An ETA 252.611 Movement's Temperature Correction Method Unveiled - Page 2

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

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

Originally Posted by Hans Moleman
Thanks for that dwquest!
Very illustrative. More than thorough.

I struggle a bit with the two temperature corrections.
No doubt this is correct.
But I struggle with the why.

There is no reason to do them early or even in two lots.
And worse: You can only correct for full ticks when you do a temperature correction.
Partial ticks need to be carried forward till they accumulated to a full tick.

A tick being one quartz vibration.

So my guess is that these partial ticks accumulated into the main correction.
And the main correction therefore shows some temperature dependency.
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!

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

Very well done, David! Do you have a graphs for other temps similar to graph 1? Also, as a bit of speculation, is it possible that the 8 minute inhibition period is both a primary and secondary correction?

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

Originally Posted by Catalin
Since the primary-rate-correction counter only decrements then the initial rate has to be set very high so that at any NORMAL temperature the graph is located ABOVE zero - which also means that if you get to very, very extreme temperatures an ETA TC watch will suddenly have a VERY wild precision (but the watch might have MUCH bigger problems from the temperature point of view, and most likely the owner at that temperature will have even bigger problems).
Is the fact that the ETA thermocompensation design corrects in only one direction (i.e., slowing the rate down) something that could be considered a less-than-optimal adjustment process--in comparison, for example, with the Citizen and Seiko TC designs that compensate for both too high and too low a rate? Or is it more the case that the rest of the movement design will ensure that any adjustment will always be in only the one direction (in other words, the movement can never run too slow)? If so, does this introduce problems in everyday use (in the normal range of temperatures)? To a non-technical person, it would seem better to have TC work in both directions.

4.

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

Originally Posted by Bruce Reding
Very well done, David! Do you have a graphs for other temps similar to graph 1? Also, as a bit of speculation, is it possible that the 8 minute inhibition period is both a primary and secondary correction?
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).

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

Originally Posted by South Pender
Is the fact that the ETA thermocompensation design corrects in only one direction (i.e., slowing the rate down) something that could be considered a less-than-optimal adjustment process--in comparison, for example, with the Citizen and Seiko TC designs that compensate for both too high and too low a rate? Or is it more the case that the rest of the movement design will ensure that any adjustment will always be in only the one direction? (In other words, the movement can never run too slow.) To a non-technical person, it would seem better to have TC work in both directions.
I would guess that the ETA design would have been initially a small advantage in having a slightly simpler integrated circuit, but today maybe not so much ...

I would say that today the major limits are:

- non-linearity and eventually aging of non-digital parts (which I still believe that are the reason why we see the almost 5 seconds change with temperature in the primary adjustment); I also believe ETA is perfectly aware of that and that is part of their conservative specification;

- aging of the quartz;

- capacitive (and to a MUCH lover level voltage) changes after battery changes;

- compound error on (fast) temperature change.

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

Originally Posted by South Pender
Is the fact that the ETA thermocompensation design corrects in only one direction (i.e., slowing the rate down) something that could be considered a less-than-optimal adjustment process--in comparison, for example, with the Citizen and Seiko TC designs that compensate for both too high and too low a rate?...
It does not matter whether it corrects in only one direction or both directions. Obviously, both can have the same effects on accuracy. They are equally effective (provided that everything else is identical: quality of the temperature sensors and the accuracy of the pre-programmed lookup tables). Why would not they be?

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

Originally Posted by ppaulusz
It does not matter whether it corrects in only one direction or both directions. Obviously, both can have the same effects on accuracy. They are equally effective (provided that everything else is identical: quality of the temperature sensors and the accuracy of the pre-programmed lookup tables). Why would not they be?
I see what you're saying, I guess, although I must confess that it's not obvious to me just how both can have the same effects on accuracy if the tendency of the movement is to run slow. How can a compensation scheme that only slows down a movement make the appropriate adjustment?

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

Originally Posted by South Pender
I see what you're saying, I guess, although I must confess that it's not obvious to me just how both can have the same effects on accuracy if the tendency of the movement is to run slow. How can a compensation scheme that only slows down a movement make the appropriate adjustment?
Well, as the ETA is set I would say that it will be a problem under -50 C and over +100 C or so ...

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

Originally Posted by Catalin
Well, as the ETA is set I would say that it will be a problem under -50 C and over +100 C or so ...
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"?

11. ## 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"?
Yes indeed. Make it fast enough and you won't have to worry about inhibition not working.

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