[time-nuts] temperature sensor

Chuck Harris cfharris at erols.com
Sun Jul 20 15:57:24 EDT 2014


A long time ago in one of my excursions into medical electronics,
I was involved in developing a microwave hyperthermia cancer treatment
system that used a quartz thermometry unit to sense the tumor temperatures.

The quartz thermometry unit had optical fibers with quartz crystals (about
the size of a grain of sand) attached to their ends.  Since nothing glowed
when in operation, I presume that the crystals were driven and sensed
by an IR LED/photo diode arrangement.

Fiber optics was used because of the high power microwaves used in the unit..
we didn't want to have to deal with the microwaves affecting the thermometry
units, or vice versa.

I never knew much about how the thermometry unit worked... it was CFE, and
the customer designed the unit and was mum about all details that I didn't
need to know.

I initially thought that it might be a transmission sort of effect, where
the light intensity changed with temperature, but its total lack of sensitivity
to being in a liquid, kind of makes that unlikely.

It seemed to be very fast, accurate, stable, and pretty precise.

-Chuck Harris

Tom Van Baak wrote:
> Hi Alex,
>
> Thanks for this level of detail. Fascinating. Is the fundamental physics behind
> the quartz angle-of-cut well understood, or does this fall into advanced alchemy
> and industrial magic?
>
> I understand about the time constant now. Yes, on the order of a few seconds makes
> sense. Would it be possible to have other mounting techniques that improve
> environmental contact with the crystal?
>
> Do you know of any commercial quartz crystals (say, in the $1 to $10 range) that
> have been optimized for large tempco at room temperature? Or optimized for
> linearity over a large range (e.g., -40 to +40 C)? I was able to test one once, a
> 5x7mm XO, but I don't know any more about it other than it came from Switzerland.
>
> Thanks, /tvb ----- Original Message ----- From: Alex Pummer Sent: Saturday, July



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