's a beautiful instrument, as long as you don't look inside. It's >>>>> sort of a rat's nest. >>>> >>>> --- >>>> Lack of beauty is in the eye of the beholder, and if one can't >>>> appreciate the underpinning of the builder's reasons for constructing >>>> its nest in a certain way doesn't detract from its beauty. >>>> --- >>>> >>>>> The change you are seeing on the mylar cap may be dielectric >>>>> absorption, maybe not leakage. They are awful that way. >>>> >>>> --- >>>> "may be" and "maybe not" sound like ignorance in that dielectric >>>> absorbtion results in an increase in voltage across the capacitor's >>>> terminals once it's been discharged, while leakage results in the >>>> lowering of voltage across the capacitor's terminals due to electron >>>> migration through its dielectric. >>> >>> >>> You finally said something about electronics! It's wrong, of course. >> >> --- >> How so? >> >> JF > > Because DA could explain the voltage sag that Phil observed. He > explained that to you. > > DA doesn't just happen at zero volts; look up the circuit model for a > cap with DA. Phil might be seeing leakage and he might be seeing DA; > that was all I said. Not having his cap, I can't tell from here. > > He could observe the voltage vs time and resolve which is happening, > if he cares to. DA would have a different curve than leakage. > >Why bother explaining such fundamental stuff?
Reply by ●December 17, 20152015-12-17
On Wed, 16 Dec 2015 23:02:55 -0800, Robert Baer <robertbaer@localnet.com> wrote:>John Larkin wrote: >> On Sat, 12 Dec 2015 18:29:49 -0600, John Fields >> <jfields@austininstruments.com> wrote: >> >>> On Sat, 12 Dec 2015 08:28:13 -0800, John Larkin >>> <jjlarkin@highlandtechnology.com> wrote: >>> >>>> On Fri, 11 Dec 2015 19:15:03 -0600, John Fields >>>> <jfields@austininstruments.com> wrote: >>>> >>>>> On Fri, 11 Dec 2015 08:56:54 -0800, John Larkin >>>>> <jjlarkin@highlandtechnology.com> wrote: >>>>> >>>>> >>>>>> It's a beautiful instrument, as long as you don't look inside. It's >>>>>> sort of a rat's nest. >>>>> >>>>> --- >>>>> Lack of beauty is in the eye of the beholder, and if one can't >>>>> appreciate the underpinning of the builder's reasons for constructing >>>>> its nest in a certain way doesn't detract from its beauty. >>>>> --- >>>>> >>>>>> The change you are seeing on the mylar cap may be dielectric >>>>>> absorption, maybe not leakage. They are awful that way. >>>>> >>>>> --- >>>>> "may be" and "maybe not" sound like ignorance in that dielectric >>>>> absorbtion results in an increase in voltage across the capacitor's >>>>> terminals once it's been discharged, while leakage results in the >>>>> lowering of voltage across the capacitor's terminals due to electron >>>>> migration through its dielectric. >>>> >>>> >>>> You finally said something about electronics! It's wrong, of course. >>> >>> --- >>> How so? >>> >>> JF >> >> Because DA could explain the voltage sag that Phil observed. He >> explained that to you. >> >> DA doesn't just happen at zero volts; look up the circuit model for a >> cap with DA. Phil might be seeing leakage and he might be seeing DA; >> that was all I said. Not having his cap, I can't tell from here. >> >> He could observe the voltage vs time and resolve which is happening, >> if he cares to. DA would have a different curve than leakage. >> >> > Why bother explaining such fundamental stuff?More to the point, I should just ignore Fields. He doesn't care about electronics.
Reply by ●January 8, 20162016-01-08
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?
Reply by ●January 8, 20162016-01-08
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. -- John Larkin Highland Technology, Inc lunatic fringe electronics
