# [time-nuts] Low CostTemperature sensor

William H. Fite omniryx at gmail.com
Tue Jan 17 15:09:59 EST 2017

```Orin is correct. To refer to an exponential relationship as directly
proportional is erroneous yet people use it that way commonly and everybody
knows what they mean. It just sets the teeth of statisticians like me on
edge.

On Tue, Jan 17, 2017 at 12:46 PM, Orin Eman <orin.eman at gmail.com> wrote:

> 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>
> wrote:
>
> > 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
> >
> > _______________________________________________
> > time-nuts mailing list -- time-nuts at febo.com
> > To unsubscribe, go to https://www.febo.com/cgi-bin/m
> > ailman/listinfo/time-nuts
> > and follow the instructions there.
> >
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>

--
Intelligence has never been proof against stupidity.
```