Accutron History from Bulova Publication
(Reprinted from the Bulova Watch Company's 1960 Publication of this title)
NOTE: Old Father Time specializes in repair and restoration of vintage Accutron Tuning Fork watches. We've been recommended by the Bulova Watch Company for Accutron repair for over 25 years. The information shown below has been re-printed exactly as it was published by Bulova in 1960. However, many factors affecting these watches have changed over last 50 years. For information purposes, we've added our experience-based comments to the original text below in order to exhibit those changes or possible inconsistencies later discovered in the original text.
1 The name "ACCUTRON" denotes a man's wrist timepiece, among other Bulova electronic products. It is the first and only watch-size timepiece, including those powered by a battery, which does not use a balance wheel and hairspring. Instead, the ACCUTRON mechanism has a tuning fork as the timekeeping element. The tuning fork is driven with energy from a tiny Power Cell, or battery, by means of an electronic circuit. The vibratory motion of the tuning fork is converted into rotary motion, for turning the time-indicating hands, by means of a simple but incredibly small mechanism.
The outstanding characteristic of the ACCUTRON timepiece, in comparison with traditional watches, is its accuracy of timekeeping. A tuning fork is inherently accurate, unlike the balance wheel and hairspring. Also, having no pivots or bearings, its accuracy is independent of the effects of lubrication and wear. It is this uniqueness which permits the Bulova Watch Company to give a written guarantee of specific accuracy with each ACCUTRON timepiece. This guarantee states that it will not gain or lose more than a minute a month in normal use as a wrist timepiece.
ACCUTRON was conceived, developed, designed and manufactured entirely within the organization of the Bulova Watch Company, Inc. It first made its appearance in the jewelry stores in November, 1960. Unlike many other space-age devices, the ACCUTRON timepiece was devoted solely as a consumer item (at Bulova expense), although it has since been used in many important applications in the United States' exploration of outer space. New applications are constantly being found where its unusual combination of characteristics such as accuracy of timekeeping, tiny size and long running time on a self-contained source of power are advantageous.
Because the ACCUTRON timepiece is so completely unlike conventional watches, many owners have expressed an interest in detailing information that would enable them to obtain the fullest benefits from its use. Part I Characteristics of ACCUTRON, and Part II, Instructions and Hints for the ACCUTRON Owner, have been written for this purpose.
In addition, many owners, while enjoying the advantages of their unique timepiece, want to know more about the scientific and engineering aspects of ACCUTRON. Part III, The ACCUTRON Mechanism -- How It Operates, has been included in this Manual for the technically-minded user.
I characteristics of ACCUTRON
timekeeping -- ACCUTRON vs. conventional watches
The performance of any wrist timepiece is judged by the way it keeps time in actual use. Performance depends upon the extent of the timepiece's immunity to the many disturbing environmental factors encountered in use. The ability to cope with these detracting influences varies considerably from watch to watch. In conventional timepieces it depends upon:
In the ACCUTRON movement, on the other hand, the timekeeping capability is governed principally by the "designed in" characteristics of its tuning fork. Also, since the tuning fork has no pivots or bearings, its timekeeping is free from the effects of lubrication.
A quantitative comparison of the performance capabilities of ACCUTRON timepieces and conventional watches can be made only by laboratory tests, in which identical conditions of operation can be maintained. For such comparisons the Watch Timing Tests of the Official Swiss Testing Bureaus are very useful. Among these tests is one for wrist "chronometers". These watches are regarded as the most accurate conventional watches available. Watches fulfilling the requirements of this 15-day test are awarded individual certificates by the official testing agency. Should a watch meet somewhat closer performance criteria, the award is issued with "mention" for particularly good results. The performance criteria which must be met to qualify for such distinguished awards are shown in Table I. Also shown are the corresponding characteristics of the ACCUTRON movement, as established by design or manufacturing tolerances.
From Table I the relative capabilities of the ACCUTRON timepiece and the best conventional watches, under laboratory conditions, are clearly evident. In normal service, the superiority of ACCUTRON performance is still more striking.
A conventional watch which gains or loses as little as a minute a month in actual use is very exceptional; in other words a "freak". To provide such performance in quantity production would be fundamentally impossible. For ACCUTRON, however, that same minute a month is a maximum error. Achievement of such accuracy is the direct result of the basic superiority of the tuning fork over the balance wheel and hairspring. It is this difference which has made possible Bulova's guarantee that ACCUTRON will not gain or lose more than a minute a month in normal use as a wrist timepiece. This guarantee is a new criterion for judging watch performance.
the effect of position on ACCUTRON
.One of the major factors contributing to the timekeeping accuracy of the ACCUTRON movement is its small and predictable position error. The tuning fork has a basic position error which is completely predictable in amount of direction. Furthermore, this position error is independent of tuning fork amplitude.
When the long dimension of the tuning fork is horizontal, the frequency of vibration is the same, whether the tines of the fork are alongside each other or one above the other. In most ACCUTRON models, the tuning fork is mounted along the 12-6 axis of the movement. Therefore, the rates in dial-up, dial-down, 3-down, and 9-down positions will all be precisely the same.
When the long dimension of the tuning fork is vertical with the times down, which is the 12-down position in most ACCUTRON models, the effect of gravity causes a slightly higher tuning fork frequency. In this position the rate is 5 seconds per day faster than when the fork is in a horizontal position. Conversely, when the fork is vertical with the tines up, the frequency of the tuning fork will decrease, causing a rate 5 seconds per day slower than when it is in a horizontal position. This is the 6-down position in most Accutron models, and is rarely experienced when the watch is worn on the outside of the wrist.
This extremely small position error is taken into consideration in the regulation of ACCUTRON movements at the factory. It is regulated for best timekeeping when worn on the outside of the wrist. It is recommended that when the owner desires to wear his ACCUTRON timepiece on the inside of the wrist (making the 6-down position occur more frequently), it should be regulated 3 seconds per day faster than the original factory adjustment.
the effect of temperature on ACCUTRON
The elements in the ACCUTRON electronic circuit are chosen to provide for reliable performance under temperature extremes from 20 degrees F to 120 degrees F. Outside this range, performance or timekeeping ability may be unsatisfactory. It should be remembered that this will have no effect on operation under normal conditions, since the ACCUTRON timepiece is meant to be worn on the wrist, and when it is, will be within a few degrees of body temperature, even in extreme cold or hot climates.
The effect of temperature on its rate is considerably less than for normal high-grade wrist watches. If removed from the wrist at night, the temperature of the timepiece may change considerably. However, the net effect upon the daily rate is small since the temperature error is small by design, and the exposure to the "abnormal" temperature does not usually exceed 8 hours daily.
the effect of shock on ACCUTRON
The ACCUTRON timepiece, on the wrist of the user, is completely immune to the shocks of gardening, playing golf or baseball, hammering, etc. Repeated blows, directly on the side of the case, can temporarily affect the operation of the mechanism and cause a change in time. However, it is so protected, when worn in a normal manner on the outside of the wrist, that repeated accidental bumping, sufficient to affect the timepiece, is impossible.
Various means have been included in the design of the ACCUTRON movement to minimize the possibility of damage if the timepiece is dropped. The most sensitive parts of an ordinary watch are the pivots on the balance wheel staff. Conventional watches are shock-protected by special spring mountings for the jewels for these pivots. In the ACCUTRON movement, shock protection has been provided by using a shock bridge and stops to limit the maximum movement of the tuning fork tines, and by a guard surrounding the index and pawl jewel fingers.
A shock great enough to break a balance wheel pivot in a conventional "shockproof" watch may, in ACCUTRON, derange the indexing mechanism. Restoring the mechanism to perfect operating condition requires only minor adjustments by the repairman, in comparison with the major operation of replacing a balance staff.
Everything possible has been done to protect the ACCUTRON mechanism from the shocks of normal use. However, like any fine precision instrument, it should be treated with the respect it deserves.
the effect of vibration on ACCUTRON
The ACCUTRON movement, if mounted directly on a vibrating structure or maintained in contact with it, may be affected by vibration. The effect, if any, would depend upon both the frequency and direction of the vibrations. However, the wrist of the user cushions the ACCUTRON timepiece, so that direct exposure to vibrations which can affect the tuning fork is impossible. The use of power hedge trimmers, power mowers, sanders and other such vibrating equipment will have no effect on an ACCUTRON timepiece worn on the wrist.
the effect of magnetism on ACCUTRON
ACCUTRON timepieces are less affected by the magnet fields usually encountered in normal service than are conventional "anti-magnetic" watches. The criterion for an "anti-magnetic" watch is that, when subjected to the influence of a magnetic field with a strength of 60 gauss and then removed from this influence, it shall operate without being affected more than 15 seconds per day. The ACCUTRON timepiece easily meets this specification, changing rate on a few seconds per day.
The ACCUTRON timepiece should not be deliberately exposed to an extremely high strength magnetic field, as in a demagnetizer or a strong permanent magnet, since it is obvious that it would be possible at some level of field strength to demagnetize the permanent magnets on the tuning fork. If an ACCUTRON timepiece is accidentally demagnetized it will stop, and the tuning fork must be replaced or returned to Bulova to be re-magnetized.
the effect of altitude on ACCUTRON
Its rate, like conventional watches, is affected by the changes in barometric pressure associated with changes in altitude. In conventional watches, other effects are so large that rate changes of several seconds per day are rarely noticed. In ACCUTRON, although the rate change with altitude is about the same as for conventional watches, the effects of pressure changes on its performance are more likely to be apparent because of its very small rate of gain or loss.
The ACCUTRON tuning fork will gain at increasing altitudes. Up to about 15,000 feet the effect is to gain 3 seconds per day for each 5000-foot increase in altitude. This effect is caused by the change in density of the moving air column which, in principle, forms part of the mass of the vibrating tuning fork.
This effect does not normally result in any significant problem. The ACCUTRON owner who is permanently located in an area substantially above sea level may find it necessary to return his timepiece to the local jeweler for regulation, to correct for a gaining rate. Temporary exposure, such as in air travel, has a very slight effect. For example, a 6-hour flight at a "cabin altitude" of 5000 feet (which is conventional) would cause an ACCUTRON timepiece to gain 3/4 of a second more than if the owner had remained on the ground at sea level.
jewels in ACCUTRON
The number of jewels in a watch movement has traditionally been, to the consumer, an indication of quality. However, since the ACCUTRON movement uses an entirely new system of timekeeping, there is actually no basis of comparison with conventional watches. As a matter of information, the ACCUTRON movement has 17 points of possible wear, all protected by jewels.
Most ACCUTRON models are of standard "waterproof" construction. The primary purpose of this case construction is to prevent trouble due to accidental immersion and to perspiration, dust, etc. entering the case. Each "waterproof" ACCUTRON timepiece is individually tested before it leaves the factory to assure that it does not leak. Some users wear these timepieces while bathing and swimming. However, deliberate subjection of a fine timepiece to the hazards of such exposure is not encouraged by Bulova. The case construction required to provide protection for activities such as skin diving is somewhat undesirable for normal use because of styling considerations and has therefore not been employed in any ACCUTRON models.
1 Facts About ACCUTRON, Bulova Watch Company, Inc., Copyright 1960, 1964
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