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1
These days I am exploring entire market and makers of   6 1/2 benchtop multimeter.
 
M3500A  DMM this one it is much less know in Europe because for a long time Taiwanese ODM they were selling this product to American brands and them selling it overpriced with end result vast majority of consumers never touched it. 

Now lets get back in time and start from the begging, first marketing trace of M3500A DMM this made by PICOTEST Corporation and according internet traces, first one this discovered at October 2006. Asian web-page.

Two years later ARRAY.sh  in Taiwan also appears as factory distributing this model.
While January of 2018 ARRAY brand prints it first product flyer, general manager Mr. Hawk Shang, he was received final documents of product declaration according to European standards at  13 August 2009,  therefore since then and after they could export their product.

What it does bother me this is the FACT that in the past 12 years neither of them demonstrated passion for perfection so to build a nice website, this also offering the ability so international customers to be able to order a single spare part for this multimeter. 
 
M3500A it was about to be forgotten even in Asia, but it competitor HP/Agilent  34401A this become EOL at 2016 and M3500A resurrected from the dead as compatible product design which it can replace dead 34401A these working in specific industrial test systems.

Regarding vast majority of consumers in west world M3500A this is invisible, no one tested it, no one made a review of it and no one take it apart.
 
From the other hand my research revealed that this product since day one was fully documented and service manual was freely available with all technical details other than calibration unlock password.

Within 2012  (five years after production) in a Chinese forum users starts talking about it, and major complains are two, menu system has some of complexity and internal voltage reference ( APEX  VRE310 ) this is not that immune to room temperature changes caused at night and within  24 hours operation.
In simple English while M3500A this is somewhat superior to 34401A in measuring speed, when it comes down to electrical metrology comparisons and testing of voltage accuracy, old 34401A with internal Vref LM199/LM399 (By Linear Technology)  this has superior stability and repeatability (warranted by internal heater).

Personally I did build my own 10V voltage reference standard by selecting LT1021-10 (By Linear Technology), direct comparison of the three:  LM399 – VRE310 and LT1021-10, it makes clear that LT1021-10 it is the winner while all three are quit similar.
LT1021-10 this is just a bit clean of Peak to Peak noise compared to LM399, and immune to drift from 2 Celsius up to 100 Celsius.


Begging of 2019 I did politely challenge both PICOTEST and ARRAY so ITTSB Blog to receive a latest produced product sample, this inducing matured firmware and PCB revision, for a true evaluation and product review of M3500A in European terrain. 
In case of refusal from their end, this automatically translates that neither ITTSB Blog will ever deliver a positive recommendation to Blog visitors about getting one.
2
Glass of water as measuring object really works well,  but you must be fast at taking your measurement by a multimeter this be powered (warmup) for 15 minutes at least.

In this experiment as soon the class inserted in door and thermocouple inserted  to it,  multimeter measured right away  3.5C.
Unfortunately for such a measurement process just a minute later temperate started to gain influence from indoor temperature.

Even so I do classify this work around as highly successful method    8) about measuring Low Temperature by a multimeter and a thermocouple.
Alternative option this is buying a ten meters long thermocouple, but over all this is not practical idea because you will have to find or drill a hole, so the wire to pass from in-door to outdoor.

Therefore my very own suggestion using a glass of water this is much preferred one, but be quick  ;D ;D     
3
Two Decembers later the same thought bothered me again, and this is what trickery to do for measuring temperature of a cold night when external temperature this is at 1.5 Celsius or about there?

Handheld multimeter lucking cold junction adjustment for thermocouple compensation and practically this is a dead end.
But the answer and solution came to me by thinking that Zero Celsius calibration this is equal to a K type thermocouple shoved in to the snow.  :)

Therefore workaround suggested this is leaving outside a glass of water for an hour and then measure water temperature indoor .... this workaround will increase measuring accuracy because of all reasons mentioned at my post above.

Second interesting testing by shoving a thermocouple in to the snow, this is inspection of multimeter calibration.
Today I do own three U1272A,  and Zero Celsius calibration after testing all three, it is measured at +/- 1 Celsius.       
First meter measurement:  minus 0,5
Second meter measurement: 0,0
Third meter measurement:  Plus 1,0 Celsius 

Naturally any measured difference when comparing identical multimeter, this having to do with precision of calibration adjustment when this was performed at factory or elsewhere.
From the other hand any calibration report this serves and the purpose of consultant for us when we seek ultimate measuring accuracy, in a way we should mathematically compensate any detected deviation marked at calibration report from our own measurement.       
4
EURAMET Newsletter Issue 14 is now available.

Take a look and ...

 Learn how the International System of Units has been overhauled in an historic vote
 See what is behind EURAMET's new European Metrology Networks
 Find out what is on the agenda of next year's International Metrology Conference
 Get to know new EURAMET officials including three new Technical Committee Chairs
  And a lot more ...


Enjoy reading!
https://www.euramet.org/publications-media-centre/euramet-newsletter/
5
Fate or not, first portable calibrator which I purchase as used for my tests at ITTSB Blog  this is TIME ELECTRONICS LTD - MICRO CAL 1030 Precision analogue voltage current DC source (9-2010).
Product datasheet mentioning an AC power block which I never got, because interesting enough this was optional accessory.

Six years later (10/2016) ITTSB Blog established direct communication with Time Electronics UK (brand) and headquarters.
TE marketing team acknowledged the work of ITTSB Blog over the years and it did offer to me modern samples of their products for a product review.
And this is how one modern 1048 Voltage Current Loop calibrator with digital screen and digital controls is now property of my Blog.

Unfortunately the history repeated it self once more time, AC power block (12VDC) for 1048 calibrator this was again optional.
Due the fact that both calibrators are quite useful in my hands, for some time I was thinking to make then both to operate with DCV power supply instead using batteries.

Few months ago one friend of my, he made me a gift and this is analog blood pressure device of 80s.
By removing the analogue meter from it housing, I made the discovery that 1048 portable calibrator this has exact dimensions!
My next thought was to add on-board power supply this delivering 12V for the 1048 and also 9V for MICRO CAL 1030, so to be able to use both simultaneously.
Hart of the power supply become one regular transformer at 18V AC 700mA. Rectifier Bridge and filter delivers 22V peak which feed LM7812 this mounted over a huge aluminum plate.
Output of LM7812 after a second filter this is delivered to a power plug and also to a LM7809 this act as power supply for MICRO CAL 1030.
While total power supply design this is quite simple, finalizing of this project it required allot of work and time, everything it should fit in the dimensions’ of the specific housing (project box), and I had to do several changes and modifications.

The outcome this is now very impressive and unique as product design worldwide.
They say one picture equals 1000 words, I did add much more than one pictures.
I feel extremely proud about this project, because now long term calibration stability tests are now possible, especially for tests that I am going to do near soon at bench top multimeters.
Within 2019, ITTSB blog will receive several samples for a product review.
6
Interesting question  :) 

From my point of view, we cannot deny high digits resolution because our measuring quantity cannot be that stable at 5 ppm lowest value.

My own question which no one is willing to answer this is :  Why there is no modern made, faster, highly accurate and cheaper 8 ½ digits meters in the market at 2018 ?
Why the supposed calibration grade DMM they are all made 20 years ago ?

While I do wish owning a meter with one million counts resolution for my Blog, the market it is now twisted in a way that even me I am 100% confused of which direction to follow.
For now I am voting in favor of patience, it is possible something fresh to shown in 2019 ...   

 
7
Therefore in a multimeter of 8 ½ digits with one million counts resolution, we should now ignore from our measurement a roughly sum of 6 ppm of changes, and justify this quantity as acceptable variation caused due latest Low-Thermal capabilities of the materials that we use at 2019 on planet earth.
According my understanding in the future we could possibly witness such a 6 ppm unavoidable Low-thermal deviation this to now listed in the column of measuring uncertainty in a high-end multimeter calibration report.

I will never be buyer of a multimeter at 8 ½ digits, but I do get the point that you are talking about DCV precision measurements.
It might sound as bad joke, but after reading your fresh experiences, our new metrology grade DMM it should become the ones at 7 ½ digits for DCV ?
8
Stäubli SLK425 & MULTILAM Gold plated banana plugs – Mini Review 

Intro
In the past seven years of operation of ITTSB Blog, I did gain significant experiences and knowledge regarding science of electrical calibration.
While electrical calibrators and high precision multimeter both are designed under strict specifications’,  a true reliable electrical measurement this is possible when human error this is minimal and when test leads in use these are of acceptable quality.

In the past five years at ITTSB testing lab I was using only a specific middle-priced product design of banana plugs, this is banana body with single spring load bar this be in parallel to solid 4mm copper axle.
Regarding test cables I was using double insulated 1.5mm2 (Red & Black), possibly made in Taiwan product, this distributed in Greece with out branding.
By using such three pairs of cables 100 cm long it’s one, I was able for several years to perform my electrical tests and to obtain respectable test results.

End of 2018, I did spent respectable amount of money, so to upgrade my test leads from high-end (medium priced) to high-end of (high priced) category. 

Stäubli brand is the one in Europe this including banana plug product codes in their products portfolio, them qualifying enough for use at electrical calibration test leads.

Regarding electrical wire construction, Stäubli brand again is the one also producing fine stranded wire.
Here the word fine, this translates to single copper core at diameter of human hair.
An high number of such (fine copper strings) they are forming a single fine stranded wire at 2,5 mm2 (which is highest available diameter).

Most powerful Stäubli brand patch-cord these including SLK425 type plug and fine stranded wire at 2,5 mm2 and it is specified for up to 32A.

ITTSB Blog December 2018 
End of November 2018 I was involved buying a used lot of Multi-contact products from the USA at sweet price.
Originally I was aiming for a quantity of XDK1033 alligator clips.
Among them was old stock of SIL425 gold plated banana plugs (20cm patch cord), product quality seems much higher than of what I had touch so far.
Unfortunately for me, these cables were not at equal colored pairs.
So I made the decision to spend approximately 83 Euro so to buy what ever it is required (Stäubli products) so create my own finest collection of finest patch cords and banana wire leads .

Nowadays end of December 2018 I have managed to own a complete selection of best-in-class of wires for calibration testing for medium up to highest counts multimeter.

My collection includes:
Four pairs of SIL425 gold plated banana plugs (20cm patch cord), these will serve creating a chain of four multimeter and voltage linearity inspection by comparison.

Two pairs of L41 banana MULTILAM these be at length of 50 centimeters its wire, these will be used for direct connection at portable calibrator (such best-in-conductivity and stable in connection banana plugs they will eliminate bad contact issues at critical measurements’ as for example micro and Milliamperes).
Wire alone this is dual insulated PVC Stäubli 2,5mm2, this be incredibly useful also for very high resistance measurements’ in which wire isolation material this has increased importance. 

Additional one pair of L41 banana MULTILAM these be at length of 100 centimeters its wire.
This will be useful when voltage or current source equipment's they have bench top format and they are at different height from device under test.
Shunt resistance testing by using DC power supply at the range of 10A is another good reason for having such cables.

And finally one pair of Series SLK425-E these are at length of 100 centimeters its wire.
This product has fully isolated housing at banana plugs, and as such it is recommended for higher voltages up to 600V RMS and at 32A.
 
My own tweaking for decreasing cost of ownership was buying SLK425-E ready made wires at 2M length, and to use portion of their wire length for making my very own cables collection according my preferences.

Stäubli 2,5mm2 wires evaluation:
Regarding banana plugs in use all three Stäubli products as for example the older design of SIL425 gold plated banana plug, and newer design of SLK425-E gold plated banana plug, among with L41 MULTILAM gold plated banana plug, they are all identical in contact resistance and electrical specifications’, they all belong at top-of-the-range (highest quality) of Stäubli products.

Therefore statistics worth noted can be taken by the evaluation of its wire resistance at specific length.
Available lengths are at 20 & 50 & 100 centimeters.
In those tests again HIOKI RM3542A dedicated resistance meter (7 ½ digit) gave detailed and measurements’ which you can trust at the range of few milliohm.

In detail:
20cm wire this measure 2.2960 milliohm (end to end of banana plug).
50cm wire this measure 3.9970 milliohm (end to end of banana plug).
100cm wire this measure 7.0240 milliohm (end to end of banana plug).

Just for comparison I will mention that my older banana plugs (non gold plated) among with 1.5mm2 wire, at about 90cm length they measure a little higher than 12 milliohm (end to end of banana plug).
 
 
Final thoughts and conclusion
I was have to read too many scattered documents so to discover that people working at electrical metrology sector they do now accepts a small portion of ppm changes these caused due the use of gold plated plugs and or of solder type at soldered cables.
Composition of solder this changed in our decade, dangerous substances which were used before they are now banned from the market and because of that we cannot have any more availability of lowest Low-thermal solder wire.
Therefore in a multimeter of 8 ½ digits with one million counts resolution, we should now ignore from our measurement a roughly sum of 6 ppm of changes, and justify this quantity as acceptable variation caused due latest Low-Thermal capabilities of the materials that we use at 2019 on planet earth.
According my understanding in the future we could possibly witness such a 6 ppm unavoidable Low-thermal deviation this to now listed in the column of measuring uncertainty in a high-end multimeter calibration report.

Now, from a less academic point of view, I will say that I am witness of one market in which most industries trying to cheat in product quality so to boost profitability by them delivering something looking as 100% copper wire.
Especially low-end factories in China, they now trying to mimic appearance of a good quality banana plug, by the use of lot of gold paint which identical paint it is used over Christmas decorations for a Christmas tree.
   
For people like me, who we do not accept to be fooled (cheated) and our non-negotiable requirement this is having few but reliable tools in our ownership, the number of choices are much fewer.

While I am greatest enemy of Stäubli pricing policy, I have to admit that products alone, they are made according highest quality and standards.
For example even the humble L41 banana (MULTILAM), this has product design which is a product of lots of thought and attention to detail (work of a serious product designer).
The round barrel which this accepts the wire so to be soldered, this is impressively designed and it does assist soldering process in a way that 100% successful soldering this would be warranted.   

Stäubli wire silicone or PVC both are what you expect that they would be speaking of pure copper wire.

Regarding wire diameter selection, I will use Spartan method of interpretation because this review it is not sponsored, but paid due my own wallet as is 95% of ITTSB blog content.
Feel free reading electrical metrology requirements for calibration test of several DUT and components, then determine your own needs and requirements and then make a choice and stick to it.

My very own choices about type and quantity and quality of test leads for calibration tests are the ones which a calibration enthusiast should also follow, so measuring uncertainty to be solely a problem of the measuring equipment or of the DUT.
9
Το Ελληνικό Ινστιτούτο Μετρολογίας (ΕΙΜ) είναι ο Εθνικός Φορέας Μετρολογίας της Ελλάδος και Σύμβουλος της Ελληνικής Πολιτείας σε θέματα μετρολογίας και μετρήσεων.

http://learn.eim.gr/?page_id=45

Twitter: https://twitter.com/eimgreece
10
Αρχές διακρίβωσης  ψηφιακών πολυμέτρων (Ευαγγελία Τριανταφύλλου) Μάιος 2011 - Βιβλιοθήκη ΑΠΘ

Κάποιοι έχουν την εντύπωση ότι τα πολύμετρα και ο χώρος των ηλεκτρικών μετρήσεων είναι κάτι απλό, ίσως και να είναι για τα πολύμετρα με ένα μόνο ψηφίο.
Όποιος πραγματικά θέλει να κατανοήσει και να δει το βάθος του πηγαδιού που ονομάζετε διακρίβωση  ψηφιακών πολυμέτρων, πρέπει να διαβάσει τα σχετικά τμήματα της εργασίας της Ευαγγελίας Τριανταφύλλου.

http://ikee.lib.auth.gr/record/290858/files/?ln=el
   
Το παραπάνω υλικό είναι ένας θησαυρός, θαμμένος στην Βιβλιοθήκη του ΙΚΕΕ / Αριστοτέλειο Πανεπιστήμιο Θεσσαλονίκης, και θα παρέμεινε θαμμένος εάν η Βιβλιοθήκη δεν ενεργοποιούσε το πρόγραμμα Ψηφιακή Ελλάδα με  συγχρηματοδότηση του ΕΣΠΑ.   

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