I cheat.
Solder a string of low resistance (or not so low) together.
Applied a current limited current to the string.
The lab supply could be set to ~0.1A and apply 4.4V to the string of 20 0r22 resistors.
Now I go along the string and measure the voltage with my probes kept at the same distance apart. 35mm typically spans across a 5W resistor. I expect 22.?mVdc across each resistor. I find the ones that read the same. Mark them and box them away for future matched pairs/triples/quads.
If I had calibrated resistors that could pass 0.1A to 1A and stay in tolerance I could fairly accurately measure and mark every DUT.
But even 10off 1% 100ppm/C 1r0, gives a 0r1 that can pass upto 700mA and maybe still stays within that 1% accuracy.
I could string the 10 1r0 REF in series and measure them on my Bench DMM, but I could not guarantee much better than ±0.5%. A sort of 10way Hamon divider.
For matching the stringing together works very well.
For absolute accuracy it is rubbish.
Solder a string of low resistance (or not so low) together.
Applied a current limited current to the string.
The lab supply could be set to ~0.1A and apply 4.4V to the string of 20 0r22 resistors.
Now I go along the string and measure the voltage with my probes kept at the same distance apart. 35mm typically spans across a 5W resistor. I expect 22.?mVdc across each resistor. I find the ones that read the same. Mark them and box them away for future matched pairs/triples/quads.
If I had calibrated resistors that could pass 0.1A to 1A and stay in tolerance I could fairly accurately measure and mark every DUT.
But even 10off 1% 100ppm/C 1r0, gives a 0r1 that can pass upto 700mA and maybe still stays within that 1% accuracy.
I could string the 10 1r0 REF in series and measure them on my Bench DMM, but I could not guarantee much better than ±0.5%. A sort of 10way Hamon divider.
For matching the stringing together works very well.
For absolute accuracy it is rubbish.
absolute accuracy gets expensive and difficult to keep up. I don't need that for 98%
that's why I'm enjoying a delta button along with a cheap 22K counts rig.
that's why I'm enjoying a delta button along with a cheap 22K counts rig.
Even with a better meter I would have to get them recaibrated regularly and keep at least two to compare that they are still close to the way they were recalibrated.
Building and keeping instruments to "standards" is not cheap.
Not an area I want to enter.
I have 4 DMM and now and again I compare them just to make sure one has not gone "broken" !
my free DMMs don't even have a battery warning function, the only way I notice is when the voltage is way off, bad tools are a liability to any technician.
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For wire testing: ANSI/NETA ATS-2009 supposedly establishes some basic guidelines:
This is just about the only information I have found for rating regular wire (not wire for household installation or 3-phase wire).
This kinda jibes with what my seller lists on his description of the wire. Though I have some questions to ask him when he gets back from holiday. Specifically strand count (I actually tried ot count for a bit, got lazy and gave up) and if he knows (or can test) the insulation resistance.
This is the information he gives for his 14AWG wire.
As for absolute versus relative accuracy. For many circuits, as long as your device is capable of the precision you need, absolute accuracy is not necessary. Many circuits that get designed need relative accuracy of the parts versus absolute. For example, if you are designing a filter for audio. You seldom care if the knee is 3901Hz versus 3903Hz (obviously an exaggeration). You just want to make sure the cutoff is at the same place on both sides.
This is just about the only information I have found for rating regular wire (not wire for household installation or 3-phase wire).
This kinda jibes with what my seller lists on his description of the wire. Though I have some questions to ask him when he gets back from holiday. Specifically strand count (I actually tried ot count for a bit, got lazy and gave up) and if he knows (or can test) the insulation resistance.
This is the information he gives for his 14AWG wire.
As for absolute versus relative accuracy. For many circuits, as long as your device is capable of the precision you need, absolute accuracy is not necessary. Many circuits that get designed need relative accuracy of the parts versus absolute. For example, if you are designing a filter for audio. You seldom care if the knee is 3901Hz versus 3903Hz (obviously an exaggeration). You just want to make sure the cutoff is at the same place on both sides.
silicon wire from any old place >yeah that HV standard can be the target but how does one verify that goal has been met with certainty? say I want the thinnest insulation possible Eg high performance wire. If they are substituting Al for Cu ..then they obviously haven't got the process controlled for anything else, right!
AND If I keep asking the china shops for HV voltage wire they are going to hand me cable with extra insulation to make it doubly sure leaving some of the conductor smaller >moving targets.
I'm sure with modern machines they can build anything anyone wants and that's exactly what they do, the problem is there is no data sheet with any reputation standing behind it.
AND If I keep asking the china shops for HV voltage wire they are going to hand me cable with extra insulation to make it doubly sure leaving some of the conductor smaller >moving targets.
I'm sure with modern machines they can build anything anyone wants and that's exactly what they do, the problem is there is no data sheet with any reputation standing behind it.
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^sorry for the rant. cut throat prices make poor products...the end. civilization as we know it
it's turned into the hunt for a diamond in the rough, is it getting better? I think so
it's turned into the hunt for a diamond in the rough, is it getting better? I think so
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I just found and ordered these:
www.ebay.com/itm/2PCS-Copper-Gwinstek-LCR-Kelvin-test-clip-bridge-test-clip-Microresistivity-clip-/221893878101
www.ebay.com/itm/2PCS-Copper-Gwinstek-LCR-Kelvin-test-clip-bridge-test-clip-Microresistivity-clip-/221893878101
Yep, those are the ones i am talking about where I mention I paid less for my kit than the clips alone are going for on ebay. They have proven to be very nice clips so far. I have a review I am working on for a microohm meter and these new kelvin clips work GREAT with it.
I guess in hindsight I oculd have at least linked to the eBay sellers for the clips. My seller is supposed to finish his holiday just after x-mas. We will see how quickly he gets them back in stock.
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Hi PedroDaGr8,
I'm definitely interested myself. My Kelvin test leads are too short, so the kit is a perfect opportunity to fix that situation. What would be nice is some silicone wire a bit over a meter in length. That might be an option, to choose how long you want the kit to be.
-Chris
I'm definitely interested myself. My Kelvin test leads are too short, so the kit is a perfect opportunity to fix that situation. What would be nice is some silicone wire a bit over a meter in length. That might be an option, to choose how long you want the kit to be.
-Chris
I beginning to think silicon wire only leaves China in 1m lengths.
I ordered 8 meters and got.wait for it ........8 pcs 1meter long
Once my seller gets it back in stock he can provide you whatever length you want.
Haha that is just lame. I ordered 3.2m of each color of silicone wire and it came in 3.2m lengths which I cut down to my desired cable length. He even states in his store that if you order multiple meters of cable they will come in that length for you to cut to your needs.
that's not funny man
in addition looking all my China purchases anything with a cable is always under 1meter😕
PC ATX power supply - check
IEC power cable - check
soldering iron - check
DMM - check
things that make you go hmmmm
Just a heads up for you and everyone else. He is back, with his store up and running. He said he has a few pairs of Kelvin clips coming in soon so you may want to email him (I think I sent you his email) to ensure you get some. They are still not listed yet, so email or his thread at EEVBlog is the only way to purchase them.
I'm guessing they precut to save time and money. That's the benefit of buying from someone who knows what he's selling. They actually know what and how to sell it.that's not funny man
in addition looking all my China purchases anything with a cable is always under 1meter😕
PC ATX power supply - check
IEC power cable - check
soldering iron - check
DMM - check
things that make you go hmmmm
Edit: Since I now had two more messages (bringing it up to a dozen) asking for his contact info. I have updated the first post.
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thx had a look around. funny thing your guy only lists 1 meter wire too. prices seem high over there which makes it really hard to compare when shipping is tacked on every single item. I'd suggest a big discount on any orders w/ multiple small items?
Hobby King does OK, Infact they've grown huge in a short time with 2 warehouses just in the USA, so I reckon their doing something right.
Quality of their Turnigy (hexTronic) brand wires seems excellent so far.
I'll just have to make do with shorter test leads until they revert their policy
If you click on one of his wire listings it says:
Like I said, he isn't always the cheapest but for the quality of wire (VERY high strand count, tinned copper, silicone cover, 600V rated) it is a very fair price based on what I have seen. I have not checked out the Turnigy wire yet but might in the future. Personally, the trust I have in him is worth paying a bit extra sometimes to know that EVERYTHING I buy is quality.
Hi PedroDaGr8,
Considering what the normal retail is for those, why are there complaints about quality test leads. My only alternative is Keysight (I really like their new hand held DMM leads!). Now it comes down to what I can afford, it is that simple.
Many thanks for introducing his store!
-Chris
Considering what the normal retail is for those, why are there complaints about quality test leads. My only alternative is Keysight (I really like their new hand held DMM leads!). Now it comes down to what I can afford, it is that simple.
Many thanks for introducing his store!
-Chris
just tested my 18AWG Silicon wire purchased from Hobby King
1meter with 1.01Amp 1% measured 33mV 0.1% ~ .033 ohms/meter
which tracks very closely to being Aluminum.
stranded wire tables lists high strand count 18AWG ~ .020 ohms per meter
so unless they (HK or any other China) states "pure copper" assume its Al. BTW they do sell some "pure" grade silicon wire.
1meter with 1.01Amp 1% measured 33mV 0.1% ~ .033 ohms/meter
which tracks very closely to being Aluminum.
stranded wire tables lists high strand count 18AWG ~ .020 ohms per meter
so unless they (HK or any other China) states "pure copper" assume its Al. BTW they do sell some "pure" grade silicon wire.
^err silicone wire
I reckon Al wire is more useful for the HOBBY crowd, RC planes and cars for weight reduction/flex rather than "pure" electrical performance. the cost increase for obtaining pure copper is still good. BTW after some communications after the fact I was informed by HK that lengths longer than 1 meter can be requested in chat dialog once your shopping cart is ready.The takaway is this >if youre buying from ebay or another www place that has "hobby" in the name or products you must confirm never assume youll be getting pure copper!
I reckon Al wire is more useful for the HOBBY crowd, RC planes and cars for weight reduction/flex rather than "pure" electrical performance. the cost increase for obtaining pure copper is still good. BTW after some communications after the fact I was informed by HK that lengths longer than 1 meter can be requested in chat dialog once your shopping cart is ready.The takaway is this >if youre buying from ebay or another www place that has "hobby" in the name or products you must confirm never assume youll be getting pure copper!
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