[time-nuts] temperature sensor

Bernd Neubig BNeubig at t-online.de
Mon Jul 21 13:50:21 EDT 2014

Hi Attila, 
sorry, I was out for a week, so I can respond only now.
Unfortunately I have no data about the thermal resistance crystal to case. It's on my agenda since quite a while to measure the time constant.
Tuning fork crystals are in general in an evacuated package, because any atmosphere would damp the vibration dramatically, and would increase the resonance resistance (which already is in the range of 50k to 100k over temperature) severely.
Therefore the thermal connection is mainly through the wires directly to the crystal element.  There is some contribution of thermal radiation from the cylindrical cover to the crystal, but the main mechanism is thermal conduction through the wires.
But as the mass of the tuning fork is so small, it's thermal capacity is small and thus it will react pretty quickly.
I really need to put this test on my agenda.

Best regards

Bernd DK1AG

-----Ursprüngliche Nachricht-----
Von: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] Im Auftrag von Attila Kinali
Gesendet: Samstag, 19. Juli 2014 13:46
An: Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] temperature sensor

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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