[sdiy] resistor temperature coefficient measurement

[Ian Fritz]

Hi Martin --

Interesting result. Thanks for the report.

I usually assume that if a component has a symmetrical +/- tolerance that 
the material composition has components with opposing properties that are 
made to balance.  I imagine you are right that the +/- 50 ppm is meant to 
cover anomalies in production and that most of the time the results are 
much closer.

You might try to estimate your temperature excursion by cooling a carbon 
resistor (or thermistor) of the same physical size.  But even if your 
cooling was closer to 10 degrees the stability is still better than 1 ppm.

   Ian


At 05:42 AM 2/14/2003, Czech Martin wrote:
>Yesterday I thought I could look into the (unwanted)
>temperature dependency of some resistors.
>I took some metal film types out of the box (speced to
>+- 50 ppm) and measured the resistance at room temperature
>and with coolant spray. To my surprise the resistance
>did not change in the first 5 digits, but the temperature
>dropped certainly by 30 degrees C.
>
>Perhaps the +-50ppm spec is the maximum deviation
>that some production lots may have on a bad day
>and the average is much better than this?
>
>Any experiences or comments?
>
>I will do this again with more time.
>
>m.c.