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Comment by simne | Hacker News Reader

I'm electric engineer by first education, and have more than ten years exp in field.

Must say, in many cases, these numbers are not important, in good schemes acceptable +-10%, so 26 could be 23.4-28.6.

Even more, cheap resistors marks have accuracy +-5%.

Exists precision resistors with accuracy +-0.5%, or even 0.1%, but high precision applications, typically used some very different technologies. For example, are high quality multi-turn variable resistors, laser cut resistivity pads, created with high cost materials or even rare-earth materials.

And many current applications use some sort of very high quality reference, in many cases, based on totally different physical principle, and scheme constantly adjusted with closed loop.

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> Exists precision resistors with accuracy +-0.5%, or even 0.1%, but high precision applications, typically used some very different technologies. For example, are high quality multi-turn variable resistors, laser cut resistivity pads, created with high cost materials or even rare-earth materials.

Most modern resistors are of either a thin-film type, with sub-micron-thin layers of nickel directly sputtered and onto a ceramic body, or a thick-film type, with a metal oxide/ceramic paste applied and baked onto the ceramic body.

The process window is aimed at a target, but binning operations after production are all that separate precision resistors from cheap resistors.

If you sputter on a little too much nickel, or your paste isn't quite as conductive after baking as you hoped, you just sell that one as a 10% or 5% resistor.

If you get lucky, and produce one that is within 0.01% of an E96 resistor (which might even happen while aiming for an E12 resistance!), you sell it as a precision unit.

Agreed that these aren't that important in most modern designs.

Are you miss (one time) programmable resistors? They appear in 2000s and where available to by, but expensive.

I have not tried myself, just don't found case to use them.

And I have few high precision resistors, and even microwave resistors, they very different from cheap film resistors.

Technologies exists different, for different cases, for different pockets.

> binning operations after production are all that separate precision resistors from cheap resistors.

Really? I would have assumed that resistors are so cheap that testing them is more expensive than designing the process up front around the tolerance.

Yup really. Grab some 5% and 1% resistors and measure them with decent multimeter.

You'll find that their values are almost exactly: stated_value+/-tolerance rather than a range of values.

i.e a 100k 5% resistor will be almost exactly either 105k or 95k not some number in between.

Nope. Not buying it. Just pulled a couple of bog standard thick film 100K 1% 1206s and they are measuring at 99.94, 99.96, 100.02, 99.93 kiloohms.

They're probably batch controlled. There is no way every resistor is being tested for compliance given how cheap SMT resistors are.

A single measurement does not a 0.01% resistor make. When you want that kind of tolerance, drift and aging properties are hugely important and the resistor is not going to be constructed the same way as your bog standard $5/reel 1% resistors.

> binning operations after production are all that separate precision resistors from cheap resistors

Absolutely, no.

Cheap resistors not only have low precision of marking. They also suffered from many other issues.

Examples of cheap resistors issues: they have large temperature coefficient; they change resistance permanently on overheat and when under high voltage; they aged fast and this mean, their resistance permanently change; they usually have large parasite inductance and also they usually have coil structure, and under high voltage happen leak between turns.

High voltage, in this case, mean just about 100Volts.

What really need, is to put analog parts into right mode, and to make it stable, for example vs temperature changes.

As electrical contact points and traces could add up to few Ohms, so resistors need not be exact numbers, but few different from range of planned +-these few Ohms.

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