On 01/01/2022 01:19, whit3rd wrote:> On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote: >> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote: > >>> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html >>> >>> the circuit needs a closed DC path in order for current to flow. > > > >> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react >> to the microvolt output of something like this? -- thanks > > <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html> > > A moving-needle meter for 30 uA with 100 ohms internal resistance can cover the > 3mV range, with 30 uV easily resolved. Add a battery for collector bias, and > use a low-noise transistor B-E instead of one diode, and you're good for lower signals. > > So low, in fact, that some frequency tuning is a wise addition.Excuse my ignorance, but why in the "Description" does it say that it's a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive Range: -300-0-300μA"? And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is connected in series in the circuit, the higher end of the "G" terminal is used." That would give it an FSD of 72mV, wouldn't it? Is there a reason why it's 2.4kohm rather than another value? -- Jeff
Field strength meter -- diode
Started by ●December 31, 2021
Reply by ●January 1, 20222022-01-01
Reply by ●January 1, 20222022-01-01
On Friday, December 31, 2021 at 11:56:07 PM UTC-8, Jeff Layman wrote:> On 01/01/2022 01:19, whit3rd wrote: > > On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote: > >> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote: > > > >>> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html > >>> > >>> the circuit needs a closed DC path in order for current to flow. > > > > > > > >> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react > >> to the microvolt output of something like this? -- thanks > > > > <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html>> Excuse my ignorance, but why in the "Description" does it say that it's > a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive > Range: -300-0-300μA"?Yeah, that's a mystery.> And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is > connected in series in the circuit, the higher end of the "G" terminal > is used." That would give it an FSD of 72mV, wouldn't it? Is there a > reason why it's 2.4kohm rather than another value?It's usual in these things to provide some damping (a shunt resistor or R-C snubber) across the bare galvanometer, and there's a particular value that (with the coil inductance) is most effective. That's the only resistor value I'd expect to see built-in. The merchant might not know what it's for, but damping makes the needle return to zero between measurements instead of oscillating for a few seconds.
Reply by ●January 1, 20222022-01-01
On 01/01/2022 08:28, whit3rd wrote:> On Friday, December 31, 2021 at 11:56:07 PM UTC-8, Jeff Layman wrote: >> On 01/01/2022 01:19, whit3rd wrote: >>> On Friday, December 31, 2021 at 12:47:23 PM UTC-8, mkr5000 wrote: >>>> On Friday, December 31, 2021 at 2:33:46 PM UTC-5, Rich S wrote: >>> >>>>> https://coolcircuits.blogspot.com/2011/03/field-strength-meter.html >>>>> >>>>> the circuit needs a closed DC path in order for current to flow. >>> >>> >>> >>>> Would there be a simple transistor amp (or an op amp possibly) that would be sensitive enough to react >>>> to the microvolt output of something like this? -- thanks >>> >>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sensor-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.html> > >> Excuse my ignorance, but why in the "Description" does it say that it's >> a "-30-0-30µA Galvanometer", but in the "Specification" say "Sensitive >> Range: -300-0-300μA"? > > Yeah, that's a mystery.Probably just a misprint or mistranslation.>> And what is the 2.4kohm resistor for? "Instruction" 2 states "When it is >> connected in series in the circuit, the higher end of the "G" terminal >> is used." That would give it an FSD of 72mV, wouldn't it? Is there a >> reason why it's 2.4kohm rather than another value? > > It's usual in these things to provide some damping (a shunt resistor or R-C > snubber) across the bare galvanometer, and there's a particular value > that (with the coil inductance) is most effective. That's the only > resistor value I'd expect to see built-in. The merchant might not > know what it's for, but damping makes the needle return to zero > between measurements instead of oscillating for a few seconds.OK. Makes sense. Just don't try try to push it to -300-0-300μA! :-) -- Jeff
Reply by ●January 1, 20222022-01-01
Jan Frank wrote:> whit3rd <whit3rd@gmail.com> wrote: > >> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Senso >> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415.ht >> ml> > > The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in > parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift. > > With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps. > > My favorite electrometer is the Kiethley 610C, which only goes down to 1e- > 11 A full scale, and drifts like hell.Nah, there's the range multiplier knob that gets you another factor of 100 on the FS range, so you get a 10-fA FSR on that box. Of course that one is too unstable to be useful, but the 100-fA FS range is pretty good, at least on my unit. Yours may need cleaning or repair. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●January 2, 20222022-01-02
Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> Jan Frank wrote: >> whit3rd <whit3rd@gmail.com> wrote: >> >>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen >>> so >>> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415. >>> ht ml> >> >> The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in >> parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift. >> >> With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps. >> >> My favorite electrometer is the Kiethley 610C, which only goes down to >> 1e-11 A full scale, and drifts like hell. > > Nah, there's the range multiplier knob that gets you another factor of > 100 on the FS range, so you get a 10-fA FSR on that box. > > Of course that one is too unstable to be useful, but the 100-fA FS range > is pretty good, at least on my unit. Yours may need cleaning or repair. > > Cheers > > Phil HobbsThere is no change when the range switch is partially rotated, so I don't think it is the problem. The reading simply wanders, and it gets worse as you go downrange. Obviously thermal drift. I was thinking of replacing the input transistors with an LMC660 or modern equivalent and may do so if I ever need to monitor weak currents over a period of time. But a better option would be to get a used 616 which offers autoranging and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on eBay - around $295 or so. But for now, the RM109 is more than adequate. It certainly beats the banggood galvanometer.
Reply by ●January 2, 20222022-01-02
On Sunday, January 2, 2022 at 12:50:01 AM UTC-5, Jan Frank wrote:> Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote: > > > Jan Frank wrote: > >> whit3rd <whi...@gmail.com> wrote: > >> > >>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen > >>> so > >>> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415. > >>> ht ml> > >> > >> The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in > >> parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift. > >> > >> With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps. > >> > >> My favorite electrometer is the Kiethley 610C, which only goes down to > >> 1e-11 A full scale, and drifts like hell. > > > > Nah, there's the range multiplier knob that gets you another factor of > > 100 on the FS range, so you get a 10-fA FSR on that box. > > > > Of course that one is too unstable to be useful, but the 100-fA FS range > > is pretty good, at least on my unit. Yours may need cleaning or repair. > > > > Cheers > > > > Phil Hobbs > There is no change when the range switch is partially rotated, so I don't > think it is the problem. The reading simply wanders, and it gets worse as > you go downrange. Obviously thermal drift. > > I was thinking of replacing the input transistors with an LMC660 or modern > equivalent and may do so if I ever need to monitor weak currents over a > period of time. > > But a better option would be to get a used 616 which offers autoranging > and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on > eBay - around $295 or so. But for now, the RM109 is more than adequate. It > certainly beats the banggood galvanometer.I ordered some parts and have yet to breadboard anything yet for a FSM. Got the schottkys and a couple germanium diode varieties, plus an FET. What exactly is the value in this where he 2 diodes in series? Of course it's on youtube so.... https://www.youtube.com/watch?v=kml8pNNGTvU&ab_channel=GEORGECHANIOTAKIS
Reply by ●January 2, 20222022-01-02
Jan Frank wrote:> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> Jan Frank wrote: >>> whit3rd <whit3rd@gmail.com> wrote: >>> >>>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen >>>> so >>>> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415. >>>> ht ml> >>> >>> The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in >>> parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift. >>> >>> With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps. >>> >>> My favorite electrometer is the Kiethley 610C, which only goes down to >>> 1e-11 A full scale, and drifts like hell. >> >> Nah, there's the range multiplier knob that gets you another factor of >> 100 on the FS range, so you get a 10-fA FSR on that box. >> >> Of course that one is too unstable to be useful, but the 100-fA FS range >> is pretty good, at least on my unit. Yours may need cleaning or repair. >> >> Cheers >> >> Phil Hobbs > > There is no change when the range switch is partially rotated, so I don't > think it is the problem. The reading simply wanders, and it gets worse as > you go downrange. Obviously thermal drift.Both JL and I have 610Cs that are far better than that. Yours must broken or badly contaminated. Mine easily measures down to the tens of femtoamps.> I was thinking of replacing the input transistors with an LMC660 or modern > equivalent and may do so if I ever need to monitor weak currents over a > period of time.You can do a good job with that. I've been meaning to build a nice 100-pF charge-dispensing loop electrometer, but so far the 610C or even the old tube-based 405 have been better than good enough.> > But a better option would be to get a used 616 which offers autoranging > and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on; > eBay - around $295 or so.I haven't got a lot of use for a digital electrometer. Down in the picoamps and lower, seeing trends is much more important than high precision, not least because leakages are very unlikely to be stable to 3 sig figures. (Plus I paid $5 plus shipping for my 405, $36 for a 602C, and $125 for the 610C on my bench. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●January 2, 20222022-01-02
On Sun, 2 Jan 2022 09:47:33 -0500, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>Jan Frank wrote: >> Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> Jan Frank wrote: >>>> whit3rd <whit3rd@gmail.com> wrote: >>>> >>>>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen >>>>> so >>>>> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415. >>>>> ht ml> >>>> >>>> The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in >>>> parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift. >>>> >>>> With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps. >>>> >>>> My favorite electrometer is the Kiethley 610C, which only goes down to >>>> 1e-11 A full scale, and drifts like hell. >>> >>> Nah, there's the range multiplier knob that gets you another factor of >>> 100 on the FS range, so you get a 10-fA FSR on that box. >>> >>> Of course that one is too unstable to be useful, but the 100-fA FS range >>> is pretty good, at least on my unit. Yours may need cleaning or repair. >>> >>> Cheers >>> >>> Phil Hobbs >> >> There is no change when the range switch is partially rotated, so I don't >> think it is the problem. The reading simply wanders, and it gets worse as >> you go downrange. Obviously thermal drift. > >Both JL and I have 610Cs that are far better than that. Yours must >broken or badly contaminated. Mine easily measures down to the tens of >femtoamps.The fast feedback mode on mine has never worked, so fA and tohm measurements are super slow, 10s of minutes sometimes. Things have to be shielded or people walking around will pin the needle. I built my own fA parts tester before I got the Keithley, using an LMC6001 cmos opamp. It has less wiring and no switches so tends to be faster. https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0> >> I was thinking of replacing the input transistors with an LMC660 or modern >> equivalent and may do so if I ever need to monitor weak currents over a >> period of time. > >You can do a good job with that. I've been meaning to build a nice >100-pF charge-dispensing loop electrometer, but so far the 610C or even >the old tube-based 405 have been better than good enough. > >> >> But a better option would be to get a used 616 which offers autoranging >> and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on; >> eBay - around $295 or so. > >I haven't got a lot of use for a digital electrometer. Down in the >picoamps and lower, seeing trends is much more important than high >precision, not least because leakages are very unlikely to be stable to >3 sig figures. > >(Plus I paid $5 plus shipping for my 405, $36 for a 602C, and $125 for >the 610C on my bench. > >Cheers > >Phil Hobbs-- I yam what I yam - Popeye
Reply by ●January 2, 20222022-01-02
On Sunday, January 2, 2022 at 11:05:45 AM UTC-5, jla...@highlandsniptechnology.com wrote:> On Sun, 2 Jan 2022 09:47:33 -0500, Phil Hobbs > <pcdhSpamM...@electrooptical.net> wrote: > > >Jan Frank wrote: > >> Phil Hobbs <pcdhSpamM...@electrooptical.net> wrote: > >> > >>> Jan Frank wrote: > >>>> whit3rd <whi...@gmail.com> wrote: > >>>> > >>>>> <https://usa.banggood.com/-30-0-30A-Galvanometer-Scientific-Current-Sen > >>>>> so > >>>>> r-Sensitive-Ammeter-Electric-Current-Detector-Analog-Display-p-1441415. > >>>>> ht ml> > >>>> > >>>> The Richmeter RM109 resolves 1uV on the mV scale. With 100 ohms in > >>>> parallel, it resolves I = E / R = 1e-6 / 100 = 10 nA. It doesn't drift. > >>>> > >>>> With 10 Megohms in parallel, it resolves 1e-6 / 1e7 = 100 Femtoamps. > >>>> > >>>> My favorite electrometer is the Kiethley 610C, which only goes down to > >>>> 1e-11 A full scale, and drifts like hell. > >>> > >>> Nah, there's the range multiplier knob that gets you another factor of > >>> 100 on the FS range, so you get a 10-fA FSR on that box. > >>> > >>> Of course that one is too unstable to be useful, but the 100-fA FS range > >>> is pretty good, at least on my unit. Yours may need cleaning or repair. > >>> > >>> Cheers > >>> > >>> Phil Hobbs > >> > >> There is no change when the range switch is partially rotated, so I don't > >> think it is the problem. The reading simply wanders, and it gets worse as > >> you go downrange. Obviously thermal drift. > > > >Both JL and I have 610Cs that are far better than that. Yours must > >broken or badly contaminated. Mine easily measures down to the tens of > >femtoamps. > The fast feedback mode on mine has never worked, so fA and tohm > measurements are super slow, 10s of minutes sometimes. Things have to > be shielded or people walking around will pin the needle. > > I built my own fA parts tester before I got the Keithley, using an > LMC6001 cmos opamp. It has less wiring and no switches so tends to be > faster. > > https://www.dropbox.com/sh/aj85edzmmrx7ret/AAA6HYPHyVeBrCeKShvq82ega?dl=0 > > > >> I was thinking of replacing the input transistors with an LMC660 or modern > >> equivalent and may do so if I ever need to monitor weak currents over a > >> period of time. > > > >You can do a good job with that. I've been meaning to build a nice > >100-pF charge-dispensing loop electrometer, but so far the 610C or even > >the old tube-based 405 have been better than good enough. > > > >> > >> But a better option would be to get a used 616 which offers autoranging > >> and noise of 2e-15 p-p on the lowest current range. It is pretty cheap on; > >> eBay - around $295 or so. > > > >I haven't got a lot of use for a digital electrometer. Down in the > >picoamps and lower, seeing trends is much more important than high > >precision, not least because leakages are very unlikely to be stable to > >3 sig figures. > > > >(Plus I paid $5 plus shipping for my 405, $36 for a 602C, and $125 for > >the 610C on my bench. > > > >Cheers > > > >Phil Hobbs > > > -- > I yam what I yam - PopeyeMaybe you guys didn't see this but why the (2) diodes in series (4 total) as shown here? Thanks. https://www.youtube.com/watch?v=kml8pNNGTvU&ab_channel=GEORGECHANIOTAKIS
Reply by ●January 2, 20222022-01-02
On Sunday, January 2, 2022 at 9:30:04 AM UTC-8, mkr5000 wrote:> Maybe you guys didn't see this but why the (2) diodes in series (4 total) as shown here? > Thanks. > > https://www.youtube.com/watch?v=kml8pNNGTvU&ab_channel=GEORGECHANIOTAKISProbably to keep the sensitivity low. Read some of the comments; a fluorescent lamp (probably electronic ballast, few kilohertz current fluctuations) reads as REAL hot. What you usually want, is something to read a particular range of frequencies, usually in a known RF band, which means at least a grid-dip meter kind of gizmo. I'm partial to the use of AGC-type amplifiers, where one infers high RF strength from low amplifier bias. So, what I'd find really useful, is a way to put an ADL5906 into my old grid dip meter... <https://www.analog.com/en/products/adl5906.html> but I suspect it's harder to do that, than it was to make a solid-state plugin to replace the tube for output-only GDO functions.
