Electronics > Metrology

Manufacturing custom high-precision low-TC resistors

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JoeN:
Is there a thread for that?  I tried (title only) search for make/manufacture/custom and resistor/resistors and I didn't see anything.

I remember a thread about a board member that does custom low-TC resistors for metrology applications.  Can a normal person manufacture their own resistors?  I am talking about really good ones, rather than going to Vishay for $50 a pop.  Is that completely impractical?

amspire:

--- Quote from: JoeN on January 27, 2018, 02:03:32 am ---Is there a thread for that?  I tried (title only) search for make/manufacture/custom and resistor/resistors and I didn't see anything.

--- End quote ---
https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg462296/#msg462296

--- Quote ---
I remember a thread about a board member that does custom low-TC resistors for metrology applications.  Can a normal person manufacture their own resistors?  I am talking about really good ones, rather than going to Vishay for $50 a pop.  Is that completely impractical?

--- End quote ---
Edwin G. Pettis is the person you are thinking of.

Can you make your own resistors? Yes and no. It is not easy sourcing good materials to make the resistors. If you can get Manganin wire, it is solderable so you can make decent resistors, but Manganin does have a significant temperature coefficient. The better resistors are made from Evanohm wire. It can only be welded and it takes a lot of skill to do it right. The process of making zero tempco Evanohm wire is not easy, so if you just went and bought Evanohm wire on the Internet somewhere, chances it would also have a significant tempco and possibly drift.

Edwin explains it in great detail in that thread.

zhtoor:
hello,

here is an interesting method for your consideration. (see attached file)

regards.

-zia

ramon:

--- Quote from: JoeN on January 27, 2018, 02:03:32 am ---Is there a thread for that?  I tried (title only) search for make/manufacture/custom and resistor/resistors and I didn't see anything.

--- End quote ---

I searched that same thread some months ago, and I think Zhtoor once asked that question.

But I remember that most of the replies were negatively biased (something like ... don't even try that ... hard to do ... better to buy one, etc ...).

So, if you don't mind, let's make this thread the thread about 'Manufacturing custom high-precision low-TC resistors'. With a possitive attitude. Something like 'it could be done' (... however I will not dare to say that it will be cheap, easy, or how long it will take to make it.)


--- Quote ---I remember a thread about a board member that does custom low-TC resistors for metrology applications.  Can a normal person manufacture their own resistors?  I am talking about really good ones, rather than going to Vishay for $50 a pop.  Is that completely impractical?

--- End quote ---

Well, let's do it. We will not know if we don't try first.

But the very first problem you will find is that no single alloy manufacturer will ever sell the wire spools to a normal person.

I asked every single evanohm manufacturer and they completely ignored my (low quantity) requests. But I was able to find one evanohm spool (actually Nikrothal LX) from some auction site. The specs were really impressive : 3 ppm (from -55 to 25C) and -1ppm (from 25-150C).

I made a simple resistor around a TO3P mica sheet and protected with heatshrink tubing. (The picture shows a very first test version with copper instead of Evanohm that i made when I haven't received yet the evanohm spool)

Once I received the evanohm spool, I made the resistor. As I didn't have equipment to properly test the TC of the DIY resistor I asked TiN for help, and he kindly tested the resistor TCR using his HP 3458A and TEC environment. (Thanks again Tin!)

And the first result was a complete disaster, around 400 ppm. You can still check in his website how that 1.82K resistor compares to a Vishay Z202 10K:

  https://xdevs.com/ramon_res_z202_test1/

I am working on my second DIY resistor on my spare time. It will continue ...

amspire:
Ramon, how did you weld the Nikrothal LX wire to the leads?

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