Author Topic: DIY Low EMF cable and connectors  (Read 39341 times)

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Offline cellularmitosis

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Re: DIY Low EMF cable and connectors
« Reply #150 on: August 16, 2017, 03:08:19 PM »
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!).
 

Offline MisterDiodes

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Re: DIY Low EMF cable and connectors
« Reply #151 on: August 17, 2017, 12:49:12 AM »
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.   

« Last Edit: August 17, 2017, 03:16:37 AM by MisterDiodes »
 
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Offline cellularmitosis

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Re: DIY Low EMF cable and connectors
« Reply #152 on: August 17, 2017, 04:17:46 AM »
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!   8)
 

Offline pelule

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Re: DIY Low EMF cable and connectors
« Reply #153 on: August 17, 2017, 05:34:52 AM »
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
You will learn something new every single day
 
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Offline MisterDiodes

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Re: DIY Low EMF cable and connectors
« Reply #154 on: August 17, 2017, 07:04:57 AM »
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. ;D

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.
 

Online Echo88

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Re: DIY Low EMF cable and connectors
« Reply #155 on: August 17, 2017, 07:17:23 AM »
Why dont they supply >= 6.5 digit DMMs with binding posts as a standard? Beauty-reasons?
 

Offline MisterDiodes

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Re: DIY Low EMF cable and connectors
« Reply #156 on: August 17, 2017, 07:25:49 AM »
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.
 
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Offline cellularmitosis

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Re: DIY Low EMF cable and connectors
« Reply #157 on: August 17, 2017, 08:15:03 AM »
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...
 

Offline MisterDiodes

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Re: DIY Low EMF cable and connectors
« Reply #158 on: August 17, 2017, 09:53:59 AM »
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!
 
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Offline quarks

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Re: DIY Low EMF cable and connectors
« Reply #159 on: August 17, 2017, 06:30:01 PM »
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...

about adapters have a look

http://www.eevblog.com/forum/testgear/lking-for-gold-plated-tellurium-copper-banana-plugs/msg246371/#msg246371

http://www.eevblog.com/forum/testgear/lking-for-gold-plated-tellurium-copper-banana-plugs/msg327291/#msg327291
« Last Edit: August 17, 2017, 06:34:56 PM by quarks »
 

Offline cellularmitosis

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Re: DIY Low EMF cable and connectors
« Reply #160 on: September 08, 2017, 09:49:42 AM »
Maybe some of you guys find this trick useful:

I threw some normal crimp spade lugs in citric acid and after 2 weeks the relevant tin layer was etched away, yielding lowest cost pure copper (according to an exemplary manufacturer >99,9% electrolytic copper) spade lugs suitable for nanovolt-stuff.
Of course hydrochloric acid and oxygen peroxide would etch way faster, but i didnt have that stuff lying around.

Echo88, I've replicated your results using citric acid.  I just cut up a few pieces of some cheap crimp connectors as a test.

If I recall, this was 60 grams of water, and 12 grams of citric acid powder (i.e. 20% by weight).

I got lazy about removing them, so they were in there from 8/16 through 9/6, but they were mostly stripped after about 7 to 10 days.  You do need to agitate them to ensure all surfaces are exposed to the acid, daily agitation would be good.

(the large welding cable connector is just for color -- it came as bare copper from the factory and is used as a color reference only).
« Last Edit: September 08, 2017, 10:17:57 AM by cellularmitosis »
 

Offline cellularmitosis

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Re: DIY Low EMF cable and connectors
« Reply #161 on: September 08, 2017, 09:54:59 AM »
Next into the bath: some 1/4 inch spade connectors (Morris #11520) from amazon.com.  These are the right size to accommodate e.g. a pomona 3770.

Unfortunately, the crimp loop was a bit larger diameter (16-22AWG, or 1.25mm) than I'd hoped for (I'm hoping to be able to crimp to a single CAT5 strand directly).  I can probably use a hammer, punch, and anvil to do the job.

See you in a few weeks!

Hrmph, it appears these are already "no longer available" on amazon.

Here's a google shopping search.  They are available for $13 / 100 pack: https://www.google.com/shopping/product/14631136190881433596?rlz=1C5CHFA_enUS708US708&biw=998&bih=1454&q=Morris+11520+spade&oq=Morris+11520+spade&sa=X&ved=0ahUKEwiMn83lppTWAhVkl1QKHTuZCNEQ8wIIvwEwAA
« Last Edit: September 08, 2017, 10:14:01 AM by cellularmitosis »
 

Offline cellularmitosis

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Re: DIY Low EMF cable and connectors
« Reply #162 on: September 08, 2017, 10:06:31 AM »
It turns out these connectors follow a naming convention, e.g. SNB1.25-6, OT2-4, UT1.5-3, etc.

SNB, OT, UT describe the kind of connector (fork vs ring, both SNB and UT appear to be forks, OT appears to be a ring).

The first number describes the diameter of the crimp opening (e.g. 1.25 mm).

The second number describes the fork / ring opening clearance (-6 is 6.2 mm, about 1/4 inch).

You can find these by the thousand pack for under $10 on alibaba and toaboa, but at those prices they are likely to be brass rather than copper.

I find it hilarious that unplated copper connectors sell at a crazy premium compared to tin-plated-copper connectors.  In theory, they should be cheaper (one less manufacturing step).

The size we want (to accommodate a pomona 3770) is the 1/4 inch stud (-6), and for crimping to CAT5 / telephone wire, I think you'd ideally want a 1mm crimp opening, so you're looking at either SNB1-6 or UT1-6.  Domestically, the closest I've been able to find is SNB1.25-6 (this is the size of the Morris #11520 connectors).

I have seen UT1-6 available on taobao, but copper vs. brass is going to be luck of the draw there, and minimum quantity will likely be a bag of 1000.
« Last Edit: September 08, 2017, 10:22:26 AM by cellularmitosis »
 

Offline manganin

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Re: DIY Low EMF cable and connectors
« Reply #163 on: September 08, 2017, 06:28:31 PM »
copper vs. brass is going to be luck of the draw there

But there are also honest sellers:

Quote
Product Name: Non Insulated Fork Terminal
Model: SNB1.25-6S
Material: Metal
Color: Silver Tone

http://www.ebay.com/itm/311026743780

 

Offline SZA263

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Offline cellularmitosis

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Re: DIY Low EMF cable and connectors
« Reply #165 on: September 09, 2017, 10:15:50 AM »
Looks pretty good

https://world.taobao.com/item/546621717699.htm

0.01C, these arrived today, and they in fact are solid copper.
 

Offline cellularmitosis

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Re: DIY Low EMF cable and connectors
« Reply #166 on: September 09, 2017, 10:28:04 AM »
With these (and a few other items), I discovered a little hitch in the taobao game. 

Some sellers will ship the items directly to you.  When this happens, you just pay once, and you know the total cost up-front.

Other sellers ship the item to some sort of exporting warehouse.  So the amount you are paying upfront isn't the total cost -- a few days later you get hit with additional shipping charges, and they seem to be fairly expensive.  Unfortunately, I haven't been able to figure out a way to detect which situation will happen ahead of time.

In this case, the binding posts which look like a copper pomona 3770 clone were shipped directly to me, and the cost was known up-front.  But with these latest bare-copper binding posts (which don't have banana jacks), I got hit with an additional $13 shipping charge, which made the other posts a bit of a better deal.

The copper pomona 3770 clones ended up $36.77 for 8 posts (about $3.83 each plus $6.13 shipping), making them effectively $4.60 eachhttps://world.taobao.com/item/40823926055.htm

These most recent bare-copper posts were $33.11 for 10 posts (about $2.85 each plus $4.63 shipping), but with an additional $13.13 warehouse shipping charge, making them effectively $4.62 eachhttps://world.taobao.com/item/546621717699.htm

I don't want to paint a rosy picture of taobao -- so far I've paid for two items which haven't arrived in over a month (a few cheap banana plugs, but also a pair of LT1088 chips which were $18 each, ouch!) -- likely I just got scammed.
« Last Edit: September 09, 2017, 10:31:34 AM by cellularmitosis »
 

Offline 0.01C

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Re: DIY Low EMF cable and connectors
« Reply #167 on: September 09, 2017, 11:39:38 AM »
With these (and a few other items), I discovered a little hitch in the taobao game. 

Some sellers will ship the items directly to you.  When this happens, you just pay once, and you know the total cost up-front.

Other sellers ship the item to some sort of exporting warehouse.  So the amount you are paying upfront isn't the total cost -- a few days later you get hit with additional shipping charges, and they seem to be fairly expensive.  Unfortunately, I haven't been able to figure out a way to detect which situation will happen ahead of time.

In this case, the binding posts which look like a copper pomona 3770 clone were shipped directly to me, and the cost was known up-front.  But with these latest bare-copper binding posts (which don't have banana jacks), I got hit with an additional $13 shipping charge, which made the other posts a bit of a better deal.

The copper pomona 3770 clones ended up $36.77 for 8 posts (about $3.83 each plus $6.13 shipping), making them effectively $4.60 eachhttps://world.taobao.com/item/40823926055.htm

These most recent bare-copper posts were $33.11 for 10 posts (about $2.85 each plus $4.63 shipping), but with an additional $13.13 warehouse shipping charge, making them effectively $4.62 eachhttps://world.taobao.com/item/546621717699.htm

I don't want to paint a rosy picture of taobao -- so far I've paid for two items which haven't arrived in over a month (a few cheap banana plugs, but also a pair of LT1088 chips which were $18 each, ouch!) -- likely I just got scammed.
for your reference

http://www.howtotao.com/buy-from-taobao/

https://world.taobao.com/item/45907925781.htm

http://www.taobaoguides.com/2016/07/06/the-best-way-to-ship-taobao-packages-from-china-to-usa-and-eu-countries
Guildline Datron Fluke L&N ESI HP
0.01C
 
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Offline cellularmitosis

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Re: DIY Low EMF cable and connectors
« Reply #168 on: September 10, 2017, 05:53:03 AM »
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. ;D

So it turns out MisterDiodes can predict the future...

Edit: derp, wrong picture
 
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Offline branadic

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Re: DIY Low EMF cable and connectors
« Reply #169 on: September 14, 2017, 05:52:24 AM »
A question to those that are familiar with the topic. Is it really necessary that the outer insulation is PTFE too? I found cable for RTDs, with PTFE insulation on the single wires, 4 wires twisted and shielded, but with PFA for the outer insulation. So the question is, does it really make any difference if the outer insulation is non PTFE?

-branadic-
Prema 5000 | Prema 5017 SC | Keithley 181 | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, HDO6054, Keysight 53230A and other goodies at work
 

Offline The Soulman

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Re: DIY Low EMF cable and connectors
« Reply #170 on: September 14, 2017, 06:15:59 AM »
A question to those that are familiar with the topic. Is it really necessary that the outer insulation is PTFE too? I found cable for RTDs, with PTFE insulation on the single wires, 4 wires twisted and shielded, but with PFA for the outer insulation. So the question is, does it really make any difference if the outer insulation is non PTFE?

-branadic-

You do the math,it's on the outside of a braided shield.  :)

Here is something that could belong here, a quote from myself from the ltz1000 thread but didn't get a reply there so re-post it here:

Zener voltage reading by SMA connectors? SMA is not good for low thermals, as connector package is usually gold plated brass. You want only copper/copper connections with minimal amount of junctions (best is single twisted wire direct from zener to DMM binding posts) to get accurate microvolt-level measurements.

Ok not the best, but realistically what thermal-gradient do you expect there to be on that connector?
And how does the base metal of the connector matter as all connections are made on the same gold surface? When mating the two (assume crimped )connectors it would be copper-gold-gold-copper?

My gut tells me to be more concerned in areas where larger thermal-gradients do exist such as the connection to the kovar legs of the heated reference and to the oxidized binding posts of some warm ancient dmm.  :box:

Not that I'm a expert, just asking to learn something.  :-+

This low thermal connections are very important for accurate readings, but is starting to smell like some audio related behavior.  :-//
No point in making a point just to make a point, that would be pointless.
 

Offline Edwin G. Pettis

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Re: DIY Low EMF cable and connectors
« Reply #171 on: September 14, 2017, 08:59:54 AM »
"This low thermal connections are very important for accurate readings, but is starting to smell like some audio related behavior."


The answer is that thermal EMFs, usually in microvolts, becomes important when attempting to accurately measure PPM, at lower accuracy, say ~25PPM or higher, the thermals becomes less important as they are a proportionately smaller than the measurement's signal value in general.  In practice it is a good idea to minimize thermal EMFs at all times as they represent an uncertainty factor in the measurement which can vary.  For example, a resistor with ±.0025% tolerance, a couple microvolts of thermals aren't very important, at ±.001%, now they've become significant as they could represent 2PPM, 3 PPM or more of error,  a null meter is the best instrument for detecting this.

PPM measuremenvts are almost always at microvolt or lower potentials so thermal EMFs become very important, they are not part of the audiophoole mythology. 
 

Offline MisterDiodes

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Re: DIY Low EMF cable and connectors
« Reply #172 on: September 15, 2017, 10:00:29 AM »
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. ;D

So it turns out MisterDiodes can predict the future...

Edit: derp, wrong picture

You thought I was kidding... :-DD  I hope your '845 works well, these nullmeters will open up a new low-ppm world of discovery for you.  Be patient with it at the low end though...What you think is the needle floating around at 1uV and 3uV range is probably a thermal somewhere in your setup....There will be plenty of that.
 
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Offline BU508A

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Re: DIY Low EMF cable and connectors
« Reply #173 on: September 15, 2017, 04:20:55 PM »
Hi branadic,

[...]
does it really make any difference if the outer insulation is non PTFE?

In my opinion: no. There are two or three main reasons, why using PTFE:
- high insulation resistance
- heat resistance
- low dissipation factor

https://www.druflon.com/ptfeprop.html

For the outer insulation, PFA is very fine.

Good example: inner insulation: PTFE, outer insulaton: FEP (cable is RG 400 U)
http://www.ebay.com/itm/162634086255

Andreas

“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 

Offline BU508A

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Re: DIY Low EMF cable and connectors
« Reply #174 on: September 15, 2017, 04:42:57 PM »
I just stumbled over this page:
https://goo.gl/kfkKWN (link goes to google books and sorry the site is in german. But the table shown is interesting, chapter 0.2.3.9).

Does this table suggest, that a smart combination of copper, silver and gold will give you some kind of compensation effects?
All metals were paired to copper.

from the table:
thermal emf copper - gold:  +0,1µV
thermal emf copper - silver: -0,2µV

Thanks,

Andreas
“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 


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