My first 10kOhm reference resistor

[BU508A]

Hello,

this is my first attempt to build a 10kOhm lab reference resistor to check ordinary DMM.

Bill of material:
- Vishay Y145310K0000V9L from Digikey
- Hirschmann binding post red, 4mm, part number: PKI 10 A AU RT
- Hirschmann binding post black, 4mm, part number: PKI 10 A AU SW
- Silver wire, 1mm diameter, pure silver (999/1000)
- Bopla case, part number Euromas II ET 210
- Solder: Felder "EL", diameter 0.75mm,  Sn96Ag04, part number: 20960720

Further improvements are planned, such as:
- shielding
- put in some sensors for temperature and humidity
- put in some silica gel
- put in something like an USB stick, so I can store calibration data etc. on it
- something else, which I'm not thinking of it right now 

And here are some pictures:

[LA7SJA]

How much difference is there between two and four wire measurements of the 10K resistor?

Johan-Fredrik

[BU508A]

How much difference is there between two and four wire measurements of the 10K resistor?

My 7510 is reading:
- in 4W mode: 10000,000241 Ohms
- in 2W mode: 10000,000259 Ohms

I will do a 24h measure for both modes and post the data here, but not before next week.

[Vgkid]

How much difference is there between two and four wire measurements of the 10K resistor?

Johan-Fredrik

if you are talking about inside the enclosure, not much if any. Especially is somewhat thick wire is used. In my quest to find out suitable trim resistors. About 6cm of 24awg copper wire yields 2.0mOhms (going from memory). Of course to measure that low a oc ohms meter needs to be used.
   Outside of the enclosure  it does matter.

[grumpydoc]

Very nice project.

Are the meters calibrated and if so how long ago (and do you know the actual difference between the reading and resistance standard).

The Vishay .005% resistors do look very nice, especially as they are less than £35 from Farnell.

Just looking at the readings above and assuming the Vishay is within its specified tolerance would give the following observations:

Ignoring the temperature then the Vishay should have a true value of between 9,999.5 and 10,000.5 ohms so the range of possible displays on the Keithley if it is spec is 9999.17 to 10000.83 ohms¹ and for the 34401A 9998.69 to 10001.31 ohms² so your readings are consistent with that.

The max error on the 34401A is .91 of an ohm (10,000.41 - 9999.5) or 91ppm (0.0091%) and on the Keithley it is 0.743 ohms or 74.3ppm - so you can't quite confirm your meters are in spec.

Looking at it the other way, if the Keithley is in spec the true value of the resistor is between 9999.912 and 10000.573 ohms so you are within a hair of knowing the resistor is within its specified tolerance (just 7ppm out on one end of the uncertainty).

1] 30ppm of reading + 3ppm of range on 10k range within 30 days of autocal.
2] 80ppm of reading plus 1ppm of range within 90 days of cal

[Cerebus]

Also, I would use a similar metal box inside of a plastic box like the Zlymex resistor for temperature lagging-- with some construction-type closed-cell polyurethane foam [in a spray can from my local hardware store] for insulation between the internal metal box and the external plastic box.

Beware - that kind of PU foam is moisture cure (absorbing atmospheric water vapour to cure) and you might not get the results you'd expect with it squirted between two impermeable boxes with a relatively narrow area for inward water vapour diffusion. I'd suggest either a little experimenting first, or use two part PU foam.

The two part stuff is great fun to use  - mix two 50ml shots of liquid and watch them expand to a whole litre of foam. It also comes in many grades including some quite soft ones similar to furniture foam. If using two part *please* follow all the safety instructions particularly with regard to vapour inhalation, I've see people hospitalized who didn't. That warning goes double for asthmatics and others with respiratory illnesses.

[BU508A]

Hello,

Very nice project.

Thank you.

Are the meters calibrated and if so how long ago (and do you know the actual difference between the reading and resistance standard).

Yes, they are. I've purchased the 34401A last year in Sept. on ebay and
it was calibrated on Oct., 13th at Keysight in Böblingen/Germany.

The Keithley DMM7510 was bought last year in December from Instrumex (http://www.instrumex.de/en/product_list).
It was calibrated in Nov. 2015 directly from Keithley.

The Vishay .005% resistors do look very nice, especially as they are less than £35 from Farnell.

I payed at Digikey around 23.- EUR plus shipping.

The max error on the 34401A is .91 of an ohm (10,000.41 - 9999.5) or 91ppm (0.0091%) and on the Keithley it is 0.743 ohms or 74.3ppm - so you can't quite confirm your meters are in spec.

True. My goal was not at this time to build something to check these meters.
What I want to do with this is checking ordinary DMMs with 3 1/2 and 4 1/2 digits.
I hope, this resistor will do it.

Regards,

Andreas

[TiN]

Nice build, and thanks for BOM details, it's not often to see detailed P/Ns for those who want to follow same path.

I'd also drop bag of moisture absorption silicagel to smoothen humidity shifts (as used resistor in not hermetic and can be affected by moisture).

For environment sensors, little temperature-pressure-humidity sensor board can be placed inside, such as BME280, which can be easily interfaced to Raspberry Pi or Arduinos stuff.

[BU508A]

Hello TiN,

Nice build, and thanks for BOM details, it's not often to see detailed P/Ns for those who want to follow same path.

Thank you. :-)
Regarding the BOM: I thought it was a good idea so others could either easily follow or have better ideas what can be used instead.

I'd also drop bag of moisture absorption silicagel to smoothen humidity shifts (as used resistor in not hermetic and can be affected by moisture).

Yes, this is in the queue for my addons/improvements.

For environment sensors, little temperature-pressure-humidity sensor board can be placed inside, such as BME280, which can be easily interfaced to Raspberry Pi or Arduinos stuff.

I'd purchased this device a while ago and I think they are quite nice: Sensirion SHT21, see attached datasheet. There are some shields for arduino, I plan to use the Nano.

Andreas

[BU508A]

Hello Diligent Minds,

[lot of interesting stuff]

Since I am a newbie in all this metrology stuff and you are always writing a lot of interesting things, I have to think about it. 
And the hint with this resistor project from zlymex was very valuable and interesting.

Man, I can see the headaches waveing around the corner .... 

Thank you for your input, really appreciate it.

Andreas

[acbern]

For 3.5 and 4.5 digits this will perfectly do. I did the same some years ago, vishay resistors from digikey, copper telurium bindig posts, but had the intention to use it for calibration of higher grade meters. Useless though, annual drift too high, some in the 10+ppm range pa. So now they are just sitting arround unused on the shelf.I did not add any dissicant as the cases had no gasket, but it would be interesting to know what drift you have in a year using it. That would require low ppm measurements. I could measure your resistor now and in a year if you want, would be interesting for me and maybe also the group to see the impact of dissicant.
Btw, your readings for 4 and 2 wire seem a little optimistic with 10.5 digits.

[BU508A]

Hallo acbern,

I could measure your resistor now and in a year if you want, would be interesting for me and maybe also the group to see the impact of dissicant.

This would be great! I'll bring it with me to the HAM Radio in FN. 

Btw, your readings for 4 and 2 wire seem a little optimistic with 10.5 digits.

Yes, of course. 
But this is what the display showed anyway, will provide a screenshot this evening here. 
Probably this is for confusing purpose ... 

Andreas

[acbern]

Fine, so let me know re. HAM radio.

Ps: I dont own a7150, but how would a 7.5 digit dmm show 10.5 digits?

[grumpydoc]

Fine, so let me know re. HAM radio.

Ps: I dont own a7150, but how would a 7.5 digit dmm show 10.5 digits?

Looking at the pics I'd guess BU508A meant to say that the readings were:

- in 4W mode: 10000,241 Ohms
- in 2W mode: 10000,259 Ohms

Some extra "0"'s seem to have crept in. A difference of 18 milli ohms seems reasonable as it will be due to the test leads.

[TimFox]

"- Silver wire, 1mm diameter, pure silver (999/1000)"  from BOM.

Why silver instead of solid copper?  The difference in resistance is negligible, but there might be thermal EMF differences.
OFHC copper is nice, but I don't think it has any important advantage over "normal" ETP copper, except for its resistance to work hardening/breakage with mechanical flexing.

[BU508A]

Fine, so let me know re. HAM radio.

Ps: I dont own a7150, but how would a 7.5 digit dmm show 10.5 digits?

Looking at the pics I'd guess BU508A meant to say that the readings were:

- in 4W mode: 10000,241 Ohms
- in 2W mode: 10000,259 Ohms

Some extra "0"'s seem to have crept in. A difference of 18 milli ohms seems reasonable as it will be due to the test leads.

Of course, you are right.

Memo to myself: do not post to EEVBlog when to tired. 

Here is an actual screenshot:

[BU508A]

Hello TimFox,

Why silver instead of solid copper?  The difference in resistance is negligible, but there might be thermal EMF differences.
OFHC copper is nice, but I don't think it has any important advantage over "normal" ETP copper, except for its resistance to work hardening/breakage with mechanical flexing.

Well, thermal EMF should be negligible as well, because copper, silver and gold does have the same Seebeck coefficient of 6.5:
https://en.wikipedia.org/wiki/Seebeck_coefficient#Seebeck_coefficients_for_some_common_materials

There were two reasons, but not very good ones:

- Silver has a lower resistance than copper
- Silver is more fancy imho. I do really like silver as a metal, but I can not give a certain reason for this. 

But you are right: pure copper will fit perfectly as well.

Regards,

Andreas

[acbern]

What actually is worse than the silver is the brass in the binding posts. This (against copper) is about 3uV/K, silver is about 0.5. even copper to copper has an emf, since the alloy mixes may be different (but very small, <0.3uV/K).
On the other hand, the effects of this is generally overestimated, since the temperature gradients are so small, and this is not a high precision standard anyway. So for practical purposes, this should be totally ok. And high precision meters can compensate this anyway.

[quarks]

Looks very well done to me

as mentioned by others, possible (moderately priced) improvements are easy:
add a temp sensor
VHP101 (absolute value is not as important as stability, therefore you can go for the cheapest available tolerance, if budget is critical)
use low emf binding posts (like Pomona 3770)

[zlymex]

Very impressive first try!

It seems to me that the spacing between binding posts are more than 0.75 inch(19.05mm).
I don't know exactly why, but all the positive and negative binding posts of commercial standard, multimeters are arranged in this way. Fluke 732A is an exception but changed back on 732B.
Probably because for double banana plugs or adaptors?

[BU508A]

Looks very well done to me

Thank you. 

as mentioned by others, possible (moderately priced) improvements are easy:
add a temp sensor
VHP101 (absolute value is not as important as stability, therefore you can go for the cheapest available tolerance, if budget is critical)
use low emf binding posts (like Pomona 3770)

Adding a temp. sensor is on my list. My goal is: collect some experience in building etc. and do some measures on the device to get a feeling for it. And, of course, hopeing for some valuable input from the folks here. 

VHP101 will be the next step but right now I'm satisfied with the stability < 60 ppm after 10 years load life. See screenshot from datasheet.

Regarding the binding posts: I was looking around to find low EMF Binding posts. There are several available, you have mentioned the ones from Pomona.
Multicontact had some as well but these are discontinued and you can get them only on the surplus market. with some luck. See attached datasheet.
From Mueller electric are Cu-Te binding posts available: http://muellerelectric.com/product-category/banana-plugs-jacks-binding-posts/page/2/
But my favourite are the ones from lowthermal.com: http://www.lowthermal.com/cables-and-connectors.php
They are really nice, but they call around 22 US Dollar per piece. If you are order 10 of one kind. Plus shipping, taxes, custom fees etc.

So, right now to check some 3 1/2 and 4 1/2 DMM I think my first attempt is sufficient. But later on I will go for more stability etc. for my standard lab resistor.
But first getting some experience. 

Andreas

Edit: typos

[BU508A]

Hello zlymex,

Very impressive first try!

Thank you. 

It seems to me that the spacing between binding posts are more than 0.75 inch(19.05mm).
I don't know exactly why, but all the positive and negative binding posts of commercial standard, multimeters are arranged in this way. Fluke 732A is an exception but changed back on 732B.
Probably because for double banana plugs or adaptors?

Yes, you are right, the spacing is not 19,05mm (0,75 inch). I thought, it is not necessary at this time. When I will do the second one, I will do it with a 19,05mm spacing for sure. Just to be compliant.

Andreas

[branadic]

Whats all that Tellurium stuff, Anyhow?

As far as I understood you don't need this tellurium stuff, it's just inside the copper for easier mechanical processing, that's it. But modern turning tools are able to mashine electrolytic copper without any drawback. The galvanic gold plating for keeping things away from oxidation without nickel layer is no secret at all.

[zlymex]

Whats all that Tellurium stuff, Anyhow?

As far as I understood you don't need this tellurium stuff, it's just inside the copper for easier mechanical processing, that's it.  ......

Is the color of  tellurium copper different that pure copper in any way? I got some tellurium copper binding posts but most of them are plated with gold.
Also, do you think the anti-corrosion characteristic is any better than pure copper if not something plated?

[Macbeth]

There does seem to be a mystical audiophool magic type aura with "Tellurium Copper" and Dave doesn't help when fetishising those binding posts in his videos (amusing as it is).

C109 is actually very slightly worse than regular common as muck pure copper C101 electrically. It is much easier to machine though. So the benefit is not to voltnuts, but the manufacturers.