Silly resistor values

Some companies purposely don't use a value from the E24 series when requiring

1% accuracy because it tips off the folks assembling the board that you really meant 1% resistors -- when just looking at a schematic, it's not always obvious whether a 1% or 5% part was used. (Personally I try to label things, e.g., 10.0k rather than 10k if I mean 1%... although this is a somewhat imperfect approach since labeling a resistor 100.0k seems wrong as it would imply 0.1% accruacy, but it's not like you're going to label a 5% 100k resistor at 10e1 either...)

There's been some discussion that it makes sense to just stock 1% resistors rather than both 1% and 5% since these days the price difference is pretty negligible -- this was the policy at one Very Big Company I once worked for. (And one of the guys there was the biggest penny pincher you can imagine -- he'd give Joerg a run for his money :-) -- I probably should have paid more attention to him!)

Well, see above. Also note that while IC designers have it drummed into their heads that as much as possible everything should be ratioed with no exact values, in discrete design sometimes 102k really is better than 100k. If you are just worried about ratios, you might as well use E12 or even E6 values, regardless of the accuracy needed.

If you're completely confident your assembly guys won't inadvertently subsitute 5% resistors on you when you mean 1%, I'd say that using 1% E24 values whenever possible makes a lot sense. (Although numerous 1% values don't exist in the E24 line... e.g., 12k, 16k, etc... this web site has a nice chart:

---Joel

Yeahbut... if they really needed 1% parts, maybe they purposefully chose some E48 or E96 values to avoid confusion with 5% or 10% values.

There are some specific lines of resistors where E48 and E96 are available in 0.1%, 0.05% precisions. Digikey stocks many, for example. So just knowing that it's an E48 value doesn't automatically tell you that it must be 1%.

Tim.

[...]

That's exactly the point. I now do nearly all designs in E96. The lone exceptions are surge-rated resistors, current sense and other situations where specialty resistors are required and 5% or 10% really makes a difference in cost. Or when I need carbon types for high pulse loads.

You can't really have precise ratios in discrete designs unless you go to trimmed or specially produced arrays.

Best is if the assembly guys get released part numbers and are never allowed to switch types without at least a deviation signed by engineering. Otherwise they might swap a surge rated 4.7ohms 5% against a regular non-surge rated metal film type and one day ... tssss ... *phut*

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1% resistors are usually made according to E96 range. Making 1% in E24 doesn't make sense because difference between consequtive values is way bigger than 2% (1% down from the bigger value plus 1% up from the smaller one) so your E24 1% set is full of holes. Every 5% resistor fits somewhere in E24 but most of random values won't if you insist on 1%.

That means 332K is a _STANDARD_ value for 1% resistor when 330K is an oddity.

Because it might be 0.5% or 0.1% or something else.

It is not. E24 1% resistor in the BOM is a crime if this value doesn't exist in E96. 332K 1% is a stock item while 330K is not.

See e.g.

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Sort of makes sense. Someone must use 5% resistors, I haven't, ever.

5% have never offered a measurable cost saving. We pay about £3.50, about $5.60, a reel for 5000 E24 1%.

Funny though, this design also uses 10k, 100k and 1M in 1%.

It means the guy that designed the circuit used pots, and tweaked it within a gnat's ass of the spec, then just ohmed out the pots.

Cheers! Rich

I would say that in the UK 330k 1% is standard and ex-stock, 332k 10% is non standard and will take weeks to get hold of.

That's weird and makes no sense.

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Maybe nothing, maybe something, depends on the design. Just because a value is inside the nominal accuracy does not make it a good choice, as you are permanately creating an offset bias. Potentially bad news in say a voltage divider or gain setting network etc. In the cases you just quoted, 102K 1% is outside the spec of 100K 1% which most people would use.

Because that's standard practice these days. Most people will only stock 1% parts (regardless of the actual E range) because they are potentially more useful than 5% or whatever, and probably cheaper and more readily available depending on the source. e.g times when I have specified say 5%, I've had purchasing come back often and say "we can get 1% cheaper, is that ok?"

A lot of people stick with E12 simply by habbit. Actually I'd go as far to say most people, as the majority of designs I see, even today, still use E12 values - usually 1%.

Consolidataing parts in a design is worthwhile, and is often done as a seperate design step.

There can be many reasons. For instance, at my current company for new designs we pick values based on what stock we have and can get, and what parts are in our EDA database (which includes schematic, verified footprint, 3D model, datasheet, internal tracking number etc). Adding new parts is a pain, so we pick what's already available. Almost all of thm are at least 1%, because that is more useful in more designs. E12 values are typically picked as a first choice, simply by habbit, because we happen to have the full range of those in the database, not so with E24 or E96 etc, as parts have just been added "as needed".

Dave.

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332k is weird and makes no sense:) That's why I started this thread.

I think it demonstrates the diference between the US and UK distributors. The UK electronics industry is much smaller that the US.

Although most 1% suppliers include, make, and sell the 5% values in their E24 1% list, they are not technically a part of the list in most cases.

No. The values have a specific purpose.

You are doing a layout, or you are actually claiming to have electronics educational background?

You should know why the values are what they are. Think decades.

Only if you are making a million pieces and were stupid enough to buy at per piece prices.

For anything less than 100 units, the difference is not that great, and I would much rather stock my proto shop with 1% reels than 5% or jeez... you said 10%.

Sorry, but you cannot even find 10% resistors in axial, much less SMD.

1% is also the most commonly purchased in short qty as well, so you are going to find 100 pc bags at a cheaper rate than the "cheaper" resistor because they charge more if they have to pop open a new spool just to give you your 45 pcs of a resistor nobody else ever orders in popcorn quantities.

He did not say 332k 10% There is no such thing.

THREE significant digits. THINK.

Thanks for the URL, Joel.

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Aren't most (if not all) distributors operating worldwide these days?

typo. 332k 1%

Yeah, low voltage cut off point for a battery. 1.05V or 0.95V per cell wouldn't make any difference.

Left Uni in 1975 and spent my early years at STC working on high rel amplifiers to pop at the bottom of the ocean for telephone systems such as TAT-7. I've run my own electronics company since 79.

I prefer to think production. Too many different values is a nuiscence. If I had designed it and need 332k I wold have used 330k and 2k in series, standard values already in the system.

Syd *does* some fine documentation..