DIY Low EMF cable and connectors

[cellularmitosis]

I have a question about the payment scheme - I suppose that Alipay is linked with buyers Visa or bank account - can you comment ?

Is there something as AliPay protection if goods do not show up - like there is with Aliexpress ?

Yeah, mine is linked to a Visa card.

Not sure about what sort of protection they have.  I'm actually discovering what ebay's process is right now -- I won an HP 3457A for $150, only to have it apparently delivered to the wrong address by fedex...

[onemilimeter]

Hi...

I found this Teflon (PTFE) cable (shielded, silver plated, 19x0.2mm) from Taobao...
https://world.taobao.com/item/525683103258.htm

The seller wrote it's imported from Japan, manufactured by Junkosha Inc (http://www.junkosha.co.jp/english/)

The outer insulator (brown color layers) is Teflon/PTFE... but I'm not sure about the inner insulator (white color and black color layers)... if I buy it how can I test to tell if it's Teflon/PTFE?

Thanks

[cellularmitosis]

I think you could use an electrometer to compare leakage against the same length of some CAT5.  What is the most sensitive current range you have available on your instruments?

[Andreas]

why not make a simple test with a soldering iron.
Teflon should withstand around 200 deg C.

With best regards

Andreas

[cellularmitosis]

bigclive has an interesting way of testing finely stranded wire to see if it is actually copper, or just copper coated aluminum (which apparently is a common cost-saving trick in the ebay junk he loves to review).  If you hold the flame of a lighter against the strands, copper coated aluminum will crinkle up like a dead spider, but pure copper is basically unaffected.

[onemilimeter]

I think you could use an electrometer to compare leakage against the same length of some CAT5.  What is the most sensitive current range you have available on your instruments?

I may have access to a Keithley 2002. Can this instruments do the job? Thanks.

[SeanB]

Strip an end and use a lighter. If it burns it is PVC or some other plastic, and if it just chard and makes a noxious smoke it is PTFE.

Likely though if the outer sleeve is PTFE the inner is as well, as that type of cable is common in avionics as a data wire or shielded cable for low level signals.

[cellularmitosis]

I found two plugs which appear to be the same style (one solid chunk of copper with a threaded end):

https://world.taobao.com/item/529066733817.htm

https://world.taobao.com/item/550387066144.htm

I've ordered a few of each.  When they arrive, I'll cut into one of them (or try the citric acid trick) to see if they are really copper inside.

Welp, the first set arrived.  It looks like they are gold-plated brass, although they almost feel too light to be brass.  (I filed off the outer plating, and the surface and shavings have the appearance of brass).

I wonder if there is an easy chemical test to check for brass?  I know that copper will turn some acids bright blue...

[cellularmitosis]

So after watching this Transmille video where he demonstrates using a null voltmeter to directly measure a thermal EMF, I decided to take the plunge and bought an HP 419A on ebay.

https://youtu.be/KiYhEP6m7Pc?t=1m23s

In a few weeks I hope to be able to measure thermal EMFs directly!

[0.01C]

So after watching this Transmille video where he demonstrates using a null voltmeter to directly measure a thermal EMF, I decided to take the plunge and bought an HP 419A on ebay.

https://youtu.be/KiYhEP6m7Pc?t=1m23s

In a few weeks I hope to be able to measure thermal EMFs directly!

buy keithley 155 or Fluke 845 is better

[ManateeMafia]

My money says it's brass. I am more interested in finding out what they used for the external plating.

A null meter is invaluable and at least the seller gives a 14 day warranty. You may want to see what kind of chopper amp was used but I have recently taken photos of an ESI 801 and it used the HP 419 as the null meter. very nice looking inside.

[cellularmitosis]

buy keithley 155 or Fluke 845 is better

Yeah, I did a bit of homework.  Those are nicer units, but they are out of my "splurge" price range (they are $200+ on ebay at the moment).

There are a lot of Leeds & Northrup models for ~$50, but their lowest range is 1mV.

The 419A's lowest range is 3uV, and the price was right, so that's the one I settled on.

(I think a fun project might be to see if you can get a Leeds & Northrup unit for $25 using "best offer", then gut it and install Conrad Hoffman's null detector circuit from his mini-metrology-lab article series)

[cellularmitosis]

I wonder if there is an easy chemical test to check for brass?  I know that copper will turn some acids bright blue...

Hmm...

Apply a small amount of hydrochloric acid to an area of the brass. Test only a small area because the test is corrosive. Unlike some metals, brass turns pink when it is tested with hydrochloric acid.

via http://ourpastimes.com/identify-brass-metal-8529918.html

[cellularmitosis]

I bought some copper spade lugs from China ,not bad.

Great find!  I've been searching for unplated copper spades, but haven't had any luck.  Can you reveal a link to where you found these?

[cellularmitosis]

Very interesting Echo88!  I think I'll try that myself.

Would something like this work?  Powdered food-grade citric acid?  https://www.amazon.com/gp/aw/d/B00EYFKKZC/ref=sxts_sxwds-tsp_1_a_it?ie=UTF8&qid=1501683294&sr=1

TiN, 0.01C, can you guys post a link to the taobao seller who sells those binding posts?  I'd like to order some.

My first victim to go into the citric acid bath was a cheap "logico" banana plug, which appear to be a clone of Nakamichi banana plugs.

A few days into the acid, the body of the connector started to take on a reddish hue, and I thought they might actually be copper.

However, after about another week, and after taking them out of the acid for a while, they were a much darker, brownish color.  Filing away the body reveals what looks like brass.

[cellularmitosis]

I took interest in the "logico" plugs because I was trying to get away from plugs which had a loose-fitting free-spinning contact barrel-spring.  The logico plugs were of a style where the contact spring was attached solidly to the body, which I thought would be better for precision measurements.

Then, while searching for unplated copper banana plugs, I came across the plugs marketed at audiophiles:

http://www.douglasconnection.com/Furez-TSTSB60NP-Bare-Copper-Banana-Plug-Connectors-Pair-FZTSTSB60NP.htm

I liked the design of these plugs even better, as they were a single, solid piece of material, and it seemed there would be even more surface area in contact with the DMM's socket.  They also claimed to be tellurium copper, so even though they are priced for audiofools, I decided to order a pair for use as a low thermal EMF "benchmark".

Then, just this evening, I stumbled upon the fact that this style of connector has a name.  If you search for "BFA banana", you'll find plugs like this.

https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Delectronics&field-keywords=bfa+banana

https://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=bfa+banana&_sop=7

https://www.aliexpress.com/wholesale?&SearchText=bfa+banana

Taking it a step further, you'll find plugs marketed as "low mass", which appear engineered to have a little mass as possible.  This also seems desirable for minimizing thermal EMF's.

I managed to find an ebay seller who sells unplated copper "low mass" BFA-style banana plugs, and I've just ordered a few.  They are just under $3 each, so not cheap but also not audiofool-priced.  I'll keep you posted!

http://www.ebay.com/itm/162631332431

[cellularmitosis]

Here's a better shot, comparing the color of tellurium copper, the dark de-plated connector, a filed off section, and a "gold" plated original connector.

(the red pliers, blue matt, and white paper are to help with white balance.  capturing metal in a photo without turning it into a mess of glare is hard!).

[MisterDiodes]

Just a head's up since this is metrology section: "Precision" connector as in chasing low ppm measures (if that's what you're doing) means no banana plugs; just use a -clean- direct wire connection to binding post whenever possible.  The best low emf connections for low-ppm precision are clean copper to clean copper - or for easier cleaning the use of gold plated copper (typically will be gold flash over nickle over copper) connections are good also.

Using a -clean- piece of solid copper wire slipped into the cross hole of a binding post really is relatively good "precision" connection and is considered better than any slip-in banana plug style.  "Shrouded" banana plugs and sockets are not going to help low ppm measures.

You'll see this inside a lot of null meters, and learn the manufacturing nuance:  The inside connection to the binding copper post is usually a spade connector under a couple nuts on the threaded shaft (not soldered), usually gold plated and crimped spades.  If you make the -same-  type of connection with the same material on the external part of the binding post, you've basically cancelled most thermal EMF effect right there at one binding post (both end connections at the same post of same material combination at same temp cancel out thermal emf).  Any other unbalanced thermal effect is greatly reduced by keeping the binding posts at the same temp.

The general problem with something like a raw solid copper male banana plug is A) They always need to be cleaned of oxide before use and B) they are fairly soft, wear easily and tend to lose their spring-contact force - and that means it's harder to get a repeatable connection the more the connector is used.  So that means you'll keep these for your more "special" setups, not for everyday general use.

That's why for a general use: a good spring-rate brass alloy (with overplate nickel / tin / gold) is typically used for any connector requiring a spring force on the metal to metal contact area - that means longer contact life / more mating cycles.

If you're using a plain copper banana plug, ideally that would slip into a plain copper socket - but that socket would be a bit harder to keep clean.  The worst connection you could make for a "precision" setup is copper on oxide!

The worst banana plugs for high precision repeatable measures would be the type with the loose spinning plug end - the solid style like you found is better.

Those setscrews on the side of the banana plug are a place for problems to start especially if you're using stranded wire.  Keep an eye on that.  Wire strands have a really bad habit of wiggling out from under setscrews, and if these leads would see a lot of use we'd use a copper ferrule crimped onto the stranded wire wherever it's going to be under simple screw clamps like that.   

[cellularmitosis]

Thanks MisterDiodes, that's great advice.

My hunt for the perfect banana plug is in an attempt to solve the budget metrologist's problem of "my best meter has banana sockets, not binding posts".  That budget metrologist will never be able to achieve a "perfect" setup, but given that, the question is "how close can they get?".

For example, the 34401A (if you can find one under $250) represents a very good bargain for the budding volt-nut, but sadly, only comes with banana sockets.  In spite of that, the budding volt-nut is someone I want to support in their quest, and hopefully I'll come up with some useful findings!   

[pelule]

Just a may be stupid question about thermal EMF at the 6.5 digit voltmeters 34401A:
  Lowest DC voltage range is 100.0000 mV @ 0.1µV resolution
  But best accuracy is +/-3µV +/- 0.5uV/°C plus the reading error.
      ref data sheet, 24 hour accuracy: 30ppm (reading) + 30ppm (range) + 5ppm/°C (reading) + 5ppm/°C (range)
So in my understanding the thermal EMF is not the biggest issue here.
/PeLuLe

[MisterDiodes]

Good point about 34401.  But remember Cellular has his null meter coming, which will lead to a much better Keithley 155 / Fluke 845a / or ?? + 7-decade KVD plus some 732's also. He's got the infection, which means he'll be very broke (but very accurate on DCV measures) in no time.

Even a good working 3456a will get you nice & stable, low noise 6.5 digits measure if you have the space for one - and they are cheap & easy to keep in cal.   Nice units.

There's a reason meters with recessed banana plugs don't make it into the cal room.  For one of our clients The Tek / Keithley sales guy got so frustrated and desperate a few years ago  they caved in and supplied some custom-modified meters with good binding posts... so it does happen if a larger order is possible.

[Echo88]

Why dont they supply >= 6.5 digit DMMs with binding posts as a standard? Beauty-reasons?

[MisterDiodes]

Mostly companies working with Gov'ts trying to regulate in safety arc-flash specs and various CAT-level instrument ratings...  Which is certainly OK if you're working in that environment, but not so good for low ppm work.

[cellularmitosis]

Hmm, perhaps I am barking up the wrong tree?  I.e. Perhaps I should instead be investigating how best to hack some Pomona 3770's into it?  Couldn't hurt -- even if I botch it, i still have a rear set of inputs!

Although, chasing after low EMF bananas is still useful from an inclusion perspective -- for ensuring that the widest audience of budding volt nuts can participate (I can't expect everyone to hack their meter).

Mr Diodes, you have me nervously laughing.  I have made a few additional purchases recently which I haven't even revealed on the forum yet.  Cash poor but D.C. accurate does seem to be the prognosis...

[MisterDiodes]

The other trick is to make or buy an adapter board that brings out those child-safe recessed banana sockets to dangerous binding posts... Male plugs on one side, binding post on the other.  There are photos on EEVblog...

It is not unheard of in the lab is just bypass those stupid shrouded sockets altogether and solder wire direct to the input section of the meter - then you just snip a little wire off the free end for new experiments, and replace the wire now and then.  Not exactly elegant I know  - but do what you have to do...

None of this is a huge issue for 34401 but you'll get there with more sensitive experiments and other setups, especially with a null meter.  Once you play with a 3uV scale null meter, then you can get some time on a 1uV or smaller scale meter, and you can move the needle with your eyes only... Not really but that's what it seems like sometimes.  You can see the effect of just the heat of your hand on one side of the connection.

For now you'll have fun and learn a lot in the world of null meters... You can play with the null meter and find out how connections work (or not).  You'll probably find out that if you use the same type of connection on both ends of a binding post you'll get pretty good results.

Don't forget when you do a null measure between two voltage sources with that meter, get everything zeroe'd out...and then reverse the connections.  Make a change on a voltage source of that difference divided by 2.  Keep doing that until the needle is pretty steady even when you flip your connections around and then that's your compensated null point that is relatively free of thermal emf.  You'll need a stable voltage source and a KVD now also <Grin>.  You don't need that retirement fund do you?

If you're measuring just a connector with that meter you can get your experiment setup and meter zeroed out, then heat one side of the connector only.  Then flip the connections around and try again, and that will show you what's really happening at the connector itself.  Fun stuff!