[time-nuts] Low CostTemperature sensor

Orin Eman orin.eman at gmail.com
Tue Jan 17 12:46:11 EST 2017

Directly proportional implies a relationship of the form y = c * x where c
is a constant and * is multiplication.  So it is linear.

To call an exponential relationship "directly proportional" would be wrong.

On Tue, Jan 17, 2017 at 1:17 AM, Charles Steinmetz <csteinmetz at yandex.com>

> Tom wrote:
> That article has a major error. Anyone know what it is?
> Well, the author says the reverse current of a diode is "directly"
> proportional to temperature.  This could suggest that he means the
> relationship is linear (the relationship is actually exponential with
> absolute temperature).  But that's not really an *error* -- just sloppy.
> "Direct" does not necessarily imply "linear."  An exponential relationship
> is "direct" in the sense that it is what mathematicians call "injective"
> (every temperature corresponds to exactly one value of reverse current).
> Then, in discussing the LM95235, he says that it can use the
> "collector-emitter junction diode" of a transistor as the sense element.
> Of course, a bipolar transistor has no collector-emitter junction. His
> diagram correctly shows a diode-connected NPN operating in the active
> region (forward biased, not reverse biased as the rest of his article
> discusses) as the sensor for the LM95235.
> Are any of these what you had in mind, or is there more?
> Charles
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