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I recently found out that there were at least three different design technologies behind the Seiko Twin Quartz models.
While quartz based watches are extremely accurate compared to mechanical watches they are still not perfect. One of the main reasons for the inaccuracy in a quartz model is because as the temperature changes the oscillation of the quartz crystal varies slightly. This change in oscillation will cause the slight drift in timing.
To compensate for these changes quartz watches will employ some kind of temperature compensation.
In the late 70’s Seiko introduced the twin quartz models and as the name suggests they employ two quartz crystals in the designs.
Five different calibre series were introduced in less than two and a half years. The 99 series first released in August 1978 (9983A), the 92 series released in December 1978, closely followed by the 97 series released in October 1979 (9722A, 9723A). Just under a year later the 96 series was released in September 1980 (9641A). Hot on its heels was the 94 series released in November of 1980 (9441A).
These series use different technologies to implement the thermo-compensation to ensure accuracy.
The 97 series implements this by using two paired crystals with different thermal characteristics. The temperature variation between the crystals are then averaged to provide accurate measurements over a wide temperature range.
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By using this method the yearly variation for the 97 series (9721A, 9722A, 9723A) King Quartz models are rated at +-20 seconds per year.
I have just the one 97 series model, the 9723-8050 King Quartz.
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This is how I had assumed that the Twin Quartz models worked until I read the Seiko Analog Quartz Technical Manual I uploaded in the thread here.
The manual also outlines the way that the 99 series Twin Quartz models work. These models use one of the crystals for the timing accuracy and the second crystal is used to detect the temperature. These two values are then combined in a processor to calculate the correct timing offset.
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This method allowed extremely accurate adjustments with the models achieving the following yearly variations, 9980A and 9983A +-5 seconds (Superior), 9940A 9942A and 9943A +-10 seconds (Grand Quartz) and the 9920A 9921A and 9923A +-20 seconds (inc. King Quartz).
I have a few more 99 series models. First is a 9923-7000 King Quartz.
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Next is a NOS 9943-5020 Grand Quartz.
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and finally a 9983-7000 Superior.
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I do not have specific details on the 92 series (9256A) but as these were rated at +-10 seconds per year I am guessing these were similar to the 99 series design.
The 96 series were rated at +-20 seconds per year so may have a similar design as the 97 series.
The 94 series models were first released in November 1980 (9441A). These models have the two crystals running at different frequencies, 32kHz and 40kHz. The first model (9441A) was rated at +-20 seconds per year but by April 1981 the 9481A was released and rated at +-5 seconds per year and fitted to Superior models.
The only 94 series model I have is the 9441-5010.
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It is clear that during the end of the 1970’s and early 80’s Seiko was rapidly developing the quartz technology and trying lots of different ideas. I find this the most interesting period for quartz watches as there are many unusual designs and a level of quality that is not found in the later mass produced models.
It is a shame that the levels of innovation did not continue and the levels of accuracy that were achieved 35 years ago have not been surpassed. Now it seems the direction is to contact an external source, such as GPS or the various radio signals, to ensure accurate time.
While quartz based watches are extremely accurate compared to mechanical watches they are still not perfect. One of the main reasons for the inaccuracy in a quartz model is because as the temperature changes the oscillation of the quartz crystal varies slightly. This change in oscillation will cause the slight drift in timing.
To compensate for these changes quartz watches will employ some kind of temperature compensation.
In the late 70’s Seiko introduced the twin quartz models and as the name suggests they employ two quartz crystals in the designs.
Five different calibre series were introduced in less than two and a half years. The 99 series first released in August 1978 (9983A), the 92 series released in December 1978, closely followed by the 97 series released in October 1979 (9722A, 9723A). Just under a year later the 96 series was released in September 1980 (9641A). Hot on its heels was the 94 series released in November of 1980 (9441A).
These series use different technologies to implement the thermo-compensation to ensure accuracy.
The 97 series implements this by using two paired crystals with different thermal characteristics. The temperature variation between the crystals are then averaged to provide accurate measurements over a wide temperature range.
By using this method the yearly variation for the 97 series (9721A, 9722A, 9723A) King Quartz models are rated at +-20 seconds per year.
I have just the one 97 series model, the 9723-8050 King Quartz.
This is how I had assumed that the Twin Quartz models worked until I read the Seiko Analog Quartz Technical Manual I uploaded in the thread here.
The manual also outlines the way that the 99 series Twin Quartz models work. These models use one of the crystals for the timing accuracy and the second crystal is used to detect the temperature. These two values are then combined in a processor to calculate the correct timing offset.
This method allowed extremely accurate adjustments with the models achieving the following yearly variations, 9980A and 9983A +-5 seconds (Superior), 9940A 9942A and 9943A +-10 seconds (Grand Quartz) and the 9920A 9921A and 9923A +-20 seconds (inc. King Quartz).
I have a few more 99 series models. First is a 9923-7000 King Quartz.
Next is a NOS 9943-5020 Grand Quartz.
and finally a 9983-7000 Superior.
I do not have specific details on the 92 series (9256A) but as these were rated at +-10 seconds per year I am guessing these were similar to the 99 series design.
The 96 series were rated at +-20 seconds per year so may have a similar design as the 97 series.
The 94 series models were first released in November 1980 (9441A). These models have the two crystals running at different frequencies, 32kHz and 40kHz. The first model (9441A) was rated at +-20 seconds per year but by April 1981 the 9481A was released and rated at +-5 seconds per year and fitted to Superior models.
The only 94 series model I have is the 9441-5010.
It is clear that during the end of the 1970’s and early 80’s Seiko was rapidly developing the quartz technology and trying lots of different ideas. I find this the most interesting period for quartz watches as there are many unusual designs and a level of quality that is not found in the later mass produced models.
It is a shame that the levels of innovation did not continue and the levels of accuracy that were achieved 35 years ago have not been surpassed. Now it seems the direction is to contact an external source, such as GPS or the various radio signals, to ensure accurate time.
