Author Topic: Precision Resistors - General Thread  (Read 29027 times)

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Offline TiN

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Re: Precision Resistors - General Thread
« Reply #125 on: January 29, 2022, 10:44:50 pm »
In my setup ground is connected to PE and internally to digital/analog grounds. Typical resistance standards do not have mains power, so they are true floating devices and there is no need for additional grounding to standards here. Different story for high resistance stuff, but DCC bridges typically operate only up to 10-100kOhm max. High resistance story is for another thread.
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Online alm

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Re: Precision Resistors - General Thread
« Reply #126 on: January 29, 2022, 10:47:33 pm »
Wow, that HP divider just boggles the mind!
Indeed! It's from the 1966-04 issue of HP Journal. They were trying to sell the HP 11102A/11103A/11104A/11105A standard resistor that had as distinguishing feature that it had a small adjustment range so you could closely match them. A voltage divider is a possible application, though this looks very expensive. The resistors were only in the catalog for one year. I'm guessing they either didn't sell well or didn't perform as well as they hoped.
 
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Offline 1audio

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Re: Precision Resistors - General Thread
« Reply #127 on: February 07, 2022, 01:54:59 am »
I bought into the idea of using resistance wire to trim the resistors. And bought a roll of Evanohm from eBay. Now that I have it I'm looking at #38 awg bare wire. . . that is 800 Ohms per foot. Now to figure out how to work with this stuff. Any suggestions?
 

Online alm

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Re: Precision Resistors - General Thread
« Reply #128 on: February 07, 2022, 02:29:39 am »
Termination will probably be your main challenge. From what I've read, the only reliable way is to weld it to a compatible material (not copper). This has been discussed on this forum a couple of times. Especially pay attention to the posts by Edwin G. Pettis, who has many years experience working with Evanohm. This thread contains some useful info: https://www.eevblog.com/forum/metrology/manufacturing-custom-high-precision-low-tc-resistors/
 

Offline 1audio

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Re: Precision Resistors - General Thread
« Reply #129 on: February 07, 2022, 03:50:07 am »
It seems I'll be looking for something else for this project. The Evenohm has too much overhead to be useable. Is anyone interested in a full still packaged roll of EvenOhm thats marked =/- 5 ppm TCR?

Edit- I just checked and I have 12 100 Ohm 15ppm TCR Vishay foil trimmers. I should have checked before buying the wire. The trimmers will be the easy solution. I'll make up a little PCB for all the connections.
« Last Edit: February 07, 2022, 04:08:41 am by 1audio »
 

Offline ramon

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Re: Precision Resistors - General Thread
« Reply #130 on: February 07, 2022, 03:40:35 pm »
Is anyone interested in a full still packaged roll of EvenOhm thats marked =/- 5 ppm TCR?

wire diameter?
 

Offline 1audio

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Re: Precision Resistors - General Thread
« Reply #131 on: February 09, 2022, 02:31:44 am »
It says .0095  I think that's 9.5 thousandths of an inch. Its very fine wire. Pay for the shipping and its yours. PM me.
 
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Offline miro123

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Re: Precision Resistors - General Thread
« Reply #132 on: February 09, 2022, 09:35:41 am »
I have few general questions.
1. What are the pre-condition before starting resistor performance test. For example – X % humidity, T=Y C  for at least Z days/months/years
2. Is baking of Vishay precision resistors a good practice? If yes what is the temperature profile?
3. Should I ask for it the Vishay application engineers or somebody already asked?


I’m asking those questions because I’ve ordered 50pcs of Vishay RC02 resistors
 

Offline leighcorrigall

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Re: Precision Resistors - General Thread
« Reply #133 on: February 09, 2022, 01:01:53 pm »
I have few general questions.
1. What are the pre-condition before starting resistor performance test. For example – X % humidity, T=Y C  for at least Z days/months/years
2. Is baking of Vishay precision resistors a good practice? If yes what is the temperature profile?
3. Should I ask for it the Vishay application engineers or somebody already asked?


I’m asking those questions because I’ve ordered 50pcs of Vishay RC02 resistors

Hi Mirco123.

What is your intended use for these resistors? Vishay resistors are excellent, well characterized, and their specifications are met or exceeded. Why not purchase resistors that are already made for your intended design? I suggest Z foil for long-term stability.

Do you mean Vishay's Post Manufacturing Operations (PMO)? If so, what do you expect the PMO to do? If you cannot answer the question, you may want to reconsider asking Vishay to perform additional operations.


« Last Edit: February 09, 2022, 01:07:15 pm by leighcorrigall »
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Offline ramon

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Re: Precision Resistors - General Thread
« Reply #134 on: February 09, 2022, 02:54:54 pm »
It says .0095  I think that's 9.5 thousandths of an inch. Its very fine wire. Pay for the shipping and its yours. PM me.

Thank you, but that wire is waaaay too thin. I learned that on my first spool.

I will pass for the 2nd time, as in fact I already saw that spool on summer last year and was tempted to buy it. But was somewhat able to control my TEA * WSA syndrome. So I only bought him the spools with the diameters (or materials) that I didn't have before. Like a PDAG spool, Nickel (Alloy 200), Constatan (Advance), and a Nickel spool with TCR 5000 for making 5000 PPM/K RTD (not on that picture, that one is in another box).

That seller got the spools from a closed Clarostat manufacturer facility, and there are many nice and special alloys, he even got some tooling for resistor making. The only wire material that he lacks is Manganin but I already got that covered from Europe source (thanks to a noble man who was a precision resistor maker - many years ago - in Italy).


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Offline shodan@micron

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Re: Precision Resistors - General Thread
« Reply #135 on: March 22, 2022, 03:12:09 pm »
Soon it will be sent to "laboratory of national primary standard" with maximum carefully. :popcorn:
After several months my standards been measured precisely by The D.I. Mendeleev All-Russian Institute for Metrology" (VNIIM)

Also results with measurement reports added to Federal traceability database FGIS Arshin.
 :phew:

Now i can use that standards to calibrate somethings...  >:D

UPD: Try translate one of measurement report link .
Original reports downloaded from FGIS Arshin database link.
« Last Edit: March 22, 2022, 08:13:26 pm by shodan@micron »
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Offline miro123

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Re: Precision Resistors - General Thread
« Reply #136 on: March 22, 2022, 05:23:16 pm »
Do you have history of resistors, e.g. measured value, Alpha, Beta from the past?
 

Offline shodan@micron

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Re: Precision Resistors - General Thread
« Reply #137 on: March 22, 2022, 06:49:42 pm »
Do you have history
Sorry, no any historical data, because main source of that toys is "garbage man"/"refining guys". That people usually do not save any documents.
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Offline shodan@micron

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Re: Precision Resistors - General Thread
« Reply #138 on: March 29, 2022, 09:10:30 am »
I'm little bit sadly today, resistors arrived, but now i see: "Russian Meteorologists is a rough boys" they try push documents into a new case as strong as possible... Well, as result inner case filler be damaged :palm:
I forgot to tell them: this case is not meant for anything other than resistors.
A rough level with precision things, into my country sometimes is incredibly high.



Often i remember Armageddon movie https://youtu.be/dEkOT3IngMQ
« Last Edit: March 29, 2022, 09:15:46 am by shodan@micron »
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Offline bsw_m

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Re: Precision Resistors - General Thread
« Reply #139 on: May 20, 2022, 07:47:39 pm »
Teardown of a МРХ wirewound precision resistors.
From up to down, resistive elements from:
1. МРХ 100 MegaOhm 0.05% tolerance.
2. МРХ 100 MegaOhm 0.1% tolerance.
3. МРХ 300 MegaOhm 0.05% tolerance.

The second picture shows the resistors themselves in the same order. For comparison, there is a 100M 1% resistor manufactured by TE: https://www.te.com/usa-en/product-3-1625959-3.html

P.S. these resistors are very stable.
After 30 years from the date of manufacture, all fit into the tolerance with a margin, many with a 2-fold margin.
« Last Edit: May 20, 2022, 08:13:24 pm by bsw_m »
 
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Offline sahko123

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Re: Precision Resistors - General Thread
« Reply #140 on: May 20, 2022, 09:38:54 pm »
Is there any particular reason certain oils are used? Is because of corrosion issues? Or even humidity issues?
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Offline leighcorrigall

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Re: Precision Resistors - General Thread
« Reply #141 on: May 20, 2022, 10:03:13 pm »
Is there any particular reason certain oils are used? Is because of corrosion issues? Or even humidity issues?

Some oils spoil or are corrosive because of contamination. Other factors are heat transfer and high-resistance insulation.
MASc, EIT, PhD Candidate
 

Offline bsw_m

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Re: Precision Resistors - General Thread
« Reply #142 on: May 21, 2022, 12:35:47 pm »
I has measure diameter of glass insulated cast microwire from 100 MegaOhm resistor.
Wire without insulation: 2um  :o
Wire with glass insulation: 14um
Sorry now I cannot take the microwire photo from my microscope when I don't have the photoattachment for my microscope.

P.S.
I try take photo from eyepiece with phone camera. Quality not good, but..
625x magnification.
« Last Edit: May 21, 2022, 01:00:21 pm by bsw_m »
 

Offline TimFox

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Re: Precision Resistors - General Thread
« Reply #143 on: May 21, 2022, 02:09:54 pm »
Is there any particular reason certain oils are used? Is because of corrosion issues? Or even humidity issues?

Some oils spoil or are corrosive because of contamination. Other factors are heat transfer and high-resistance insulation.

Before I retired, we used Shell DialaTM transformer oil for insulating high-voltage supplies.
So far as I could tell, it was basically pure motor oil, with BHT (or similar) added to retard oxidation.
Butylated hydroxytoluene is an anti-oxidant, whose use in food is controversial.
(For high-voltage purposes, it was necessary to pump a vacuum on top of it to remove bubbles.)
 
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