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Metal film resistor stability over time

Discussion in 'Electronic Basics' started by Bill Bowden, Oct 24, 2005.

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  1. Bill Bowden

    Bill Bowden Guest

    What resistance change can be expected over time using 5% metal film
    1/4 watt resistors?

    If I select a couple 5% metal film resistors to use in series to get a
    close 1% value, how stable will the resistor value be over a couple
    year period?

    Are 1% resistors more stable in terms of resistance change over time
    than 5% metal film resistors?

    Thanks,

    -Bill
     
  2. Dan Hollands

    Dan Hollands Guest

    resistance change over time is generally not a concern unless the resistor
    is stressed by overheating. Some data sheets do give informaion on this.
    Generally of much more significant concern is resistance change with
    temperture. If have circuit that requires a stable resistance but is used
    in an environment that has large temperature changes the changes due to
    temperature far exceed the change due to time. Again data sheets define
    temperature stability. High stability costs more money.

    The cost between 5% and 1% metal film these days is negligable for most
    applications Why not just by 1% instead of going to the trouble of selecting
    5%. Are you sure the measuring instrument you use to measure the resistors
    is accurate to 1%?

    Dan

    --
    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
    585-872-2606

    www.QuickScoreRace.com
     
  3. Guest

    While I can't answer your question in specifics, I worked in a CRG
    (customer returned goods) dept. for Collins Radio, where we had a lot
    of older equipment come back for repair. The one trend I noticed is
    carbon film resistors tended upward over time (and with internal
    heating), sometimes quite a bit over their rated value.

    If you're the same gentleman that runs the hobby circuits website,
    thank you. Lot of good stuff in there.
     
  4. Guest

    While I can't answer your question in specifics, I worked in a CRG
    (customer returned goods) dept. for Collins Radio, where we had a lot
    of older equipment come back for repair. The one trend I noticed is
    carbon film resistors tended upward over time (and with internal
    heating), sometimes quite a bit over their rated value.

    If you're the same gentleman that runs the hobby circuits website,
    thank you. Lot of good stuff in there.
     
  5. Jasen Betts

    Jasen Betts Guest

    It's possiblle that the 5% resisters are made while the guy is
    adjusting the machine to the 1% accuracy needed to make 1% resistors :)

    OTOH the metallic material in the 1% units may have a better temperature
    coefficient.

    if thermal stability is not an issue the 5% kludge may be sufficient,
    but otherwise use 1% parts.
     

  6. I serviced some Rockwell/Collins C-band equipment that ran so hot
    that the fiberglass turned black over a large part of the PC board
    because there wasn't enough airflow. The equipment was used in a 65
    degree room, yet the cases were warm to the touch. The didn't use any
    fans to circulate air inside the aluminum box, and it caused lots of
    damage.
     
  7. John - KD5YI

    John - KD5YI Guest

    http://www.vishay.com/resistors-discrete/metal-film/related#technt

    Get the "Resistors - General" PDF document near the bottom of the page. I
    looked at the document examples briefly and they did not indicate that 1% or
    5% tolerance had any effect on long term stability. Temperature over time
    apparently has the greatest effect regardless of initial tolerance.

    Disclaimer: I only read part of it.

    Cheers,
    John
     
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