[sdiy] Ratio switching!

[Needham, Alan]

~~  > For example a desired 2416.33mV would require (E24) 16.000k ohm and 
~~  > a 5.100k ohm which gives at best a voltage of 2417.06mV error of 0.01661%
~~  >
~~  > Not to bad!
~~Although it will only be as good as the best components in there.  If 
~~you want
~~around 0.01% accuracy, the resistors will have be (and remain at any
~~temperature) 0.01% accurate as well.  There's the catch.
~~
~~Louis

If the resistors are selected by hand using a good meter then surely even resistors sold as 5% would give the reqired accuracy AT THE TEST TEMPERATURE ?
As far as temperature stability is concerned, as long as both resistors show the same characteristic, wouldn't any variation be self-cancelling, both resistors giving,say, +100ppm/C ? (not sure about this bit, it sounds plausible though !)

	Alan

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