Hi All, Thank you for your help and replies.
Today I used a 4060 to time the 32768 Xtal. I had to make a crude amplifier of a BC548, some resistors and capacitors so that the Xtal sinewave would not dampen and "die". In the end after a selection process of caps I wound up with a nice clean 10 V pulse to feed the 4060.
I made the trace very faint so I could get the thinnest of trace and extrapolated the reading to the best of my ability. (I have used a scope for 35 years)
I made the following measurements on the Q4 (÷16) pin
at start 490µS = 2040.82 Hz
after 1 hour 487µS = 2053.39 Hz
after 2 hours 488µS = 2049.18 Hz
Theoretical time should be 488.2µ S =2048 Hz

On the Q7 (÷128) I measured 3.89 mS
Theoretical time should be 3.906 mS =256 Hz

On the Q12 (÷4096) I measured 128 mS
Theoretical time should be 125 mS =8 Hz

I then measured the same on Channel 2 and found the same results. So my measurements are not "skewed" by which channel I used.

I then measured the same on Channel 2 AND probed the acual Xtal with Channel 1 to see if the probe was "loading" the crystal and "slewing" the clock rate. I found that there was no percieved difference in the measurements.

The amplified clock rate and the actual Xtal clock remained at 30.8 µS. through all procedures. (I have to measure this on the 5µS scale)

My conclusion is that I have an error on my 5µS scale.
The Xtal amplified (÷16) on a 4060 is very close to perfect after 2 hours.
The probes do not seem to load the crystal cct. (note that this is not a naked crystal. I do not know what sort of amplifier/oscillator is under the "Black Blob" ).
I am amazed that the Xtal can be cut on a very large scale (millions of wall clocks) and be so accurate.
I'm happy that my scope is reasonably accurate.

I shall buy a 4040 to check timings on the Q1, Q2, Q3 divisions and will report times next week or so.

I hope my maths is correct. It has been a long time.

Cheers
RH

 

Hi, I did the times for Q1,Q2 and Q3 on a 4040 ic
Q1 (÷2) 61µS Theoretical 61.035µS
Q2 (÷4) 122µS Theoretical 122.07µS
Q3 (÷8) 489µS over 2 cycles = 244.5 Theoretical 244.14 µS

Also after 3 hours the clock pulse was 30.5 µS on the 5µS/division scale and 30.1 on the 10µS/didvision scale.

In any case I can safely assume now that the UnTuned garden variety quartz crystal kitchen wall clock is very accurate.

When I pulled apart another wall clock I found an 8pin (555size) chip with the name STP2740CoB The input is still 30.5µS sine wave from a Xtal. The mechanism seems quite robust and I am loath to wreck it. I looked on the internet but could not find a Datasheet for that number. I think this is the oscillator as there is also a discrete 18pF cap. Does anyone know about this chip.

Again thank you all for your input

RH