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Comment by YetAnotherNick | Hacker News Reader

But there is no reason why 0 tolerance resistor couldn't exist or even being very useful for certain application like voltmeter.

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The reason you can not build a 0% tolerance resistor is the laws of physics. A very high precision resistor can certainly be build but it will never be perfect. Increasing precision has a cost to it. For normal resistors the shape and thickness of the film of resisting material is calculated and the tolerance is mainly dictated by the precision of the manufacturing process. Increasing this precision of the process adds cost. High precision resistors can be trimmed to specification. When you manufacture the resistor with a lower resistance you can use a laser to trim some of the resistive material away. This is an extra step and adds extra cost. While this can be very precise you are limited to what you can measure and there is a limit to that. Also precision is limited by environmental factors like heat, humidity and aging.

That's also how many higher end analog chips are made, just blast it with laser till it fits tolerance. Making a bunch of chips in less precise process then trimming them chip by chip ends up cheaper than going to more expensive processes.

We are saying the same thing. For most applications, 5% tolerance is fine if could be cheaper. But for some applications it is worth the extra cost.

It sounded like you were saying that a 0 tolerance resistor would be worth the extra cost, and the reply is pointing out that a 0 tolerance resistor is not actually possible anyway, and as you approach 0, the cost increases beyond whatever your limit is.

It would seem pretty pointless to try to nail the resistor to within 0% tolerance when the solder bridges, wire that connects them to the circuit will have resistance.

You can get really high precision for a resistor at the silicon level but as for a regular resistor, the most you can do is buy the best TCR value you can and laser trim it to the exact spec. You can also buy hermetically sealed that have extremely low TCR and tolerances but they are expensive as hell and are relatively massive. If you can control the temperature of the board really well, you can hit very precise resistance values but again, expensive and not possible for all applications.

Overall, it's much easier to understand where your noise bottlenecks are in your system and cheap out on the parts that won't contribute to any reduction. Like if your ADC has a bit resolution of only 1uV, worrying about noise at the nano volt is just a waste of money.

> But there is no reason why 0 tolerance resistor couldn't exist

I think the laws of physics is a pretty good reason.

If you want 0% tolerance, you can hand-match.

No-one needs 0% tolerance.

Sure, you can handmatch. If the thermal radiation of your hands wouldn't affect the measurement.

This is actually a real problem with semiconductors. I often need carefully matched sets of transistors and diodes, and a quick and easy way to get them "good enough" is just to measure either a diode or the B-E junction of the transistor with a multimeter in "diode check" mode. I pin the paper strip to a piece of wood and let the temperature stabilise for about half an hour before I start, and only touch the component with the meter probes.

You can try this yourself. With any given 1N4148 you'll see the Vf indication on the meter change as the microscopic current warms the junction up a tiny bit. If the room (and thus the diode) is fairly cold, it can detect the heat from your finger at about 1cm away.

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