cost of measuring picoamps

[Allan Adler]

I'm looking at a book by Gilardini on slow (on the order of 0.1 eV)
electrons in gases. He mentions that the dc currents one has to measure
in such a situation are on the order of between 10^-11 and 10^-13 amps.
I'm just wondering how much it costs to be able to measure such small
currents, i.e. the equipment to do the measurements.

 

[Homer J Simpson]

I'm looking at a book by Gilardini on slow (on the order of 0.1 eV)
electrons in gases. He mentions that the dc currents one has to measure
in such a situation are on the order of between 10^-11 and 10^-13 amps.
I'm just wondering how much it costs to be able to measure such small
currents, i.e. the equipment to do the measurements.

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

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

 

[greysky]

I'm looking at a book by Gilardini on slow (on the order of 0.1 eV)
electrons in gases. He mentions that the dc currents one has to measure
in such a situation are on the order of between 10^-11 and 10^-13 amps.
I'm just wondering how much it costs to be able to measure such small
currents, i.e. the equipment to do the measurements.
--
Ignorantly,
Allan Adler <[email protected]>
* 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.

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

 

[Allan Adler]

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
http://www.winfordeng.com 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.

 

[Allan Adler]

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

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?

 

[Boris Mohar]

I'm looking at a book by Gilardini on slow (on the order of 0.1 eV)
electrons in gases. He mentions that the dc currents one has to measure
in such a situation are on the order of between 10^-11 and 10^-13 amps.
I'm just wondering how much it costs to be able to measure such small
currents, i.e. the equipment to do the measurements.

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) http://www.viatrack.ca

void _-void-_ in the obvious place

 

[Fred Abse]

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?

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.

 

[Homer J Simpson]

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.

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.

 

[Allan Adler]

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

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

 

[Allan Adler]

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.

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.

 

[Boris Mohar]

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

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) http://www.viatrack.ca

void _-void-_ in the obvious place

 

[Homer J Simpson]

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.

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).

 

[Allan Adler]

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.

Thanks for the explanation.

 

[Allan Adler]

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).

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.

 

[Homer J Simpson]

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.

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.

 

[Allan Adler]

I'm trying to follow up on the suggestion of
Boris Mohar <[email protected]>
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?

 

[Allan Adler]

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.

 

[Wim Lewis]

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?

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).

 

[Fred Bartoli]

Allan Adler a écrit :

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.

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.

 

[Paul Rako]

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).

The LMP2012 is a chopper amp and would be unsuitable for
measuring picoamperes. Maybe the LMC6484 but the real
deal is that the LMC6001 is just a hand-selected LMC660.
Any LMC part would be OK as well as JFET parts like the
LM411. Input bias doubles with every 10 deg C in temp
so keep it cool. I wrote Paul Grohe, National Semi
applications guru and he said:

==================
"The 6001 is just guaranteed to be less than 20fA due
to a special test. They are no longer hand-tested
(that was the old metal can version), but they are
still screened with the long-term test. That is why
they are so expensive - long test time and "value added".

"N" suffixes are the old DIP's - which we do not make
anymore, except for specific parts where there is still
huge DIP volume. "M" suffixes are the SOIC package. The
"A" and "B" suffixes are the offset grade (A=better).
The "I" means industrial temp range.

Otherwise, the LMC660/662 is still the king of the cheap,
low Ibias CMOS op amps. Use the second channel of the 662,
mid VCM, and you will be in the low fA's. The older devices
with the 500V HBM ESD rating have the lowest leakage.

The LMP2011 is a CMOS device, but the "chopper" CMOS input
switches cause charge transient spikes on the inputs, which
will disturb a very high-impedance circuit. This can happen
with any chopper and is not specific to the 2011.
======================

There you have it from the source, and Paul noted there is
link in the upper right of National's page to go back to HTML
tables.