1) Axtal makes a direct temperature sensing crystal, see Bern Neubig's
former note, but since I grew up by learning how do you make one iron
wheel from wood, I tried and used the transistor PN junction method many
times, it works and it is not a which craft to calculate the tree
resistors for the bias the only issue is that the resistors are also
temperature dependent, but you could go around it by using two resistors
one carbon film and one metal film, by selecting the proper values you
could get -- really! -- zero temperature coefficient [ carbon film has
negative tempered coefficient , metal film has positive...] although
every tranansistor is different, the slope of the "curve " , which is
very linear is contant cca 2.2 mV/C -- that is on the visit card of the
silicon -- for much larger range than the crystals, the only larger
disadvantage, that from the crystal you get a high level signal with
changing frequency [ and it is tempting to belive that it is easier to
handle since it is "digital" and from the transistor you get a DC
changing DC which is analog. Of course you have to calibrate one point
of the DC level at known temperature.
2) yes crystal cutting is a kind of black magic, until you do not know
what you are doing, but if you cut a few thousand pieces it becomes very
logical, and fun. Ask Bernd... he did it for very long time...
C) Ask Bernd he knows it better, he is still making his living with it..
73
Alex
On 7/20/2014 7:55 AM, 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 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
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