cost of measuring picoamps

First find out how to do it. Look for books on Electronic Measurements.

(Does a pH meter get down to such low levels?)

Heh heh, you haven't read through a keithley instruments catalog yet have you?

Actually, I have, but it was about 20 years ago. I think I still have the catalogue. As Scrooge says in the Mr.Magoo version of "A Christmas Carol": "Is this the way things have to be or just the way they might be?". In other words, if I buy the device from Keithley, I arrive at a certain figure for the price of measuring picoamps. But there might be other ways without purchasing from Keithley that are cheaper. To illustrate, I've been asking about breakout cables and scavenged printer cables in another thread. But I can also purchase what looks like a very nice breakout cable from

for about $20. I guess I'm not likely to find a Keithley device in a dumpster, but there still might be some middle ground.

Another issue with measuring very small currents is the quality or authenticity of the signal. I know that my TV reception is affected by whether or not I put my feet up, since my body acts like an antenna. So, what affect will it have on a picoamp current and its measurement.

I once looked at a book on patch clamp circuits for measuring electricity connected with living cells and it seemed extremely technical and delicate.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

That makes a lot of sense. Is The Art of Electronics good enough? I also have "Electronic Measurements", 2d ed, by Frederick Emmons Terman and Joseph Mayo Pettit, published in 1952. I got it at a library book sale.

Is there some book you recommend for this?

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

Use LMC6001 operational amplifier from National Semiconductors. This level of current is not to hard. I have done 10^-15A with discrete front end.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

--
Posted via a free Usenet account from http://www.teranews.com
Warning: Do not use Ultimate-Anonymity
They are worthless spamers that are running a scam.

Keithley Instruments publish a small book on low level measurements, obviously with their instruments in mind, but which does contain quite a lot of useful stuff.

It's free to people on their mailing list. If you talk to them nicely, they'll probably send you one, although it'll mean you get all the sales and marketing stuff from then on.

Try to get a personally-addressed copy. IME, organization-, or department-addressed copies tend to get grabbed by whoever opens the mail.

--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
                                             (Stephen Leacock)

Terman and Pettit is a very good start. It's pretty much the standard, although obviously out of date in terms of hardware now.

I also like Radio and Electronic Laboratory Handbook by Marcus Graham Scroggie

I'd google for (ultra low current measurements) or the like for some more modern techniques. I imagine there are FET's that will work for this - or the CA3140E - I have a kit for an insulation tester using that which will measure resistance up to 2200 gigohms.

Thanks for the suggestion. Pardon my ignorance, but I don't know what the terminology "discrete front end" means.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

Fred Abse writes:

I'll look into it. I have a collection of documents from them on various measurements one can do and various experiments. They aren't a book but I could see them being bound as one. I got it from them a couple of decades ago along with a price list. It includes the following items: (1) Electrical Engineering Experiment #1 (Series I). Uses of test instruments: digital multimeter and oscilloscope. Dated 1985. (2) Electrical Engineering Experiment #2 (Series I). Kirchofft's Laws and Thevenin & Norton Equivalent Circuits. (3) Electrical Engineering Experiment #3 (Series I). Linear op amp circuits (4) Electrical Engineering Experiment #4 (Series I). NonLinear op amp circuits (5) Electrical Engineering Experiment #5 (Series I). Transistor amplifiers (6) Electrical Engineering Experiment #6 (Series I). Step response of passive circuits (7) Electrical Engineering Experiment #1 (Series II). Silicon controlled rectifier (8) Electrical Engineering Experiment #2 (Series II). Field effect transistors (9) Electrical Engineering Experiment #3 (Series II). Digital to analog conversion (10) Electrical Engineering Experiment #4 (Series II). Voltage controllable differential current source (11) Electrical Engineering Experiment #5 (Series II). Digital to analog conversion and the operational amplifier (12) Electrical Engineering Experiment #6 (Series II). Conditining a current sourcing device for analog to digital conversion (13) Physics experiment #1. Microcomputer controlled data acquisition and analysis systems (14) Physics experiment #2. Franck-Hertz experiment (This uses, in addition to Keithley equipment, a mercury filled triode available, in 1985, from Klinger Scientific Apparatus, 83-45 Parsons Blvd, Jamaica 32, NY. One of the Keithley items is a Keithley Model 480 Digital Picoammeter selling for $695, in 1985, unless one gets it with the optional IEEE-488 interface mentioned in the experiment, which brings the price up to $1020. Also uses Commodore PET.) (15) Physics Experiment #3. Grating spectrometer-Rydberg constant (16) Physics Experiment #4. Energy gap in a semiconductor (17) Physics Experiment #5. Photoelectric effect (18) Physics Experiment #6. The electric field (19) Physics Experiment #1 (Series II) Franck-Hertz experiment (This specifies a Leybold 555-80 tube or equivalent. I think Klinger and Leybold are connected somehow.) (20) Physics Experiment #2 (Series II) The determination of the B vs H curves and the hysteresis loop of magnetic materials by the Rowland ring ballistic step method (21) Physics Experiment #3 (Series II) The charge of an electron (22) Physics Experiment #4 (Series II) Temperature measuring instrumentation: thermistors (23) Physics Experiment #5 (Series II) Thermocouples and temperature transducers (24) Physics Experiment #6 (Series II) The study of the LED as a light detector

In addition to these, I have one or two dozen application notes on topics ranging from "Guarding vs. Isolation in DMMs" to "Uranium systems calibration for the Keithley model 642 electrometer".

It all seems like valuable information if you can figure out a way around the fact that you can't afford any of the equipment.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

I should have been more clear. I meant a that it had two matched discrete fets hooked up as a differential amplifier followed by an ordinary operational amplifier. For the currents that you are measuring you need not do this.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

void _-void-_ in the obvious place

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Look at the Amateur Scientist column in Scientific American. It's likely to tell you how to do this with a coffee can and a hair net (or similar).

Thanks for the explanation.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

I have C.L.Stong's book, The Amateur Scientist, and I also copied a lot of articles from his column that appeared after the book was published, too many to list here, but maybe I should since it will refresh my memory of what I have and what it really does.

Take the Franck-Hertz tube. I don't know an alternative to purchasing one from Leybold or doing glassblowing to make your own tube. However, I was discussing on sci.chem some possibilities that might make it possible to work with very simple resources. I just don't know whether the ideas can be made to work. By doing electrolysis, you can easily fill a tube with with oxygen, hydrogen or chlorine. You can close the tube at both ends with stoppers that have electrodes poking through them. One of the electrodes might instead be a filament. I think you can do this without letting the gas out and I described the procedure I think would do this in my sci.chem postings in the last week or so. Maybe you need more electrodes, e.g. to simulate a triode and I'm not sure how to insert those without doing glassblowing. I've done a little of that in the past but I don't have a suitable place to work at the moment and don't have any equipment.

Stong does have an article on how to do glassblowing in an article in the early 1960's. Finding a place to it is the problem in that case. I'm looking into it, since I would like to do it and since the skill has other applications, but at the moment I don't have a solution.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

You might see if there is a local artist's area - we have one in our city where they do glass. Or ask a couple of local neon sign makers - they may be able to point you to someone.

I'm trying to follow up on the suggestion of Boris Mohar that I should use a National Semiconductor LCM6001 op amp for this purpose. I looked at Jameco but didn't find this chip there. Who sells it and for how much?

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

--
Perhaps if you used the right part number...

http://www.national.com/search/psearch.cgi?keywords=LMC6001

Perhaps. Being a mathematician, I gravitate to the ordering LCM (least common multiple). The national semiconductor site hangs my browser. I tried it in lynx and got some information. They are talking in terms of selling them in lots of 1000, with a $9.46 rail charge. Jameco doesn't turn up the part. National Semiconductor describes the part as obsolete. What is used now?

I would probably only need to measure nanoamps, since Melissinos' book says that the Franck-Hertz tube would produce nanoamps under the conditions of the experiment. On the other hand, one wants a good picture of the dips, so I feel better about picoamps.

--
Ignorantly,
Allan Adler 
* Disclaimer: I am a guest and *not* a member of the MIT CSAIL. My actions and
* comments do not reflect in any way on MIT. Also, I am nowhere near Boston.

It looks like only some varieties of the part have been discontinued --- the metal-can package and the lowest-quality grade. The plastic-DIP 'AIN' and 'BIN' suffixes are still in full production. (You have to download the datasheet and read through it to find out what the part suffixes mean, annoyingly. It appears that AI/BI/CI are quality grades and N vs. H indicate the package type.)

I plugged the part number into "octopart.com", which searches several distributors, and came up with a number of places to buy the chips in singles for $10-$15.

National has a kind of flaky Flash-based parametric search doodad on their site which suggests their LMP2012 and LMP2015 --- at first glance, similar or better specs to the LMC6001, and cheaper (and newer).

--
   Wim Lewis , Seattle, WA, USA. PGP keyID 27F772C1

Lots of picoamps or sub picoamps bias current are available today.

The LMC608x (10s of fA) might be more common than the older LMC600x

Also Analog and others have plethora of CMOS opamps that'll fit your needs.

CMOS has even become pretty good for relatively low noise applications.

--
Thanks,
Fred.