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Resistor distribution

F

Fred Bartoli

Jan 1, 1970
0
George Herold a écrit :
Neat, Thanks. (I take it those are spitting out 1% metal film
resistors.)


Hmm, how else are you going to make contact to the spinning lead?

Lots of ways. For ex, after a first meas, which you probably even can
infer from the previous bulk value(s) in the batch you go near the final
cut position, then make contacts with a wire/flex/whatever that have to
withstand limited rotation. Or maybe cover the full angle span with a
spiraled conductor, or brush contacts, or... or...
 
F

Fred Bartoli

Jan 1, 1970
0
Spehro Pefhany a écrit :
Spiral grinding of cheap leaded resistors:

http://www.mfrelectronics.com/cut.jpg

If I was them, I wouldn't be talking about the mercury contacts.

And that one is supposed to help the customer build confidence...

http://www.mfrelectronics.com/wel.jpg

Or that one that is just like the machines are in the living room...

http://www.mfrelectronics.com/capping.jpg

A friend of mine that once was in charge at Vishay for solving some
quality issues on a production line for high value resistors (in India
IIRC) told some horror stories that just reminds me some of those pics...
 
S

SoothSayer

Jan 1, 1970
0
carbon film also has a spiral cut.

Not always.
how about carbon, or copper, brushes: two each end so you can make a
kelvin measurement.

Whatever you use cutting is going to cause localised heating so you'll
have thermocouple effects messing with your measurements, for small
resistors you'll probably have to use AC to counter that.


Matching and culling mass production runs of resistor bodies is easy.

They can do (read it) it before coating, terminating and marking, or
they can make it whole, and read it and mark it afterward.

I am sure that for testing lot run values, they use a platinum faced
wiper.
 
F

Fred Abse

Jan 1, 1970
0
Got it, Field's metal. (I assume named after our own John Fields :^)

Nah! He melts at a much higher temperature ;-)
 
S

SoothSayer

Jan 1, 1970
0
"SoothSayer"


** What an idiotic remark.




.... Phil
Yours? Yes, it was... your retarded crack was absolutely an idiotic
remark to make.

You grasp of manufacturing processes rests firmly at nil.
 
G

George Herold

Jan 1, 1970
0
Hide quoted text -

- Show quoted text -

That's cool, Thanks! Looks like about one resistor every second or
two.
So maybe 3x10^7 per year. (I'm still amazed they can make a profit
selling them.)

I wonder how many resistors the average American 'consumes' in a year.

George H.
 
F

Fred Bartoli

Jan 1, 1970
0
George Herold a écrit :
That's cool, Thanks! Looks like about one resistor every second or
two.
So maybe 3x10^7 per year. (I'm still amazed they can make a profit
selling them.)

I wonder how many resistors the average American 'consumes' in a year.

And that one...

I particularly love the "spoon coating" at 3:31
 
S

Spehro Pefhany

Jan 1, 1970
0
George Herold a écrit :

And that one...

I particularly love the "spoon coating" at 3:31

Oh, man. All that touching, touching, touching with those henna and
curry-tainted hands. I think this kind of place only exists because of
historical 40% duties into India and non-tariff barriers such as
military procurement... otherwise the East Asians (especially China)
would put them out of business promptly. Their duty rate now is "only"
18% or so, according to http://www.cybex.in/.


Best regards,
Spehro Pefhany
 
L

legg

Jan 1, 1970
0
I recall one of the local disties back years ago decided to stop
carrying resistors-- their bean counters figured it was something like
80% of their costs for 20% of their volume, and they wanted to
concentrate on high-markup semiconductors. No longer around, natch.


Best regards,
Spehro Pefhany

And the distie???

You've got to get them into the store buying basics, before you can
flog the high-markup crap.

RL
 
S

Spehro Pefhany

Jan 1, 1970
0
And the distie???

You've got to get them into the store buying basics, before you can
flog the high-markup crap.

RL

Z*ntronics.. many, many years ago, before Bill Ford went off and
started Tech-Trek.


Best regards,
Spehro Pefhany
 
G

George Herold

Jan 1, 1970
0
I remember a prof of mine telling a story about how in the 1960's or
1970's he decided to save a bunch of money on 1% resistors by buying a
bunch of 5% (or maybe 10% -- I can't remember) resistors and sorting out
the ones that were close to the 1% values.

What he found was a batch of resistors whose distribution was a bell-
curve-with-holes.  He concluded that the manufacturer had the same bright
idea before he did.

--
My liberal friends think I'm a conservative kook.
My conservative friends think I'm a liberal kook.
Why am I not happy that they have found common ground?

Tim Wescott, Communications, Control, Circuits & Softwarehttp://www.wescottdesign.com- Hide quoted text -

- Show quoted text -

Hi Tim, I’ve heard that story so many times. I wonder if it’s just an
urban legend?
(Has any one every seen for themselves the fabled ‘hole’ in the
resistor distribution?)
Hey I’ve got this old case of carbon comp resistors.
From a physics Prof. (RIP)
http://bayimg.com/kAiCFAaEH

The 4.7Meg drawer had a bunch in there so I measured those.
(4.7 Meg, 1/2 Watt, 10%)

About 30 resistors, values ranged from 4.36 to 4.71
Here’s the data,
http://bayimg.com/LaiCdAaeh

No obvious hole at 4.7... but not much data either.

George H.
 
Hi Tim, I’ve heard that story so many times.  I wonder if it’s justan
urban legend?
(Has any one every seen for themselves the fabled ‘hole’ in the
resistor distribution?)
George H.

Not an urban legend, but............... The manufacturers used to
make the best resistors that they could and then sort them. So you
could end up with a hole in a normal distribution. But as the
manufacturers got better, they had more 1 % resistors than they had a
market for them. So some of the 1 % resistors were sold as 5 %
resistors.

The same thing applies to semiconductors where one can buy say low
leakage diodes in different grades. The manufacturer makes the best
ones it can and then sorts for the higher grades.


Dan
 
G

George Herold

Jan 1, 1970
0
Not an urban legend, but...............  The manufacturers used to
make the best resistors that they could and then sort them.  So you
could end up with a hole in a normal distribution.  But as the
manufacturers got better, they had more 1 % resistors than they had a
market for them.  So some of the 1 % resistors were sold as 5 %
resistors.

Hmm OK, do you have some personal knowledge? So maybe it was only for
a few years that there was a hole in the distribution? (My old
resitor box doesn't have any old 5% ers, Maybe there is no hole in
the 10% R's?)

Seems if you had a excess of 1% resistors then you should lower the
price.

George H.
 
Not an urban legend, but............... The manufacturers used to
make the best resistors that they could and then sort them. So you
could end up with a hole in a normal distribution. But as the
manufacturers got better, they had more 1 % resistors than they had a
market for them. So some of the 1 % resistors were sold as 5 %
resistors.

The same thing applies to semiconductors where one can buy say low
leakage diodes in different grades. The manufacturer makes the best
ones it can and then sorts for the higher grades.

The same applies to microprocessors, and I'm sure memory. As they get
better at producing the parts the yield of the higher speed/lower
power parts goes up. Of course the orders are for what they are. The
two have to match somehow. One can adjust price and specs to get them
in line over the long run but in the short run one goes into battle
with the weapons one has.
 
J

josephkk

Jan 1, 1970
0
Not an urban legend, but............... The manufacturers used to
make the best resistors that they could and then sort them. So you
could end up with a hole in a normal distribution. But as the
manufacturers got better, they had more 1 % resistors than they had a
market for them. So some of the 1 % resistors were sold as 5 %
resistors.

The same thing applies to semiconductors where one can buy say low
leakage diodes in different grades. The manufacturer makes the best
ones it can and then sorts for the higher grades.


Dan

Suddenly, i suspect that this was/is a short term stopgap method to ship
sufficient quantity of the tighter tolerance units used by various
manufacturers as they got their processes under better control.

?-)
 
T

Tom Del Rosso

Jan 1, 1970
0
John said:
Most 1% or better surface-mount resistors are laser trimmed. You can
check them under magnification and see the trim cuts. If it's done
very quickly, the mean could well be a bit off for any given reel.

But even if the mean is off, they are still in tolerance, right?
 
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