How "Zero" is this supposedly Zero-TCR resistor? And how much better is it than this other one?

Question

I found a resistor at Digikey, and the TCR was quoted as being 0.0ppm/°C, and I had to check the datasheet just to refute my suspicion that it was a data entry error, and it looks real, but just how real is it? Has anybody used one of these, and measured the TCR and so can confirm this specification, or at least that you have used one of these? Here's the resistor:

1K ±0.1% Non-Inductive Metal Foil Through Hole Resistor (Datasheet: VPG Foil Resistors # Y00781K00000B9L, Digikey # 804-1061-ND). It has a "high" price of about $81.93 as of Feb. 19, 2024.

Please contrast with (Datasheet: VPG Foil Resistors # Y16311K00000T9R, Digikey # Y1631-1.00KACT-ND) having a ±0.2ppm/°C TCR but similar specifications and a $10.84 price: 1 kOhms ±0.01% Chip Resistor Non-Inductive Metal Foil.

I ultimately want to measure the efficiency of small buck, boost, and inverting power converters, including the boost Joule Thief, and the buck joule thief I came up with, and somebody else invented as well, but also the other ones that I study.

But if my application isn't rigorous enough to be relevant to this question, please throw out my idea of how to use it, and please tell me anyway about the metrology applications of these two resistors, and how much better the one is than the other. I'm sorry if this is not specific enough for you, but I'm sure that I will want to measure resistors, or my own custom-made, non-inductive, wire-wrapped resistors, or something else yet to be invented.

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Edit 1:

Responding to a commenter, my question is regarding the advertised specification on the Digikey website as shown at the bottom of the screen shot below:

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See also the statement of essentially zero TCR on the data sheet:

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Edit 2:

Mattman944 commented:

Do you really need this precision? Realize that most engineers will go through their entire career without needing a resistor this precise.

Here's my reply:

I am insatiably curious, and really want to learn this stuff. If you could answer the question please that would be great, otherwise the specifics have already been given in the question, and that was to prevent an extended chat, which is what we'll get if you ignore my question. Please search for the word "sorry" in my question, and read that section again, thank you. Isn't this a good question? Shouldn't other engineers know the answer to this question? I'm not the sole audience. Avoid extended chat and answer the question, please!

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Edit 3:

Nobody was able to see past the example application I gave of measurement of small power converters. Since I still want to understand this, I am adopting a new project for the sake of this question:

Please disregard my former project. Instead, I'm performing the microcalorimetry measurement of real-time heat-related battery degradation to certify batches of Li-ion cells in various capacities for customers according to important work that Jeff Dahn. pioneered... in order to start a company and pay several EE salaries. Both very high precision and accuracy are required. Metrology class components are now justified.

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Edit 4:

Spehro Pefhany commented:

Batteries change capacity by perhaps 0.5%/°C (5000 ppm). I don't see how you could justify the need for sub-single digit ppm with that kind of temperature dependency. I've been involved in a couple projects where it was actually justified, mostly because the force involved was so weak (gravity).

My reply:

That is an outdated method of predicting cell lifetimes debunked in this video by Jeff Dahn, an outdated method that failed Nissan in their Leaf EV, a tragic 37% capacity loss in 2 years, as stated in the class-action lawsuit filed in Southern California and Arizona about the "Thermal Management Defect". To predict cell lifetimes for an EV in hot Arizona, one must measure the heat of the parasitic chemical reactions going on inside the cell -- for instance, they consider 100uW to be very bad. To measure quality cells (additive soup effectiveness), they first used a microcalorimeter having a sensitivity of 10nW, and a baseline stability of 500nW per month, with which they now accurately predicts cell lifetimes in weeks vs years. All this in the linked video which IMHO every EE who deals with Li-ion should watch, and know.

Answer 1

if my application isn't rigorous enough to be relevant to this question, please throw out my idea of how to use it, and please tell me anyway about the metrology applications of these two resistors,

These resistors arise in applications where analysis of system performance substantiates their specifications. They are used when you design the system and it turns out that unless the resistors are this good, it won't work. Not the other way round.

That's a whole lot of different applications. In fact, you could write an entire book about how such resistors are applied in practice. The question lacks focus.

[please tell me] how much better the one is than the other

One has TCR of 0.0ppm/K. Taking rounding into account, that reads 0.0±0.05ppm/K. The other has TCR of 0.2ppm/K, and that reads 0.2±0.05ppm/K.

Worst case, the "better resistor" has 0.15/0.05=3x lower TCR than the "worse" one. Best case, the "better" resistor has 0.25/0.01=25x lower TCR than the "worse" one. That's just from marketing figures. Once you look at the specs in the datasheet, you'll see that the actual ratio at 25°C is within that 3-25x range.

What puzzles me is that you're trying to presumably use such resistors, but lack the ability to understand their datasheets. I claim that until you can read the entire datasheet and explain it to a 6-year-old without missing any critical details, you don't know nearly enough to use those resistors for anything other than display pieces.

It has a "high" price of about $81.93

Given their performance level, that's dirt cheap. Try making one of those resistors yourself for less than say $10k in time, materials and equipment. You'll spend about as much just renting the test equipment needed to measure the performance of your homemade resistors.

I ultimately want to measure the efficiency of small buck, boost, and inverting power converters, including the boost Joule Thief, and the buck joule thief I came up with, and somebody else invented as well, but also the other ones that I study.

TCR of those resistors is about 2 orders of magnitude beyond what you reasonably need. You don't need to measure the efficiency of those converters with more than say 0.05% resolution, and 1% accuracy. You'll be comparing one to another, so absolute accuracy isn't of much concern, as long as it doesn't drift too much over time and temperature. I doubt you'll be moving your test rig from room temperature to a sauna, right?

If the rest of the circuit doesn't cost more than the resistors, then probably you don't need those resistors. If the circuit is cheap, then it will perform poorly enough that the resistors won't make a difference. Precision costs money, generally speaking. To benefit from these resistors' TCR, you need to do a lot of work elsewhere in the circuit so that it is accurate enough to benefit from low TCR resistors. Even just to measure the TCR ±5°C around room temperature, you'll need a multimeter that costs 2 orders of magnitude more than one of the resistors, never mind a decent thermometer, and metrology knowhow.

In other words: you're hung up on one catchy spec of just few parts in the circuit, where you should be looking at system performance, and specifying that. Without system specs (none appear in the question), it's pointless to talk about TCRs of just a few components.

Answer 2

The data sheet says:

Absolute resistance change (window):
VHP100 <60 ppm (–55°C to +125°C)
VHP101 <10 ppm (+15°C to +45°C)

Not zero.

Answer 3

They provide curves of the TCR that show you it's not only not zero but has a characteristic concave shape typically. About 0.3ppm/K. Metrology level, but not zero.

Measuring efficiency of a converter is unlikely to require anything much more precise than a fraction of 1%, 0.1% would likely be overkill.