My first 10kOhm reference resistor - Page 1
Forum section: electronics / general

author: BU508A
author_rank: Super Contributor
timestamp: June 09, 2016, 08:52:49 pm
content: 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: 20960720Further 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 nowAnd here are some pictures:

author: LA7SJA
author_rank: Regular Contributor
timestamp: June 09, 2016, 09:13:41 pm
content: How much difference is there between two and four wire measurements of the 10K resistor?Johan-Fredrik

author: BU508A
author_rank: Super Contributor
timestamp: June 09, 2016, 09:21:24 pm
content: Quote from: LA7SJA on June 09, 2016, 09:13:41 pmMy 7510 is reading:- in 4W mode: 10000,000241 Ohms- in 2W mode: 10000,000259 OhmsI will do a 24h measure for both modes and post the data here, but not before next week.

author: Vgkid
author_rank: Super Contributor
timestamp: June 09, 2016, 09:26:17 pm
content: Quote from: LA7SJA on June 09, 2016, 09:13:41 pmif 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.

author: grumpydoc
author_rank: Super Contributor
timestamp: June 09, 2016, 10:06:19 pm
content: 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 ohms1and for the 34401A 9998.69 to 10001.31 ohms2so 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'tquiteconfirm 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

author: Cerebus
author_rank: Super Contributor
timestamp: June 10, 2016, 12:36:20 am
content: Quote from: DiligentMinds.com on June 09, 2016, 10:53:40 pmBeware - 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.

author: BU508A
author_rank: Super Contributor
timestamp: June 10, 2016, 05:17:05 am
content: Hello,Quote from: grumpydoc on June 09, 2016, 10:06:19 pmThank you.Quote from: grumpydoc on June 09, 2016, 10:06:19 pmYes, they are. I've purchased the 34401A last year in Sept. on ebay andit 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.Quote from: grumpydoc on June 09, 2016, 10:06:19 pmI payed at Digikey around 23.- EUR plus shipping.Quote from: grumpydoc on June 09, 2016, 10:06:19 pmTrue. 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

author: TiN
author_rank: Super Contributor
timestamp: June 10, 2016, 05:34:34 am
content: 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 beeasily interfacedto Raspberry Pi or Arduinos stuff.

author: BU508A
author_rank: Super Contributor
timestamp: June 10, 2016, 06:01:28 am
content: Hello TiN,Quote from: TiN on June 10, 2016, 05:34:34 amThank 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.Quote from: TiN on June 10, 2016, 05:34:34 amYes, this is in the queue for my addons/improvements.Quote from: TiN on June 10, 2016, 05:34:34 amI'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

author: BU508A
author_rank: Super Contributor
timestamp: June 10, 2016, 06:14:30 am
content: Hello Diligent Minds,Quote from: DiligentMinds.com on June 09, 2016, 10:53:40 pmSince 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

author: acbern
author_rank: Frequent Contributor
timestamp: June 10, 2016, 08:03:40 am
content: 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.

author: BU508A
author_rank: Super Contributor
timestamp: June 10, 2016, 08:23:22 am
content: Hallo acbern,Quote from: acbern on June 10, 2016, 08:03:40 amThis would be great! I'll bring it with me to the HAM Radio in FN.Quote from: acbern on June 10, 2016, 08:03:40 amYes, of course.But this is what the display showed anyway, will provide a screenshot this evening here.Probably this is for confusing purpose ...Andreas

author: acbern
author_rank: Frequent Contributor
timestamp: June 10, 2016, 01:05:35 pm
content: 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?

author: grumpydoc
author_rank: Super Contributor
timestamp: June 10, 2016, 02:05:35 pm
content: Quote from: acbern on June 10, 2016, 01:05:35 pmLooking at the pics I'd guess BU508Ameantto say that the readings were:- in 4W mode: 10000,241 Ohms- in 2W mode: 10000,259 OhmsSome 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.

author: TimFox
author_rank: Super Contributor
timestamp: June 10, 2016, 04:12:42 pm
content: "- 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.

author: BU508A
author_rank: Super Contributor
timestamp: June 10, 2016, 06:01:09 pm
content: Quote from: grumpydoc on June 10, 2016, 02:05:35 pmOf course, you are right.Memo to myself: do not post to EEVBlog when to tired.Here is an actual screenshot:

author: BU508A
author_rank: Super Contributor
timestamp: June 10, 2016, 06:09:28 pm
content: Hello TimFox,Quote from: TimFox on June 10, 2016, 04:12:42 pmWell, 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_materialsThere 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

author: acbern
author_rank: Frequent Contributor
timestamp: June 11, 2016, 05:52:42 am
content: 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.

author: quarks
author_rank: Frequent Contributor
timestamp: June 11, 2016, 12:54:18 pm
content: Looks very well done to meas mentioned by others, possible (moderately priced) improvements are easy:add a temp sensorVHP101 (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)

author: zlymex
author_rank: Frequent Contributor
timestamp: June 11, 2016, 02:41:45 pm
content: 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?

author: BU508A
author_rank: Super Contributor
timestamp: June 11, 2016, 06:41:01 pm
content: Quote from: quarks on June 11, 2016, 12:54:18 pmThank you.Quote from: quarks on June 11, 2016, 12:54:18 pmAdding 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.phpThey 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.AndreasEdit: typos

author: BU508A
author_rank: Super Contributor
timestamp: June 11, 2016, 06:48:42 pm
content: Hello zlymex,Quote from: zlymex on June 11, 2016, 02:41:45 pmThank you.Quote from: zlymex on June 11, 2016, 02:41:45 pmYes, 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

author: branadic
author_rank: Super Contributor
timestamp: June 11, 2016, 07:18:45 pm
content: 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.

author: zlymex
author_rank: Frequent Contributor
timestamp: June 12, 2016, 12:11:23 am
content: Quote from: branadic on June 11, 2016, 07:18:45 pmIs 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?

author: Macbeth
author_rank: Super Contributor
timestamp: June 12, 2016, 01:43:46 am
content: 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.

author: ap
author_rank: Frequent Contributor
timestamp: June 12, 2016, 09:06:22 am
content: The audiophooles have the same problem that they need to manufacture a copper post/plug, so they need copper tellurium too, but some abused it by making it mysterious. It is not, normal copper simply smears when milled. They could use brass just as well, but thats a different storry. Here, if you need low emf, Cu-Te is mandatory.

author: quarks
author_rank: Frequent Contributor
timestamp: June 12, 2016, 12:32:33 pm
content: as discussed many times, Tellurium is not what makes a connector low emf.CuTe is only used because of the bad machinabiltiy of pure copper.

author: ap
author_rank: Frequent Contributor
timestamp: June 12, 2016, 02:16:57 pm
content: Yes, it actually makes EMF a little worse, just as beryllium in copper does when spring type plugs are needed, or the gold plating on CuTe posts, but its neglectable. Gets important in the nV range (see data proof spades or EM electronics contacts).

author: BU508A
author_rank: Super Contributor
timestamp: June 12, 2016, 07:28:22 pm
content: So, it makes no difference at all to use Cu-Te or Cu-Be? It is "only" improving the machinability of Cu (as I read in some articles)?This brings me to another question: If I have a binding post, core of pure copper or some Cu-alloy and it is plated with a thick Gold coating all around, would this not compensate the Seebeck effect, assumed, that we have nearly the same temp. everywhere?---- current flow ----->|~|***********|~|---------------|~|***********|~|------------------|~|***********|~|---------------|~|***********|~|------------------|~|***********|~|^ ^ ^Cu-wire | Cu-alloy core | Cu-wire| |Gold coating----------'And would this not mean, that I can still use these Hirschmann Gold plated binding posts? I do really like them.

author: ap
author_rank: Frequent Contributor
timestamp: June 12, 2016, 07:58:42 pm
content: The temperature gradient across the gold layer is so small that no emf voltge issues are expectable (at this level). So with the hirschmanns, you essentially have copper to brass, and that you can measure

author: BU508A
author_rank: Super Contributor
timestamp: June 25, 2016, 08:58:16 pm
content: Here is a little update to my reference resistor prototype.I've putted an Arduino nano controller into it together with a sensor for temperature and humidity, which comes as an Arduino shield. The sensor itself is a SHT 21 from Sensirion (a Swiss company). The datasheet can be found above for download. The little red pcb is a level shifter between 3.3V and 5V for the I²C bus. It is bidirectional.The prototype PCBs I'm usually using are from this company:http://www.roth-elektronik.com/en- one can get them at Reichelt for example (https://secure.reichelt.de/)I will attach the program listing of the nano here as well. Please be kind, I'm not a very good programmer.<placeholder for the bom, will follow>And here are some pictures (and no, the wires aren't pure silver :-) )

author: BU508A
author_rank: Super Contributor
timestamp: June 25, 2016, 09:02:42 pm
content: Here are some more pictures. This is the adapter case to do the connection between USB and the case (cases, there will be more) of the controller inside the resistor case. The case for the adapter was first used for another little project but I drilled one hole at the wrong place so I was reusing it here.