US1906985A - Vibratory frequency standard - Google Patents

Description

May 2, 19330 w. A. MARRISON VIBRATORY FREQUENCY STANDARD Filed NOV. 23, 1928 vvvavmn W A. MARR/S'ON BY Q97 T W A TTURNEV Patented May 2, 1933 UNITED STATES PATENT oFFicE WARREN A. MARRISON, OF MAPLEWOOD, NEW JERSEY, ASSIGNOR TO WESTERN ELEC- I TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK Application filed November 23, 1928.

standards, depend, as is well known, on the material of which they are made, and on their physical conformation.

From one point of view, to the extent that the properties of the supporting base enter into the situation the vibratory element has effectively added to it amass of less refined material to the detriment of its function as a frequency standard. Further in the ordinary case the base itself contributes nothing to the vibratory element, if considered as a part thereof, except a lumped mass, which functions to a large extent as an energy absorbing or damping means, with a resultant deleterious efiect on the decrement of the ele ment. In particular if the mass of the support is variable, as maywell happen in practice, there tends to result a corresponding direct variation of the frequency of the element, as well as of other properties affected by the support which more indirectly affect the frequency stability. Of course invariableness of the characteristics of such elements in any way affecting the frequency is a prerequisite when such elements are used as frequency standards. The decrement of a vibrating means is related to its frequency characteris tics and is included in the same category in the above consideration.

The application of the above principles requires that the vibratory element be made as functionally independent of its supporting means as possible, as by effective dynamic isolation, although, probably on account of lack of appreciation of the basic phenomena involved, the practise, it is believed, has been inconsistent with this point of view.

7 It is an object of the invention to improve the frequency characteristics of a vibratory frequency standard and especially to effect an increased frequency stability, and a decreased decrement, thereof.

It is a further object of the invention so to mount the vibratory element as effectively to isolate it dynamically from its support, and as to insure a minimum interchange of VIBR.ATORY FREQUENCY STANDARD Serial No. 321,449.

vibratory energy, or reaction, between the element and support.

In a practical embodiment, using a tuning fork as the vibratory element, the fork at its base is connected to its support by a. flexible mounting member. lVithin the scope of the invention this member may assume any one of a variety of forms. In a particular instance it consists of a U-shaped structure of thin elastic sheet metal attached to the tuning fork base at its middle portion and to the support by outturned end portions of the legs.

While the mode of vibration of vibratory frequency standards now used approximates very closely simple harmonic motion, since they simulate very highly selective circuits in their ability to respond only to a single component among those impressed upon them either electrically or mechanically, it has heretofore been difficult, without excessive elaboration of detail, to translate the harmonic (sinusoidal) mechanical vibrations of such a standard into a corresponding type of electrical variation.

Applicant has, however, by use of simple and inexpensive means, been able to correct the distortion in the generated wave, as meas ured by its divergence from a pure sinusoid. He has also been able to improve the form of the immediately generated wave, as compared with the result of prior practice, or to accomplish the optimum result secured by prior practice by less iaborate and expensive means. Accordingly the accomplishment of these aims comprises further objects of the invention.

The correction of the wave form is accomplished by applicant by use of the compensating principle, using an electrical translating device whose impedance characteristic is such as to introduce a complementary or com pensating distortion to the wave impressed on it from the vibratory element. 7

The means for improving the generated wave form involves new mode of presenting the pick-up or generator coils to the vibrating element, namely inserting such coil in a slot or opening of the element.

The use of either of these two expedients,

namely, that of correcting the wave-form or of avoiding distortion in the generated wave,

in combination with the flexible mounting,

insures the production of an electrical wave 5 of great purity of form and one which has a very stable frequency.

In the drawing, Fig. 1 shows one method of supporting a vibrating element to avoid dynamic coupling to the supporting member, and a method of associating the vibrating element with an electrical amplifying circuit adapted to pick up energy from, and to feed back energy to, the vibrating element. The circuit shown may also be adaptedto com- 15 pensate any lack of symmetry in the voltage applied to it;

Fig. 2 shows another type of mounting for nonreactively associating a. vibrating element with a supportin member;

Fig. 3 is a grap showing the current lotted against time in the output circuit the space dischargg device having the characteristic: curve of ig. 5, if a sine wave were impresed upon the input electrodes of the device;

Fig. 4 is a graph of voltage plotted against time of an unsymmetrical wave which may be impressed on the input circuit of the first space discharge device of Fig. 1 to be resha ed therein;

ig. 5 is a graph showing the characteristic curve of a space discharge device designed to rovide a compensating distortion to a wave 1m ressed upon it from a pick-up coil associa d with a mechanical vibratin element in a manner such as that shown in i 1, that is, where the flux which is cut by t e turns of a stationary coil in which an electromotive force is induced, does not vary with respect .to time symmetrically about its mean value.

It also shows a distorted wave about a vertical axis as an input wave to, and a compensated sine wave about a horizontal axis as an output wave from, such a device; A -Fig. 6 shows an elevation of a mechanical vibrating element having an electrical (pickup coil mounted in an aperture in sai element;

Fig. 7 is a crow-section of Fig. 6 across the center of the ick-up coil showing also a winding for app ying a polarizing potential to the core on which the pick-up coil is wound; and

Figs. 8 and 9 are variations of Fig. 7, Fig. 8 showing an arrangement in which the core on which the pick-up coil is wound is reduced in diameter through the vibrating element to accommodate a greater number of turns across the portion of greatest flux density, and Fig. 9 showing an arrangement whereby the flux is concentrated across the narrower section ofthe vibrating element, so that the pick-up coil may be narrower without decreasing the electromotive force induced therein.

In Fig. 1 a supporting member 1 has attached thereto by means of screw 2 a flexible mounting member 3. Attached to the flexible mounting member 3 by means of screws 4 is a tuning fork or other mechanical vibrating element. 5 of ma etic material. Inductively associated with the tuning fork 5 is a pick-up coil 6 which is connected to the input electrodes of a three-electrode space discharge device 7 which acts as an amplifier. Connected across the grid and filament of the space discharge device 7 in series with the pick-u coil 6 is a battery 8 adapted to apply a esired ne ative potential to the grid of the device. onnected across the output electrodes of the device, in series with space current battery 9, is a driving coil 10 adapted to maintain the tuning fork in vibration with a portion of the energy in the output circuit of the space discharge de- 735 vice. Coupled to the space discharge device 7 by means of condenser 11 is a second threeelectrode space discharge device 12. Across its input electrodes is a battery 13 and resistance 30 designed to apply a desired polarizing potential to the grid thereof. Across its output electrodes is the primary of a transformer 13 in series with a space current battery 14. The filaments of the tubes 7 and 12 are heated by means of batteries 15 and 16 in series with rheostats 17 and 18 respectively.

In Fig. 2 a flexible mounting element 19 connected to a supporting member (not shown) has attached thereto by means of screw 20 a tuning fork or other mechanical vibrating member 21.

The flexible mounting elements 3 and 19 of Figs. 1 and 2 respectively may be made of thin elastic sheet metal or other suitable material having a high degree of flexibility in proportion to that of the supporting member or the mechanical vibrating element. In Fig. 1 the mounting element may be a sheet of metal as above described and the vibrating element may be attached thereto perpendicular to its surface. In Fi 2 the mount ing element is U shaped an is attached to the vibrating element at. its middle portion and adapted to engage a supporting member by outturned end portions of the legs. In both cases the mounting element is designed to provide a minimum of mechanical coupling between the vibrating element and the supporting member.

The flux cutting the turns of a stationary pick-up coil due to a mechanical element vibrating in juxtaposition thereto, as in the manner illustrated in Fig. 1, is a function of the air gap between the coil and the vibrating element, and as this air gap is a constant gap plus a variable gap, it follows that the flux does not var symmetrically about its mean position vs no with respect to time. The rate of change in flux, which determines the electromotive force generated, 13!

correspondingly is not symmetrical with respect to time but is greater at the instant the air gap is a minimum than a half cycle later when the alr gap 1s a maximum.

A typical electromotive force wave that would begenerated by an arrangement like that of Fig. 1 is shown at 23 in Fig. 4. If this wave is applied. to a space discharge device whose space current characteristic over the operating range has a curvature opposed to that of the fork the resultant will more nearly approach a sine wave, and a complementary distortion may thereby be introduced.

This is illustrated in Fig. 5 in which an undulating wave 23 shown plotted about a vertical time axis and having negative half cycles of greater amplitude than its positive half cycles is assumed to be applied. to a space discharge device having a characteris tic curve 24 as shown, in such a manner that the negative half cycles are amplified less elfectively than the positive half cycles, "to yield a resultant current wave 25 in the output of the device, which is substantially of sine form. The choice of on which waves 23 and 25 are plotted easily lends itself to graphical treatment in the determination of the exact form of the resultant wave In the circuit shown in Fig. 1 space discharge device 7 may have a desired characteristic curve such as that shown in Fig. 5 by suitably proportioning and associating its elements and applying the proper voltage to its electrodes. The wave to be amplified may be applied at the proper point on the characteristic curve of the tube by varying the grid polarizing battery 8 or in any other manner desired.

The voltage induced in a coil by a magnetic element is proportional to the number of turns in the coil and to the rate of chan e in the density of the flux cut by those turns. If a pick-up coil 28 be mounted as shown in any of Figs. 6, 7, 8 and 9, that is, in an aperture of a vibrating element 26 so that the movement of the vibrating element will be symmetrical with respect to the coil and the coil is wound symmetrically about a magnetized core, the flux linking the core of the coil to the vibrating element will be constant and the number of turns out by the flux will be proportional to the displacement of the vibrating element. If the vibrating element is mounted as shown in Fig. l or 2 it will vibrate in practically pure harmonic motion, so that, with the use of any of the eXpedients of Figs. 6 to 9, the electromotive force generated in the coil will have practically a sine wave form. This wave may be amplified and a port-ion of the amplified energy used to drive the vibrating element as in Fig. 1. I

In Figs. 6, 7, 8 and 9 the core 27 may be a permanent magnet or may be polarized by means of a second coil 29 (F 7) wound thereon, through which a'current is passed.

A flux linking the magnetic core 27 to vibrating element 26 may be concentrated in a narrower space by narrowing the inner peripheral surface of the annular aperture in which the coil is mounted, as shown in Figs. 8 and 9. With th1s arrangement the coil 28 may be made narrower wlthout decreasing the electromotive force induced ber of turns may therefore be wound in the portion of the greatest flux density.

It is understood that a mechanical vibrating element may be mounted on a flexible mounting element as shown in Figs. 1 and 2 and may have a pick-up coil associated with it in the manner shown in Figs. 6, '7, 8 and 9, and also, in any instance where the shape of the wave induced in a pick-up coil warrants it, a compensating distortion may be applied thereto in the manner disclosed herein in connection with Figs. 3, 4 and 5.

lVhat is claimed is:

1. In combination, a mechanically vibratory element, a support therefor, and mounting means connecting said element and said support, said means comprising structure which is highly flexible as compared with said element, and means for deriving an elec tric wave from said element.

2. In a vibratory frequency standard organization, an element adapted to vibrate when mechanically stressed, means for converting the vibratory energy of said element into corresponding electrical energy, a utilization circuit, and electrical means between said converting means and said circuit ad apted to produce a distortion of the wave presented thereto complementary to the varia tion of the wave generated in said converting means from simple harmonic variation, whereby the resultant electrical wave represents substantially a simple harmonic variation. V

3. A vibrating element, a support therefor, means for deriving an electric wave therefrom and flexible means for dynamically isolating said element from said support.

a. A mechanical vibrating element, a space discharge element adapted to regeneratively pick up energy therefrom and deliver energy thereto, an energy utilizing circuit coupled with said element and means included in said circuit for istorting the wave delivered thereto compensatorily with respect to the distortion attendant on the production of the wave in said regeneratively related elements.

5. A mechanical vibrating element, a space discharge element associated therewith, means for impressing energy non-sinusoidally upon said space discharge element from said mechanical vibrating element, and space charge device, an means for introducing a complementary dissymmetry in said wave by the operation of said space discharge device.

7. A mechanical vibrating element, means for transforming the motion of said element into an electrical wave, a space discharge device associated therewith, and means for applyin said wave to a particular portion of the c aracteristic curve of said space discharge device as will tend to cause said device to distort the wave applied thereto in compensation of the distortion inherent in said transforming operation.

8. A constant frequency system comprising a mechanical vibrating element, a pick-up de vice electrically connected thereto adapted to translate mechanical vibrations into electrical oscillations, a utilization circuit, between said device and said circuit and means comprising a space discharge device for precludmg the introduction of harmonic frequencies into said circuit.

9. A vibrating element, a support therefor, means for dynamically isolating said element from said support, a space discharge device adapted to pick up distorted energy from said vibrating element, and means for applying compensating distortion to the wave received by said space discharge device from saidvibrating element.

10. A constant frequency system comprising a mechanical vibrating element, a supporting member thereof, means for dynamically isolating said element from said sup-- porting member, a circuit for deriving electrical energy from said element and means between said element and said circuit, for preventing the introduction of harmonic frequencies into said circuit.

11. In a vibratory frequency standard organization, an element adapted to vibrate when mechanically stressed, an opening in said element, a stationary generator coil in said opening, an energy utilization circuit connected thereto, and a magnetic circuit comprising said element and said coil.

12. In a vibrating frequency standard organization, an element adapted to vibrate when mechanically stressed, an opening in said element, a magnetic element within said opening, a coil mounted upon said magnetic element, and an energy utilization circuit connected to said coil.

13. In combination an element adapted to vibrate when mechanically stressed, an opening-in said element, an element of magnetic material within said opening, a coil wound upon said magnetic element, said opening being smallest in a plane midway between, and

CERTEFiCATE GE CURRECTIGN.

Patent No. 1,906,985. May 2, 1933 WARREN A! MARRiSG-Ne it is hereby certified hat error apgiesrs the ,erizated specification of the 4 first. column,

above numbered peters: requiring correction as ioiows: Fags: line 25, ciaim 8, strike out the words "and means" and insert the same before "between" in iine 24-; and time the said Letters iatent should be read with this lee record of the case in the correction therein that the same may conform to t Patent Office Signed and sealed this 7th day of Jamuary A. B. 3936.

Lesi ie Frazer (Seal) Acting Commissioner of Patents.

CERTZFIflATE 0F CQRRECTIGN.

Patent No 1,996,985. May 2, 1933 WARREN A, MARRESQ'NP at is hereby ceriitiesd that errar apgxears the gzrixated specificatisn a? th: abeve mum-harm patsm requiring care-mien as iailmvs: Fags first. eciumn, line 25, claim 8, strike out the wards "and means" and insert the same before "between" in Hue 24; and flat the saiii Lettars 33mm shouid be read with this correctisn lherein that the same may caniorm to ihe record of the case in the Patent Office Signed ml sealed this 7th day sf January, A. B. 1936.

Les! ie Frazer (Seal) Acting (Iammissioner of Patents.

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