[time-nuts] temperature sensor

Tom Van Baak tvb at LeapSecond.com
Sun Jul 20 10:55:23 EDT 2014

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.

  ----- Original Message ----- 
  From: Alex Pummer 
  Sent: Saturday, July 19, 2014 8:22 PM
  Subject: Re: temperature sensor

  close to the inflection point -- which is dependent of the cut, and for ordinary crystal not made for ovenized operation or for temperature sensing,  between +20C° to +28C° -- the frequency versus temperature function for the first 8C° to 15C° bellow and above the inflection point -- the linearity could be as good as 0.03% . The steepness of the slope for certain cutting angle [35° 12"] is almost zero [less than 0.1ppm/C°. By increasing the cutting angle the slope  becomes negative, by reaching 30° 30" it is approx  3.35ppm/C°.
  Going the other way at, 30°05" the slope is +1.0ppm/C°.
  The thermal time constant of an ordinary quartz is in the range of seconds -- up to 10 sec -- since the quartz is in  vacuum -- to keep the mechanical friction to the air out, and the Q high -- the only thermal conduction between the outside world and the crystal are the very thin -- 0.08mm or less -- wires which providing electrical contact
  That is how I remember as Jean Hoerny and me -- yes that Hoerny one of the traitors -- made the first French quartz clock at LIP in Besançon, back in the past century,
  it is enough number there, or should I look for my old note book?, there was a note; we did not needed to grind the quartz to a precise frequency, we measured it and set the divider, that made the production very economical, how much? that remains the secret of LIP.

  ----- Original Message ----- 
  From: "Alex Pummer" <alex at pcscons.com>
  Sent: Saturday, July 19, 2014 6:16 PM
  Subject: Re: temperature sensor

  temperature sensing with crystal is very accurate, but unless the 
  crystal was made for that application --  has a very large time constant

  On 7/19/2014 4:45 AM, Attila Kinali wrote:

On Wed, 25 Jun 2014 14:21:49 +0200
"Bernd Neubig" <BNeubig at t-online.de> wrote:

the time-nut approach for temperature measurement would be to use
a temperature sensor crystal - like the good old Hewlett-Packard guys
did many years ago. If you do not look for ultra-linearity of the frequency
vs. temp response, there are several possible types of crystal cuts
possible. The simplest one is the Y-cut or the slightly rotated Y+5° cut,
which has a slope of about 90 to 95 ppm/K @ room temperature.
Smaller sensor crystals are tuning-fork type crystals, which
come in the same small cylindrical package as normal watch crystals.
For further reading I have attached an application note for such a
crystal from AXTAL.
Do you have any data on the temperature resistance from case to crystal?
The PT100 and NTC sensors have the nice property of having a very good
thermal coupling between the sensor element and the case. But i suspect
that temperature sensor crystals have a very small area that couples
the crystal to the case (in order to get a high enough Q for the oscillator
to work), which in turn limits the speed at which the sensor reacts to
temperature changes.

Attila Kinali

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