[time-nuts] Another "atomic" clock question

Jim Lux jimlux at earthlink.net
Sun Mar 2 16:09:01 EST 2014

On 3/2/14 1:00 PM, Magnus Danielson wrote:
> On 02/03/14 21:45, Bob Camp wrote:
>> Hi
>> The gotcha is that there are second order temperature effects. If you
>> are going to run the crystal very far off turn, you need to keep it
>> more stable than you might think.
> "hysteresis", "memory effect", "restart of frequency drift"
> Yeah, it puts a limit on how good a TCXO can track-and-compensate.
> I was also considering the use of XOs for temperature sensing, it has
> the benefit that it is relatively easy to sense with resolution, but
> after that frequency/phase measures is in, getting a good temperature
> reading isn't as easy.
> Is there a good temperature-sensing set of modes in AT-cut crystals, as
> I know being used in SC-cut crystals?

There's the scheme which measures the temperature by comparing 
fundamental and third overtone modes of a crystal.

But if you want to measure temperature, a SAW might be one way.  You mix 
the output of a SAW oscillator with a more stable bulk oscillator, and 
count the difference frequency.

Back in the 80s, I worked at a place that made tons of sensors for all 
sorts of things which either measured a SAW resonator, or measured the 
difference between two SAW resonators that were back to back (so their 
temperatures were the same).  The sensor depended on what you did to the 
SAW: bend it, deposit mass on it, etc.

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