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 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. 73 Alex ----- Original Message ----- From: "Alex Pummer" <[email protected]> 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 73 Alex On 7/19/2014 4:45 AM, Attila Kinali wrote: On Wed, 25 Jun 2014 14:21:49 +0200 "Bernd Neubig" <[email protected]> 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 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
