An ETA 252.611 Movement's Temperature Correction Method Unveiled - Page 3

# Thread: An ETA 252.611 Movement's Temperature Correction Method Unveiled

1. ## Re: An ETA 252.611 Movement's Temperature Correction Method Unveiled

Originally Posted by Catalin
I initially thought about that but I doubt it - right now we have two secondary corrections each at half inhibition apart , if we would have a 3rd the logic would be slightly more complex (not to mention that any symmetry would be lost).
I agree about the symmetry breaking, and suspect that you're right. However, in principle, symmetry is not a requirement for a successful scheme, and this would be a possible explanation for the temperature dependence of the primary correction.

2. ## Re: Great work as ever !!!

Originally Posted by DaveM
Very interesting !
I struggle as well

As previously discussed 8 minutes inhibition gives about 2s per year adjustment resolution, which seems sensible.
But this may be slower than the watch thermal time-constant (I doubt if this matters under real-world conditions). So to get over this you could thermal-adjust 3 times as often and 'round up' the 1/3 count errors until they generated a full count.
But in this case I would expect to see (in dwjquest example)
1077 - 1150 +21+21+21 = -10 (ie apart from rounding-error each inhibition makes the same temperature-compensation).

So I cannot see why they do it like this.
I am also surprised that the 'primary adjustment vs temperature' curve is so smooth. My understanding is that it can only have values mutiplied up from 2.01 seconds per year (for 32768Hz xtal).

Can dwjquest tell us
a) Is each data-point the average of several readings ? If so how many.
b) What is the time and temperature-increment when doing the temperature curve ?

Let us assume that the thermal-adjustments are 'fractional-count compensated', say to 1/4 of a primary count. The compensation-resolution is now 0.5s, and this would explain dwj's curve (assuming that it is the average of several readings).

If there is anybody from COSC out there perhaps they ought to offer dwjquest a consultancy contract!
The raw rate is typically an average of 20-30 readings. Three readings are available during each cycle. Thus, the readings are the average over about 7-10 cycles or 56-80 minutes.

The primary correction is an average of about 15-20 data cycles.

The secondary corrections are an average of 8 cycles.

3. ## Re: Great work as ever !!!

Originally Posted by Bruce Reding
...Make it fast enough and you won't have to worry about inhibition not working.
Exactly!

4.

5. ## Re: Great work as ever !!!

Originally Posted by South Pender
So, Catalin, are you saying that the movement cannot run slow within that temperature range? Is that what you mean by "as ETA is set"?
The ETA raw oscillator seems to be set at around 40 seconds / MONTH fast and everywhere in the 'normal' temperature range is at least 10-20 seconds / MONTH fast - so that part can not run slow unless you do very exotic stuff with it ...

The final values after all the corrections CAN be slow ...

6. ## Re: Great work as ever !!!

Originally Posted by Catalin
The ETA raw oscillator seems to be set at around 40 seconds / MONTH fast and everywhere in the 'normal' temperature range is at least 10-20 seconds / MONTH fast - so that part can not run slow unless you do very exotic stuff with it ...

The final values after all the corrections CAN be slow ...
Got it! Thanks Catalin and Bruce.

7. ## Re: Great work as ever !!!

Originally Posted by Catalin
The ETA raw oscillator seems to be set at around 40 seconds / MONTH fast and everywhere in the 'normal' temperature range is at least 10-20 seconds / MONTH fast - so that part can not run slow unless you do very exotic stuff with it ...

The final values after all the corrections CAN be slow ...
This entry on the Sinn vocabulary page is interesting.

Inhibition cycle

Correction interval in quartz movements.

A range of different techniques has been used in different developments to optimize the accuracy of quartz movements. In the past manufacturers tried to produce the quartz as precisely as possible, to grind it or to set the precise oscillation frequency by depositing layers of vaporized gold and then removing it by laser. Today, quartz crystals are ground in such a way to produce a significant gain in the movement. This gain is then measured in each individual movement at room temperature. Subsequently the movement is programmed so that the gain is corrected every one to four minutes (depending on the caliber). The movement is briefly "paused" to compensate for the gain of the quartz oscillation. In quartz chronometer movements there is also temperature compensation. The temperature sensor on the movement plate then helps to determine the current temperature in the watch and to calculate a correction value accordingly. The correction value which is applied once the inhibition cycle is complete is therefore not constant in quartz chronometer movements; rather it is continually adjusted in line with the current movement temperature.

8. ## Re: Great work as ever !!!

I can see around a 0.031 millisecond gain every second.
That happens to be exactly one tick.
One quartz vibration that takes 1000/32768 milliseconds.

Left uncorrected that would add up to 900 seconds per year.

So I think ETA counts to 32767 when counting for a second. And thus ensuring the clock runs fast.
And that way they don't have to select crystals.

All speculation off course!

The end result remains the same: The clock runs fast, and the corrections slow it down.

9. ## Re: An ETA 252.611 Movement's Temperature Correction Method Unveiled

Why not get closer to 2^15 Hz and decide to add or subtract counts?

10. ## Re: An ETA 252.611 Movement's Temperature Correction Method Unveiled

If you only subtract when applying corrections you don't need to have signed numbers. A bit cheaper I believe. Or at that time anyway. They were fighting for every bit at that time.

11. ## Re: An ETA 252.611 Movement's Temperature Correction Method Unveiled

Originally Posted by Hans Moleman
If you only subtract when applying corrections you don't need to have signed numbers. A bit cheaper I believe. Or at that time anyway. They were fighting for every bit at that time.
Honestly I believe it would still be a lot simpler / cleaner to just set the oscillating circuit fast in the all-analog part and then count 32768 ticks ...

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