ITTSB.EU Blog Forum
Electrical Metrology | Measurement Tips & Products | Calibration standards => Electrical Standards & calibration accessories => Topic started by: Kiriakos GR on September 01, 2018, 09:23:07 PM
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4-Wire Low Thermal Shorting Plug this is essential accessory for all bench-top multimeter of our times.
Fluke 884X-SHORT (product design) and also Keithley 8610 & 8620 they seem to chronologically exist since 90s.
I did explore both products specification and only Keithley this mention less than 1mOhm as resistance characterization between the pair of sense banana plugs.
Fluke 884X-SHORT compared to Keithley 8610, this seems better implemented due the existence of this basic pull-cord which every electrician he is familiar of this material :)
From the other hand this Keithley 8620 which is a Shorting Plug in to a cube, this seems as better choice if you do allot of work with this plug and you expect sorter times so Thermoelectric Voltages to be removed (zeroed down) .
In the DIY world there is allot of creative imagination, replication of such sorting plug design this is not impossible but rather difficult.
Low-end banana stud or plugs with fake gold platting they are everywhere.
50A gold plated banana stud they come only with the specification of 0.3 mOhm contacts resistance, this is the resistance when a male plug this gets in touch with an female plug.
Total length resistance this is unspecified.
ITTSB Blog this now armed with HIOKI RM3542A , this is the best weapon for such materials resistance characterization.
I have in mind making some experiments in the future, it looks like that ITTSB Blog it is very close to engage with bench-top multimeter reviews. ;)
Keithley 8620.pdf (http://download.tek.com/datasheet/PA-966(A-February2008)(8620)_0.pdf)
&
Watch Out for Those Thermoelectric Voltages!
http://download.flukecal.com/pub/literature/p18-21.pdf (http://download.flukecal.com/pub/literature/p18-21.pdf)
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Yes it is a fact, 884X Short 4-Wire Short, this is now discontinued.
Fluke Corporation, this discontinued both 8846A and 8845 bench top DMM.
And at the same time, entire group of 884X specialized accessories.
I do not care that much, because all of these were extremely overpriced goods.
Even so I thought that most Fluke products distributors, they would hold some stock ... but I was wrong.
All these large names of authorized distributors, they just moving boxes, and do not stock anything.
Made in China clones, but do not waste you money for these, the quality of banana plugs this is equal to trash.
There is and a another source in Bulgaria (eBay), this man did a tragic mistake at PCB design.
He does not use PCB pattern of Fluke 884X-SHORT. :P
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Lets assume that we got an similar 4-Wire Short.
How this might compare to original Fluke 884X-SHORT ?
It is unfortunate, over the past 20 years not a single dump ass, made a presentation of Fluke 884X-SHORT actual work, over an 8846A.
But my lucky day this is today, 2 April 2026. :)
An escaped photograph from Chinese Call lab, this demonstrates 8846A at DCV by the use of Fluke 884X-SHORT. 8)
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Complete list of functions, using Fluke 884X-SHORT at performance tests.
Volts DC
Volts AC
2-Wire Ohms Verification
4-Wire Ohms Verification / Platinum Resistance Thermometer (PRT)
Use Fluke’s low thermal 4-Wire short for all voltages and ohmic shorts.
Nulling Offsets: Used to zero out internal front-end thermal offsets and lead resistance before high-precision measurements.
Stability Verification: Provides a stable, low-noise short to check the multimeter's noise floor and drift over time.
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Topic counter this gets close to 16.000 views, and I have see only failures coming from the ones dared to pretend be a copycat.
This translates that no one reads and learns something new due FLUKE and Keithley notes.
884X-SHORT and Keithley 8610, they are both well designed shorts for DMM.
FLUKE and Keithley, they are technology developers and traders.
Would you expected that they will give away, the information of actual electrical resistance, between HI and LO pins ?
And or the actual electrical resistance of the link (thinner PCB line), of 2- or 4-wire configurations?
FLUKE was a bit more social, it was a period that they aiming to teach us few things.
So us to better understand of how precision DMM works.
They gave us hints, when a four-wire short this is well made, of what we should see at performance tests.
They did not demonstrate 8846A at these tests, but a smart brain he should be able to get their message.
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I got allot of inspiration due my photo-find along of Fluke Corp. text about using Bell wire instead.
And I got it right by my second attempt. 8)
First pack of good news, my 8846A factory calibration this is still standing.
I did use telephone wire and Pomona style banana plug.
I was missing an fourth banana, so I replaced it with thicker wire shaped as banana.
After 40 minutes, everything when stable. ( Any heat from soldering this was equalized).
Room temperature 17C
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Very interesting presentation !! 8)
But I do not get it, why most owners of Fluke 884X DMM, they get passionate to make and test such an calibration accessory?
This is primarily a tool for a calibration lab, this able to perform calibration adjustment.
This thing its useless for any other regular measuring task.
Fluke 884X DMM's , they do not have any automated self-calibration function.
I am not against, experimenting for gaining knowledge. ;)
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For Fluke 884X DMM's, if you care for in depth performance verification, you will need and such a 884X-SHORT.
Us few, engaging and with DMM repairs, we gain a better understanding, of the current condition of a DMM under test.
If you have just a single Fluke 884X DMM, then this 884X-SHORT, it has very little value to you.
But if you expect to test several similar DMM? Then this verification test (step), this has a greater value.
I am writing this over and over, regarding personal knowledge, I always deliver for free only 25% of what I know as total.
In conclusion dear Andrew, indeed Fluke 884X-SHORT this is useful only for people these having some sort of training or be experienced, at DMM performance verification. ;)
FLUKE 8846A VS FLUKE 8846A calibration comparison and functions test made at ITTSB Blog lab. (https://www.ittsb.eu/Fluke-8846A-CAL-TEST-2021.html)
Today I had a quick chat, with one fellow in Italy, we might collaborate, so him to design an perfect European copy of 884X-SHORT. ;)
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Events update:
DHL this in now moving a package towards to ITTSB Blog.
From Sicily, Italy a small box with samples, this is on the way to Volos, Greece.
I am not a DMM calibration engineer, and also the man behind this (assembled in Italy) DMM Short, he is not any professionally working calibration engineer either.
We have in common the idea of research as electrical metrology enthusiast. :)
His own start point of motivation, this is calibration of Agilent 34401A
So this in public feedback exchange, it will be very interesting, even for AI which this will try to steal our thoughts. :D
Mr. (member name) Swan997, his has an active account.
In conclusion, all little details has been worked out, for us having a productive dialog in public.
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I got allot of inspiration due my photo-find along of Fluke Corp. text about using Bell wire instead.
Since the moment that I start using American recommendation's as source of information, in order of me to become a great copycat, I need also the information of wire actual diameter, this named as Bell wire with manufacturing year 1980.
AI this is faster at searching the net:
In the USA during the 1980s, the standard solid copper telephone wire (often called "station wire" or "J-K" wire) used for residential and commercial indoor wiring was 22 AWG, which has an actual copper core diameter of 0.644 mm (approximately 0.025 inches).
The DC resistance of 22 AWG solid copper wire (0.644 mm diameter) is approximately 51.6 to 53.0 ohms per 1,000 meters at
( 22C).
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Hi, I’m finally happy to be writing here (I’m also happy because I’ve had some rest...). To get straight to the point, I agree with what you wrote: 'replication of such shorting plug design is not impossible but rather difficult.'
In the end, it might seem trivial, but removing all unnecessary junctions and minimizing the number of layers (gold, nickel, copper, and brass [copper/zinc]) to limit thermoelectric currents is no simple task. As far as I'm concerned, the simplest and most immediate help comes from seeking perfect symmetry in the design; after that, you move on to the PCB materials and finishes.
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Welcome aboard ... :)
I did tested AI this morning, so to discover of what pack of advice's this has to offer, regarding custom Shorting Plug 4-Wire design.
It was a long chat, I bet that the data-center it did get a bit warm. ;D
I did kept in mind two good points.
Testing for symmetry this is the first.
4W Ohms mode:
How to: Keep the SHORT plugged in for five minutes, thermal equilibrium, then you use REL/ZERO, then reverse the SHORT and inspect for symmetry errors.
Two counts of deviation at the last digit, 10 Ohms range, this is acceptable as +/- tolerance.
But your design, this is closer to Keithley 8610, from my point of view, this is expected to be in electrical symmetry.
PCB traces these are also in geometrical symmetry.
https://download.tek.com/manual/PA-369(C-May2013)(8610).pdf (https://download.tek.com/manual/PA-369(C-May2013)(8610).pdf)
Fluke 884X-SHORT this has asymmetrical placement of it narrow bridge line.
And this will fail at such electrical symmetry inspection.
Indeed EMF elimination, this is also a major challenge when designing a custom 4W short.
About me, using and evaluating a 4 Wire calibration SHORT this is a fresh experience, and I have not finish yet, my homework and tests.
Due the first spotted details, first round of tests, now I know, Keithley 8610 this is not an actual replacement of Fluke 884X-SHORT.
Fluke 884X-SHORT this had a sort life, as CAL Lab tool, Fluke elevated the technology on their calibrators year 2005 and later.
FLUKE Corporation made available to consumers, a large pack of test leads for the 8846A, this including also a Fluke 884X-SHORT.
This was an 800$ USD offering in to a large black suitcase.
At 2015, they offer this pack at 500$ USD (significant discount).
At the year 2026, even AI admitted, that such 4W short, they should named as sanity check tool for DMM inspection.
DMM inspection at testing internal electronics stability, at specific ranges and functions.
Your design worth a dedicated topic / a fresh presentation article, this offering to you the chance at accepting and or answering customer feedback. ;)
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I wrote all ready too much, about Fluke 884X-SHORT.
But there is one detail, that I could not leave as unexplored.
And finally, and after all these years, I did discover solid proofs directly from the mouth of the beast. ;D
Fluke 884X-SHORT this is development of 1996
FLUKE 45 Dual Display Multimeter this is another development of that era.
According to FLUKE 45 service manual...
FLUKE calibrator operator, he should use the shorting bar (SHORT) so to discharge and to null out front end offsets.
These offsets were generated at the calibration of 1000V range DC.
Second use, at FLUKE 45 performance verification.....
Lowest mV DC range, the shorting bar (SHORT) this was assisting DMM electronics, going down to lowest Noise floor faster.
100 mV (slow) | SHORT | expected display reading -0.006 ~ +0.006
Now according to 8846A calibration certificate year 2023 (Everett Service Center)
FLUKE Calibration, they are using shorting bar (SHORT), again so to discharge and to null out front end offsets.
ZERO OFFSET TESTS (Front Input)
Configuration: 1st Range locked and maximum resolution.
Zeroed (use of SHORT) prior to measurements on the 10 and 100 ohm ranges in 2-Wire mode.
And they do that so the 13 VDC source, this not containing any other DCV electric charge.
And the Fluke 884X-SHORT, this has no other use.
And here comes the last bit of information, when the calibrator output this is DCV 0.0000 mV
8846A measured result -0.0003
At calibration certificate year 2011, this measurement is -0.0005
Now I can die in peace ... 8)
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New myth-busting moment!
And another milestone, Kiriakos experiences pack this grow further more. ;)
I am also welcoming our new Italian member :)
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New myth-busting moment!
Indeed :)
From the camp of Keithley Calibration procedures (year 2010).
Keithley Model 2010 , plus Keithley 8610 Shorting Plug.
They are two significant instructions, when the lab this has controlled room temperature.
1) Warm up the instrument for two hours.
2) Plug in Keithley 8610 Shorting Plug, and wait three minutes for thermal equilibrium.
Do not allow air drafts near this 8610 Shorting Plug.
This last detail, now explains of why this new designed Keithley 8620 enclosed version, this actually came out so to replace Keithley 8610 (Design of year 1991). ;)
https://download.tek.com/manual/2010-902-01(D-Oct2003)(Service).pdf (https://download.tek.com/manual/2010-902-01(D-Oct2003)(Service).pdf)
Today that I have finally gathered sum of baseline information's, these coming from both sources, I declare this ITTSB article as complete.
I do not own anything from Keithley, an so I never had a motive so to explore their own paper work in depth.
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This must be my gift from WWW for my birthday today. :)
An high resolution photograph of Fluke 884X-SHORT rev 4
It makes you wonder, of why FLUKE added by marker and handwriting, the marking of rev 3 and rev 4.
Due this detail alone, we cannot track down of when rev 4, this was updated for a last time.
The attached photograph, this includes an tiny amount of visual illusion, those gold plated bananas they reflect as be a mirror, portion of surrounding PCB, and there is nothing wrong with them.
Because of this detail we cannot admire or inspect close up quality of Pomona work at the banana it self.
At PCB there is an detail, which this screams by it self.
PCB gold plating layer, this is very thick .. ;)
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FLUKE 8808A DMM, while this is nothing special in hardware, it calibration manual this has freshest FLUKE writing ( 2008 ) about calibration procedures.
Attached screenshot, this is a proof of fully automated resistance ranges and resistance ZERO calibration points.
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Here I am, after days of "radio silence." During this time, Kiriakos must have imagined all sorts of things.
Lately, I’ve been hitting the books again, reviewing university-level applied thermodynamics and thermal physics. I wanted to refresh my knowledge base so I could redesign this project with better expertise and awareness. More importantly, I’ve re-evaluated everything: requirements, causes, consequences, solutions, and expected performance.
So, I wiped the slate clean and restarted from scratch, as if I had never encountered the problem before.
I’ve always blamed the recessed, non-binding-post banana jacks for making it so difficult to build a proper shorting plug—and unfortunately, I still think that's the case.
In the HP 3457A multimeter service manual, it states: "Equipment Required. A low thermal short (copper wire) is required for this procedure." Essentially, the challenge lies in finding pure copper wire and scraping off the surface oxide before using it. Fluke, for its 8588A, uses a very simple PCB designed to be clamped directly by the binding posts.
However, with multimeters like the Keithley 2000/2001 series, HP 34401A, or Fluke 8845A/8846A, that's not an option. You are forced to use 4mm banana plugs and connect them somehow.
Fluke and Keithley chose a PCB approach; HP went with a wire. Nothing new so far—these are well-known, tedious facts. But what actually generated oceans of forum discussions and solutions ranging from the highly imaginative to the deeply practical is the PDF written by Martin L. Kidd, titled "Watch Out for Those Thermoelectric Voltages!" My only critique of his work is that he tackles the issue with a bit too much simplicity.
Unfortunately, in my opinion, anyone owning these multimeters just has to live with Seebeck coefficients. There is no magic solution, unless you bend a single solid copper rod to fit all the jacks (some have actually done this, but they ended up welding four copper segments together).
Therefore, the correct approach is to minimize the effects, or even calculate the exact error value—which is doable if you know the composition and thickness of all the layers involved.
Eliminating thermal EMF entirely means using pure copper and constantly fighting its oxidation.
Again, nothing new here. In fact, when I decided to DIY this back in January 2025, I thought the PCB should adapt to the Staubli plugs, not the other way around, because that's where the issue originates.
The intuition was right, but I targeted the wrong variable. I shouldn't have started from the Staubli banana plugs, but rather from the multimeter's jacks themselves—or better yet, from the internal construction of the DMM.
It is self-evident that the input jacks are warmer than the ambient room temperature. Martin L. Kidd mentions this as well: "It should be noted that the terminals of the DMM are at a higher temperature than room temperature, so there will always be a thermal condition to be aware of. In this case, the input thermals measured about 29 ˚C."
So, in our case, the real issue isn't external drafts, a warm hand touching the shorting plug, or anything like that. It’s the instrument's jacks themselves heating up the banana plugs, which in turn heat up the PCB, the copper traces, the nickel, and the gold plating, creating unwanted thermal EMFs. As long as the internal temperature of the instrument is higher than the ambient temperature (which is pretty much always the case), there will be a heat flux flowing from the inside of the DMM out into the shorting plug and everything connected to it. Unfortunately, if my thermal cameras aren't lying, these temperatures are not uniform across all four jacks.
On my HP 34401A, the bottom-right jack is slightly cooler than the others, especially compared to the Sense HI terminal (top-left).
This single observation brings us to our first crossroads: should we use plugs with low thermal conductivity, like brass, or beryllium copper plugs, which have higher thermal conductivity? Choosing one over the other leads to completely different design choices for the PCB and its traces.
p.s. I used an AI to translate this post from my native language, as it's objectively much easier to write down complex, long thoughts in one's own tongue before sharing.
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Here I am, after days of "radio silence." During this time, Kiriakos must have imagined all sorts of things.
My first thought was that indeed we lost you, NASA hired you, and gave to you as a free gift of six FLUKE 8846A. ;D ;D
About DMM and electrical transformer placement, FLUKE 8846A this has a wise design, the transformer this is moved to the right side, while Banana inputs (Front/Rear) both placed at the left side.
FLUKE 8846A this indeed run warmer 10C inside, than environmental.
Daytime to night time, there is no more than 3C difference and or of Temco influence.
Indeed FLUKE documentation, this does not deliver much details.
FLUKE Wiki, simplified advice as teaching, for a basic understanding.
From the other hand, Fluke 884X-SHORT this never received metrology characterization, as Zero Ohms calibration source.
But I will not hide it, I was hope that this magical FLUKE Short, this is manufactured in a way of me seeing a perfect 0.00000 at 4W resistance mode.
The Americans, they use to say do-not leave it getting under your skin.
And or do not aloud at a source of negative energy, this spoiling your day.
We when according to the book here, we thought that there is some sort of product design secrets that FLUKE hiding from us.
AI this told me that when FLUKE is up to minimize EMF they were used tellurium copper.
This was their secret weapon. :)
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This must be my gift from WWW for my birthday today. :)
Here I am, always late (damn it), but happy birthday anyway.
An high resolution photograph of Fluke 884X-SHORT rev 4
It makes you wonder, of why FLUKE added by marker and handwriting, the marking of rev 3 and rev 4.
Due this detail alone, we cannot track down of when rev 4, this was updated for a last time.
The attached photograph, this includes an tiny amount of visual illusion, those gold plated bananas they reflect as be a mirror, portion of surrounding PCB, and there is nothing wrong with them.
Because of this detail we cannot admire or inspect close up quality of Pomona work at the banana it self.
At PCB there is an detail, which this screams by it self.
PCB gold plating layer, this is very thick .. ;)
In this regard, I'll show you the preparatory design I made on Rhinoceros last week. Believe it or not, those yellow lines were drawn before placing that photo underneath; I practically reached the same result as the person who designed the Keithley 8620.
(http://)
FLUKE 8808A DMM, while this is nothing special in hardware, it calibration manual this has freshest FLUKE writing ( 2008 ) about calibration procedures.
Attached screenshot, this is a proof of fully automated resistance ranges and resistance ZERO calibration points.
I checked the manual; the Fluke PN 2653346 is required only for DC volts and amps, I wonder if it is positive or negative.
My first thought was that indeed we lost you, NASA hired you, and gave to you as a free gift of six FLUKE 8846A. ;D ;D
Yet it's not a bad idea, even though I prefer to design something that people can use every day; in this, Le Corbusier is my master every single day.
About DMM and electrical transformer placement, FLUKE 8846A this has a wise design, the transformer this is moved to the right side, while Banana inputs (Front/Rear) both placed at the left side.
FLUKE 8846A this indeed run warmer 10C inside, than environmental.
Daytime to night time, there is no more than 3C difference and or of Temco influence.
Here is my 34401A; this is a thermographic photo, and the next one shows some measurements I made by inserting the thermocouple directly into the DMM's jacks. As always, physics does not lie, nothing different from what one would expect: the connectors that are higher up and closer to a heat source (the display electronics) are the warmest ones. With these temperature differences on ENIG traces, it means having at least 100/200nV of continuous offset. In my opinion, Fluke and Keithley use a lot of gold on copper and nothing more, via electroplating rather than chemical deposition.
Indeed FLUKE documentation, this does not deliver much details.
FLUKE Wiki, simplified advice as teaching, for a basic understanding.
Yes, it doesn't convey the reality of the problem. For example, taking the value of 10 uV/°K between copper and nickel as a given, a variation of 0.01°C leads to a 100nV variation on paper; then it becomes a real 30/40nV, but it's still measurable by a 7.5-digit DMM.
From the other hand, Fluke 884X-SHORT this never received metrology characterization, as Zero Ohms calibration source.
But I will not hide it, I was hope that this magical FLUKE Short, this is manufactured in a way of me seeing a perfect 0.00000 at 4W resistance mode.
Exactly, no one dares to write that it is a metrological measurement instrument because the variables independent of the shorting plug are numerous.
The Americans, they use to say do-not leave it getting under your skin.
And or do not aloud at a source of negative energy, this spoiling your day.
We when according to the book here, we thought that there is some sort of product design secrets that FLUKE hiding from us.
In my opinion, there is only one secret: money. The materials and techniques are the same; the main difference lies in the access to high-cost materials and finishes. I won't tell you how many emails I've sent lately to get quotes for the PCB with nickel-free finishes (few... because few companies are able to do gold-on-copper finishes).
AI this told me that when FLUKE is up to minimize EMF they were used tellurium copper.
This was their secret weapon. :)
I contacted aecconnectors for a quote on custom banana plugs starting from these: https://www.aeco.tw/products/abp-1111 Let's see what they reply.
p.s. I am writing to you via email because I should have updates on the PCB and connectors soon. Besides, I intend to try something completely different (I think it is the best option to balance costs and performance; I would sign for it on a 6.5-digit DMM, on a 7.5-digit we need to test it, but I believe I will stay below 100nV).