Silly resistor values

[Raveninghorde]

Whenever I see app notes I have always noted the strange resistor
values used when a value from the E24 range would do just as well.

At the moment I am doing a BOM for a design originating in the US.
Again I note the liberal use of odd resistor values. For example 332k
1%. What is wrong with 330k? Or 102k 1% instead of 100k?

If the value needs to be 102k not 100k why specify 1%?

For production engineering I would always try to use E24 resistors and
always try and mimimize the number of different values.

Is this just a big company attitude that specifies any old vlaue the
calculator comes up with?

 

[Joerg]

[...]

For production engineering I would always try to use E24 resistors and
always try and mimimize the number of different values.

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!)

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.

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.

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

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: http://www.logwell.com/tech/components/resistor_values.html).

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*

 

[Sergey Kubushin]

Whenever I see app notes I have always noted the strange resistor
values used when a value from the E24 range would do just as well.

At the moment I am doing a BOM for a design originating in the US.
Again I note the liberal use of odd resistor values. For example 332k
1%. What is wrong with 330k? Or 102k 1% instead of 100k?

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.

If the value needs to be 102k not 100k why specify 1%?

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

For production engineering I would always try to use E24 resistors and
always try and mimimize the number of different values.

Is this just a big company attitude that specifies any old vlaue the
calculator comes up with?

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. http://www.logwell.com/tech/components/resistor_values.html

 

[Raveninghorde]

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.

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%.

 

[Rich Grise]

Whenever I see app notes I have always noted the strange resistor
values used when a value from the E24 range would do just as well.

At the moment I am doing a BOM for a design originating in the US.
Again I note the liberal use of odd resistor values. For example 332k
1%. What is wrong with 330k? Or 102k 1% instead of 100k?

If the value needs to be 102k not 100k why specify 1%?

For production engineering I would always try to use E24 resistors and
always try and mimimize the number of different values.

Is this just a big company attitude that specifies any old vlaue the
calculator comes up with?

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

 

[Raveninghorde]

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. http://www.logwell.com/tech/components/resistor_values.html

---
******************************************************************
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. *
******************************************************************

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.

 

[Sergey Kubushin]

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.

 

[David L. Jones]

Whenever I see app notes I have always noted the strange resistor
values used when a value from the E24 range would do just as well.

At the moment I am doing a BOM for a design originating in the US.
Again I note the liberal use of odd resistor values. For example 332k
1%. What is wrong with 330k? Or 102k 1% instead of 100k?

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.

If the value needs to be 102k not 100k why specify 1%?

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?"

For production engineering I would always try to use E24 resistors and
always try and mimimize the number of different values.

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.

Is this just a big company attitude that specifies any old vlaue the
calculator comes up with?

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.

 

[Raveninghorde]

That's weird and makes no sense.

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.

 

[Joerg]

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.

Ahm, reality check, 330K/1%:

http://uk.farnell.com/jsp/search/br...lts=true&appliedparametrics=true&locale=en_UK

Exactly one through-hole type and one 0603 size. No 0805. I wouldn't
exactly call that "popular". Both frigging expensive, my clients would
have me flogged if I squandered the BOM budget that way.

The thru-hole part is made by a little company in Northumberland. Ok,
such a device on a circuit board may be of some sentimental value to a
few folks north of Newcastle upon Tyne ;-)

 

[life imitates life]

If the value needs to be 102k not 100k why specify 1%?

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.

 

[life imitates life]

Is this just a big company attitude that specifies any old vlaue the
calculator comes up with?

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.

 

[life imitates life]

and 5% or 10% really makes a
difference in cost.

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.

 

[life imitates life]

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.

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

THREE significant digits. THINK.

 

[nospam]

Ahm, reality check, 330K/1%:

http://uk.farnell.com/jsp/search/br...lts=true&appliedparametrics=true&locale=en_UK

Exactly one through-hole type and one 0603 size. No 0805. I wouldn't
exactly call that "popular". Both frigging expensive, my clients would
have me flogged if I squandered the BOM budget that way.

The thru-hole part is made by a little company in Northumberland. Ok,
such a device on a circuit board may be of some sentimental value to a
few folks north of Newcastle upon Tyne ;-)

Don't think you got the hang of the Farnell (clunky) search engine.

I find 41 330k 1%, in stock, ROHS, not from Newark, fixed resistors (a few
are reels of the same part available singly)

There are only 4 332k 1%, in stock, ROHS, not from Newark, fixed
resistors.

--

 

[David L. Jones]

Ahm, reality check, 330K/1%:

http://uk.farnell.com/jsp/search/br...lts=true&appliedparametrics=true&locale=en_UK

Exactly one through-hole type and one 0603 size. No 0805. I wouldn't
exactly call that "popular". Both frigging expensive, my clients would
have me flogged if I squandered the BOM budget that way.

Ah, no actually, you obviously checked the wrong box!
For 330K 1% there are only two as you say with "1%", but 61 items under
"+/-1%" (typical sorting by parameter trap on these websites):
http://uk.farnell.com/jsp/search/br...lts=true&appliedparametrics=true&locale=en_UK

11 x 0805, 10 x 0603, 5 x 0402 etc

E12 values in 1% are as common as mud, everyone uses them, mostly due to old
habits as everyone has the E12 range drilled into their head.

Dave.

 

[Nick Cramer]

[ . . . ]
this web site has a nice chart:
http://www.logwell.com/tech/components/resistor_values.html).

Thanks for the URL, Joel.

 

[Raveninghorde]

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

THREE significant digits. THINK.

typo. 332k 1%

 

[Raveninghorde]

No. The values have a specific purpose.

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

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

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.

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

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.

 

[nospam]

IME if you order 330k 1% you will get shipped 332k 1%.

I just checked some wired 330k 1% resistors from my stock and the average
value was around 329k5.

I checked SMT 330k 1% resistors from Panasonic and Neohm and got 329k5 and
328k5.

All the 330k 1% resistors I have were made as 330k resistors not 332k.

If you shipped 332k as 330k you waste 2/3rds of your tolerance and would
have to manufacture and test to 0.3%.
--