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Resistor distribution

Discussion in 'Electronic Basics' started by George Herold, Jan 8, 2013.

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  1. I was killing some time last night before going to my first maker
    space meeting, watching some Dave videos.

    http://www.eevblog.com/2011/11/08/eevblog-215-gaussian-resistors/
    http://www.eevblog.com/2011/11/14/eevblog-216-gaussian-resistor-redux/

    In the first video Dave finds that some Philips resistors have a ~
    +/-0.5% distribution right around the ‘correct’ value.

    In the second he finds that some cheaper (Xicon?) also have a 0.5%
    ‘spread’, but the average is a bit (~0.35%) lower than nominal.

    This raises a bunch of interesting questions.
    Do any resistor makers publish this sort of data?
    Does buying resistors from a ‘better’ manufacturer lead to resistors
    with a better mean.
    I use mostly cheap Xicon 1%ers. A few times I’ve gone hunting through
    the parts bin with an ohmmeter trying to find some particular value.
    Though I don’t have any data I did strike me that the average seemed a
    bit low. (When looking for a 10.0k ohm I found many more 9.9X k ohms
    than 10.0X k ohms.)

    So does anyone know how 1% resistors are made? I find it hard to
    believe that they trim each one.
    (Do they trim the 0.1% ers?)

    George H.
     
  2. OK Thanks, I guess I can believe the trimming, but do they measure
    each one?

    George H.
     
  3. I could imagine that they measure a few to set the laser cut and then
    only do spot checks. But I clearly have no clue how it's done!
    It sorta blows my mind to think someone can make it, measure it, trim
    it, and then sell it to me for under a penny.

    George H.
     
  4. Well I scrapped the silk screen off the surface of a few and an L cut
    was exactly what I saw.

    I think there is a Vishay resistor plant somewhere near me... I wonder
    if I could get a tour?

    George H.
     
  5. Fred Bartoli

    Fred Bartoli Guest

    Michael A. Terrell a écrit :
    Selling too?
     
  6. Jeroen

    Jeroen Guest

    Sort of: Droids.

    Jeroen Belleman
     
  7. Guest

    More like six to a penny.
     
  8. Guest

    Have you ever seen an operation like DigiKey? ...or Amazon? ...or
    NewEgg? Do you really think they have people chasing parts?
     
  9. amazon sure has people doing the picking.
     
  10. Robert Baer

    Robert Baer Guest

    Back in the "good old daze" '70s to '90s) 5% carbon comps ran
    typically 2% high with a rather tight spread - maybe +/- 1% (to +/- 2%
    at most).
     
  11. Guest

    The video I saw was all automated.
     
  12. Hey, I was scraping the blue coating off some through hole MF's
    Do they laser trim those too, or something else?
    I couldn't see much, but when I was done, 10k had become 10.5k.
    (I could do in circuit, tweaking with an exacto knife.)

    George H.
     
  13. Interesting, Don't CC's have a terrible tempco. (We used them as low
    temp sensors, maybe better near RT.)
     
  14. 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.



    Best regards,
    Spehro Pefhany
     
  15. 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
     
  16. 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?

    (there's some indium gallium... ? tin? alloy that melts below 100C.)

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

    George H.
     
  17. oops.. nope it is indium gallium and tin... Galinstan.

    Geo
     
  18. Robert Baer

    Robert Baer Guest

    The more modern Ohmite carbon comps were about 5 times better that
    the really old ones that had the leads spiral wrapped around the ends..
    The 47 to 100 ohm Ohmites were very nice as fuses / overload
    indicators when placed in the cathode of series power regulator tubes.
    Discoloration "level" would indicate a certain amount of overload,
    and next cracking to open, and then carbonizaton and finally "busted black".
     
  19. Phil Allison

    Phil Allison Guest

    "George Herold"

    In the first video Dave finds that some Philips resistors have a ~
    +/-0.5% distribution right around the ‘correct’ value.

    In the second he finds that some cheaper (Xicon?) also have a 0.5%
    ‘spread’, but the average is a bit (~0.35%) lower than nominal.

    This raises a bunch of interesting questions.
    Do any resistor makers publish this sort of data?


    ** The tolerance percentage includes a nominal service life - so a nominal
    1% tolerance part is usually much tighter when new. That is all that is
    being claimed.

    Does buying resistors from a ‘better’ manufacturer lead to resistors
    with a better mean.

    ** Pointless even reseching it as it would be a moving target.


    So does anyone know how 1% resistors are made? I find it hard to
    believe that they trim each one.


    ** That spiral cut does not get there by itself and the cutting machine
    stops when the value is right.

    Tighter tolerances ( than say 1%) requires slower operation and or the use
    of a laser - so the parts cost more.


    ..... Phil
     
  20. Jasen Betts

    Jasen Betts Guest

    carbon film also has a spiral cut.
    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.
     
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