[volt-nuts] What's All This Low Thermal EMF Test Lead Stuff?

pa4tim at gmail.com pa4tim at gmail.com
Wed Aug 20 02:23:15 EDT 2014


About the Keithley mentioned by stephen, It is a free download but they have a free paper version too.  I have a picture of it on my site. Scroll down until you see a red book. http://www.pa4tim.nl/?p=2899 


Fred, pa4tim








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Van: Stephen Grady
Verzonden: ‎woensdag‎ ‎20‎ ‎augustus‎ ‎2014 ‎06‎:‎31
Aan: volt-nuts





Fellow Volt-Nuts

If I can put a recommendation in for an Australian publication, NMI
Australia runs courses in Electrical Measurements and publishes a monograph
of the course.

Monograph 6 The Measurement of Electrical Quantities (2009, third edition)

Ilya Budovsky et al, 140 pp ($125, overseas $140)
The monograph describes principles and techniques of the measurement of
electrical quantities (direct and alternating voltage, direct and
alternating current, resistance and high voltage), particularly with the use
of digital multimeters (DMMs) and calibrators. The emphasis is on the
techniques of reliable measurement and this necessarily involves a detailed
discussion of the systematic errors that affect the measurement of
electrical quantities as well as the principles of operation of DMMs and
calibrators. Also discussed is the calibration of DMMs and the calculation
of the uncertainty of calibration. The monograph gives an introduction to
the primary standards of electrical quantities.

There is a good section on guarding in this publication; the different types
and correct/incorrect methods of guarding.

It can be ordered through
http://measurement.gov.au/Publications/Pages/Monographs.aspx there is a link
at the top to download a pdf order form.

If you are looking for a free publication I like the Keithley publication
and I vaguely remember Hewlett Packard (as they were then) in the 1970's or
1980's publishing an application note on this subject (a search through the
HP ap note archive may show which one) or Keysight  may still have it on
their website.

Kind Regards,

Stephen Grady
Sydney, Australia

-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
Behalf Of Stan Katz
Sent: Wednesday, 20 August 2014 9:35 AM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] What's All This Low Thermal EMF Test Lead Stuff?

You are on the money that guarding/shielding are sadly neglected as
subjects, in their own right. Posts in this group consist primarily of
reports of guard leakage in member instruments, and repair details.
Discussion of proper lash ups of cal. instruments to home built devices, or
even work prototypes, would be very welcome by me. I have read Analog
Devices AN-347, but a tutorial with problems that the student must complete
the lash ups for, would give me a better idea if I've grasped the subject
matter. There are two text books mentioned at the end of AN-347, one by
Morrison, the other by Ott. Any suggestion as to which to buy? The latest
texts by these authors are pricey, so that's why I'd like to pick just one.


On Tue, Aug 19, 2014 at 3:37 AM, <acbern at gmx.de> wrote:

> generally I think, and at least for your gear, if you use copper plugs 
> of some type and even solder the wires, thats perfectly fine.
> also for a 3458a, and after proper temp stabilization after connecting 
> the cables (5min) which you always need, these are fine, have not 
> measrured any difference to crimped cables. also the type of cable 
> plating (tin/silver..) does not make much difference.
> there were many discussions over time, but all the cadmium solder and 
> non plated copper type debates are not making much sense down to the 
> 3458a level.
> I have not done comparison tests with nanovolt meters, as mine have 
> fixed cables, so no option to change them without destroying them, but 
> note that e.g. the 182 nanovolt meter has a mil type plug (no special
contacts).
> sources of error are also things like where to connect the guard to, 
> these often make a much bigger difference (I have seen these many 
> times, causing voltage differences of several uV depending where in 
> the setup you connected the guard, while otherwise the measurement was 
> perfectly stable), and I bet while people put a lot of effort into the 
> emf discussion, the guard issue is more often causing errors in 
> measurements in real life. and thats just one example of additional causes
of errors.
> cheers
>
> > Gesendet: Dienstag, 19. August 2014 um 06:07 Uhr
> > Von: "Stan Katz" <stan.katz.hk at gmail.com>
> > An: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> > Betreff: [volt-nuts] What's All This Low Thermal EMF Test Lead Stuff?
> >
> > I'm a self described volt-nut-near-beer. I don't own a 732A/B, or an 
> > HP3458. I do own HP3456 DMMs that are at the top of my 
> > instrumentation pecking order.  I have all the necessary gear to 
> > calibrate these DMMs according to ancient HP documentation. At the 
> > top of my cal. chain is the 731B, called out in HP3456 original 
> > documentation.  This hierarchy places me in the near-beer, or junior 
> > member status of the group. I look forward to being educated, and/or 
> > corrected on my understanding of the use of
> test
> > leads with precision instrumentation.
> >
> >  I don't find much ancient HP documentation on test leads. The only 
> > recommendations in the era of the 3456 back to the 1960's is to use 
> > as thick a solid lead of pure copper wire as you can find, and 
> > insert the
> wire
> > into the drill hole on the banana terminal. If the copper is pure, 
> > and
> has
> > been properly cleaned, the thermal emf's on both identical length 
> > leads should all be balanced, and cancel out. In any case, pure 
> > copper-copper connections generate the lowest thermal emf. I  will 
> > agree that
> manhandling
> > 16 gauge solid wire can be very inconvenient.
> >
> >  The path I have taken recently is to order Nakamichi gold over 
> > copper stereo banana plugs for my connections ( I deal in low 
> > voltage work exclusively), as well as gold plated spade lugs to go 
> > under the banana screw-downs. ( My budget ruled out gold over 
> > beryllium copper Pomona
> brand
> > spades. )  I will then experiment between the two connector types. 
> > As for connections, it seems to me the best course is just to screw 
> > down the banana plugs, or in the case of the spades, just crimp. 
> > I'll wing it on
> the
> > crimping, and see if simple tools can perform adequately. I would 
> > avoid solder, since how can one form identical topological spots of 
> > solder on every connection, deposited at the exact same place on 
> > each connection,
> and
> > ensure the exact same weight of solder, to the microgram, on each 
> > connection. Since my modus operandi is to aim for balanced emfs, I 
> > think solder is out. Of course, if one wishes to risk one's health, 
> > and that of the family, one can track down a source of cadmium, and 
> > mix up a lot of
> low
> > thermal emf solder (cadmium solder is banned in the US, and 
> > EU)...not for me.
> >
> > Don't worry, I won't be using tin plated wire, I managed to pick up 
> > a
> spool
> > of silver plated 16 gauge wire for my investigations.  Am I on some 
> > other planet for choosing the balanced thermal emf approach for 
> > precision test lead applications, as opposed to going to great 
> > lengths to eliminate
> every
> > trace of emf?
> >
> > Please forgive me if these emf discussions have been between 
> > engineers working outdoors in the oil fields of North Dakota, or out 
> > on a North Sea drilling platform. In that case, go for all the super 
> > low emf techniques you can lay your hands on.
> >
> > Good Luck,
> > Stan
> > _______________________________________________
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> > and follow the instructions there.
> >
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