[time-nuts] Re: 32.768Khz Crystal Trimming

[Dan Kemppainen]

Rick,

Very delayed response...

So, your thought/comment about tempco stuck in the back of my head. This 
little board has progressed to the point where it can measure it's own 
RTCC oscillator against and external 10Mhz ref.

Out of curiosity a very simple oven was slapped together (Leftover 
packaging Styrofoam, a power resistor, aluminum block, masking tape, 
etc.) and the board was cycled up and down in temperature a few times. 
Temp was measured with an onboard temp sensor.

Anyway, assuming the sign convention is correct, here's a quick plot of 
ppm error vs. temperature. It swings about two ppm over the temperature 
range, with a turnover just under 30C. A second order polynomial fit 
appears to do the job nicely (red line).

Nothing stellar of note in this data, and it's probably old hat to many 
here, but still a fun little side experiment.

Dan



On 4/2/2022 3:27 AM, time-nuts-request at lists.febo.com wrote:
> Subject:
> [time-nuts] Re: 32.768Khz Crystal Trimming
> From:
> "Richard (Rick) Karlquist" <richard at karlquist.com>
> Date:
> 4/1/2022, 12:34 PM
> 
> 
> No one mentioned tempco, so I will.  Ideally you should do your
> calibration at a temperature corresponding to the long term
> average in your workshop.  If the crystal is in a piece of
> equipment with a temperate rise, it should be accounted for,
> and then going forward you have to leave the equipment powered
> up 24/7.  The crystal is probably a tuning fork, meaning it
> won't be AT cut.  It may have a substantial tempco around
> room temp.  In which case that old time-nuts insult may apply:
> 
> "congratulations, nice thermometer."
> 
> Rick N6RK
> 
> BTW, I go back 48 years with crystals.
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