US2260847A - Vibratory frequency standard - Google Patents

Description

Oct. 28, 1941. H, E WARREN 2,260,847

VIBRATORY FREQUENCY STANDARD Filedv May 27, 1938 3 Sheets-Sheet l Inventor Henry E.War-r`en,

oct. 28, 1941. H E WARREN VIBRATORY FREQUENCY STANDARD Filed May 27, 1958 3 Sheets-Sheet 2.

cf. 28, 1941. H E WARREN 2,269,847

VIBRATORY FREQUENCY STANDARD Filed May 27, 1938 3 Sheets-Sheet 5 AAAAA u ITM/er1 tor: Henry War-ren? by His torrwey.

Patented Oct. 28, 1941 VIBRATORY FREQUENCY STANDARD Henry E. Warren, Ashland, Mass., assignor to Warren Telechron Company, a corporation of Maine Application May 27, 1938, Serial No. 210,492

Claims.

My invention relates to vibratory frequency or time standard devices and particularly to such devices for use in controlling with great precision systems of clocks, power stations frequency, the movement of large telescopes, or for like uses.

In certain applications of frequency standard apparatus such as the control of the driving means of telescopes it is essential that the apparatus operate with the highest degree of precision. At the same time it is highly desirable that the apparatus be simple, easily mounted and adjusted, and free from complicated vacuum tube circuits.

It has been proposed heretofore to employ quartz crystal devices as frequency standards for the above and similar applications. Time or frequency standard apparatus of this character has, however, entailed the disadvantage that the primary frequency is of necessity comparatively high, being of the order, for example, of one hundred thousand cycles per second. To reduce this frequency to the relatively low frequency desired for telescope control andt similar uses requires a complicated system of vacuum tubes and circuits,

with very careful adjustment and constant supervision. Further, desired frequency changes in frequency standard devices incorporating the quartz crystal are not readily made.

Another frequency standard apparatus heretofore proposed but which employs a vibrating tuningfork, is also, like the quarts crystal apparatus, not readily capable of convenient'change of frequency at will. Furthermore, it has been of gravity in combination with elasticity to produce a vibrating system which is substantially free from frequency error due to variations in amplitude of vibration and variations in ambient temperature.

Another feature of my invention is the pro- Vision of novel means for maintaining amplitude of vibration approximately constant through a vacuum tube circuit.

A further feature of my invention is the provision of highly convenient and accurately operating means for changing the rate of vibration of the system from a remote point.

In carrying my invention into effect I employ an electrically driven, elastic tensioned element which is preferably a vibrating strip, string, wire or other suitably shaped member held under tension by a weight, or in some cases by a spring means. I have found that numerous difliculties stand in the way of obtaining accurate results by means of a frequency -standard instrument constructed in this manner. Among these dimculties are varying tension upon the vibrating element, disturbance due to the driving force, change in rate of vibration with changes in vibration amplitude, reaction from vibration of the supporting or mounting means for the vibrating element, reaction between the vibrations of the element simultaneously in different directions especially axially and transversely, very large temperature coefllcient of elasticity in many mafound, ordinarily, that the preparation and calibration of a high precision, vibrating tuning fork apparatus isa difficult and expensive operation, tuning forks in general being highly susceptible to frequency variations due to temperature and vibration amplitude changes;

It is, therefore, the primary object of my inventlon to provide a frequency standard apparatus which is characterized bythe extreme degree of precision required in the control of telescopes terials as Well as troublesome temperature coeicient of linear expansion, and effects due to air friction and ai-r motion upon the vibrating element. In accordance with my invention the above difficulties, and others, encountered in the provision of a frequency standard device employing an electrically driven elastic tensioned element such as a string, wire or strip under tension, are overcome.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. lyly invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawings wherein Fig. 1 is a representation, semidiagrammatic, of a frequency standard system in accordance with my invention ,comprising a frequency standard device, having a tensioned elastic vibrating element, connected to a vacuum tube circuit for actuating the tensioned element and for supplying power to a load device; Figs. 2 to 6 show curves, illustrating the invention, in which changes in vibration frequency of a vibrating ele- `ment are plotted against variations in amplitude of vibration; Fig. 'l illustrates diagrammatically another 'vacuum tube circuit suitable for use with my frequency standard device; and Figs. 8 and 9 illustrate modifications of the frequency standard device. .f

In Fig. 1 the numeral II) designates an elastic tensioned element which in the present embodiment of the invention comprises upper and lower lengths II and I2 of wire, strip, or other suitably shaped elements preferably formed of a material having a high negative temperature coefficient' of elasticity, and a central section I3 preferably formed of material, such, for example, as tempered steel or beryllium-copper a1- loy, having a high positive temperature coefcient of elasticity. By the term positive temperature coefficient of elasticity it is meant that materials characterized .by such coefficient become less stiff with increasing temperature, and by the term negative temperature coefficient of elasticity that the stiffness of the materials so characterized increases with increasing temperature. An example of a suitable material having a high negative temperature coefficient of elasticity is the nickel steel alloy known as Invar which contains approximately 36 per cent of nickel. This material belongs to a group of nickel steel alloys the characteristics of which are described in circular 58 of the Bureau of Standards, page 22.

The central section I3 is preferably wound in the form of an open spiral in order that the vibrating element I0 may be somewhat elastic in an axial direction. Mounted in the center of the central wire section I3 and transversely thereof, and preferably centrally of the vibrating element I0, is a small magnet I4, preferably permanent, which forms a part of the element I and which serves to couple the latter element I0 with a vacuum tube circuit I5 through a driving coil or winding I6 and a pickup coil or winding I1 within which coils the magnet I4 can vibrate freely in an axial direction. In the present embodiment gravity tension upon the vibrating element I0 is provided by means of a relatively heavy weight I8 rigidly connected to the lower wire section I2 of vibrating element I0.

The upper section II of vibrating element III is connected to a rigid support I9 adjustably connected to a heavy framework or support 2l, contributing in itself a high degree of stability to the device, which is mounted upon a relatively heavy base member 2I provided with leveling screws 22. The operating parts may be protected from the effects of variations in atmospheric pressure by' a bell jar 23 resting on'a suitable gasket 24 and having an exhaust connection 25 which provides means for obtaining any desired pressure inside the bell jar below atmospheric pressure.

For the purpose of making small adjustments in the rate of vibration of element III, movable weights 26 may be placed on the main weight I3. In order to compensate for changes in rate of vibration of element I0 due to changes in amplitude of vibration a small permanent magnet 21 provided with an adjusting screw 28 is preferably mounted in line with driving magnet I4. A very convenient means for adjustment of the rate of vibration of element Il) comprises a fine wire solenoid 29, connected to a direct current source (not shown) and mounted beneath the weight I8,

and a permanent magnet 3U connected to weight I8 and projecting into the solenoid. 'I'he energizing current for solenoid 2! and therefore the rate of vibration of element II) may be arranged to be adjusted from a remote point.

Instead of locating the beryllium copper or hardened steel portion I3 centrally of vibrating element I0 it is of advantage in certain cases to locate this portion at or toward the lower end of element I0 and entirely below the point of attachment of the driving magnet I4, and to extend downwardly the portion II, which is comparatively inelastic in the axial direction, so that the driving magnet may be mounted on this latter portion. In this arrangement the vertical position of the drawing magnet is not affected by change in tension of element III produced when the vibration frequency is changed by means of the magnet 2lil and solenoid 29. By this modification of element I0 it is possible to adjust the instrument over a wider range in frequency without producing a vertical interference between the oscillating magnet I4 and coils I3 and I1.

To prevent undesired slow oscillations of the weight I8 in any direction a damping means is provided which may comprise an oil reservoir 3I mounted below the solenoid 23 and a damping member within reservoir 3| including a cross shaped vane 32 fastened to a relatively large disk 33, the damping member being connected to the magnet 30.and therefore to weight Il.

The vacuum tube circuit or power unit Il preferably comprises a space discharge device or tube 34 having a grid or input circuit 35 which includes pickup coil or winding I1, and an anode or output power circuit 36 which includes driving coil or winding I6. Tube 34 is preferably of the heater type and of high amplification factor and sharp cut-off, such, for example, as a tube of type 6F5. An adjustable negative grid bias may be provided .by a potentiometer 31 connected between the cathode 38 and the negative terminal of cathode heating source or battery 39. Voltage, which may be relatively low, for the anode 4l of tube 34 is provided from a current source or battery 4I through a resistor 42.

An amplifier 43 for the voltage generated by the frequency standard apparatus is preferably connected to the output of tube 34. for example through a resistance coupling comprising a usual coupling resistor and a condenser 44 which may be connected, as illustrated, to the outer terminal of resistor 42 ordirectly to anode" of the tube 34. The amplifier 43 may be connected as a driver for a power amplifier (not shown) through a transformer 45 or other suitable connection.

In operation of the frequency standard -system illustrated in Fig. 1, vibration of the magnet I4, which is supported by the wire or strip tensioned by the Weight I8, with reference to the pickup coil I1 generates a potential which is impressed upon the grid of tube 34. The potential impressed on the grid has substantially a sinusoidal wave form due to the harmonic vibration of the magnet I4 with reference to coil I1, and since the coil I1 is preferably wound with a large number of turns this potential may be of relatively high yvalue, of the order, for example, of 800 millivolts. Amplified energy from the output circuit of tube 34 is then fed back to driving coil or winding I6, an end of which encloses an end of the magnet I4, at a rate sumcient to sustain the oscillations of the element III, the points of attachment of element I0 to support I3 and to the tensioning weight I8 constituting the nodal points of the oscillations.

When the element Ill vibrates through a relatively small amplitude the plate current through driving coil I6 and resistor 42 is also substantially sinusoidal. However, as the amplitude of vibration of element ID increases, and the sinusoidal potential impressed on the grid of tube 34 correspondingly increases, the peak negative potential finally, at each oscillation, goes beyond the cut-off point. There is then a tendency to check further increase of energy fed back to maintain the oscillation of element I Il on the negative half of the current wave. Although some increase of the fed back energy may still occur on the positive half wave' of the grid potential, this latter increase is limited by the value of anode current resistor 42. Consequently the type of tube illustrated ,in Fig. l tends definitely to maintain a substantially constant amplitude of the vibrating element I0.

oscillations of the desired constant frequency, produced Vin the output circuit of tube 34 and amplified in amplifier 43, are preferably further amplified in a power amplifier (not shown) which may be arranged to supply a relatively large amount of energy of the desired constant frequency to a load or power circuit associated, for example, with a time indicating device (not shown), or with mechanism (not shown) for controlling the motion of a large telescope or other device requiring similar close control of motion. In certain applications, however, the power amplifier and the output transformer 45 connecting amplifier 43 thereto may be dispensed with, since it is possible to obtain a considerable amount of output energy from amplifier 43, sufficient, in fact, to operate, directly, a very small synchronous motor.

The weight (I8) required to obtain a definite desired frequency of vibration of element 10 may be determined approximately by the formula r. K l

W here f=frequency in cycles per second W=main weight (I8) w--weight of magnet I4 Z=length of vibrating element I0 K=a constant This formula shows that the rate of vibration varies inversely with the length of the vibrating element'or Wire, directly with the square root of the main weight (I8) and inversely with the square root of the weight of the driving magnet The vibrating element I0 is susceptible also to vibration in an axial direction and the frequency of such vibration is determined approximately by the formula C f w/LW where C is a constant and l and W represent respectively, as before, length of the vibrating element I0 and the main weight (I 8). In the latter formula the weight of the magnet I4 has been ignored.

It is possible, by varying the proportions of the frequency standard device, to bring about a condition wherein the vertical frequency of vibration of the vibrating element II) is4 double its transverse frequency. Under these latter conditions no useful vibration can be maintained in the device since the effect of the vertical vibration is to damp out, almost instantly, the transverse vibration. In order for the transverse Vibration to be maintained efficiently no condition of resonance should exist between the two systems of vibration. It is desirable that the proportions of the device be so chosen as to avoid troublesome harmonics of the axial vibration of the vibrating element which might interfer with the transverse vibration. Therefore, it is desirable so to form the vibrating wire or strip and so to determine the weights I8 and I4 as to avoid resonance between these two forms of vibration.

If, for the vibrating element I0, a single wire or strip be employed to support the weight I8 and the magnet I4, without the provision of any extra elasticity in the vibrating element in the vertical direction, such as provided in Fig. 1

`by the coiled section I3, desired transverse vibration may very easily be maintained provided the device is so proportioned as to avoid resonance between axial and transverse vibration. However, while, with such construction of the device, the frequency of vibration is substantially constant for a given amplitude of vibration,-the frequency varies to an objectionable extent with variations in amplitude of vibration, as illustrated by the curve of Fig. 2, plotted for a device of the latter construction, which shows that with such construction the rate of vibration increases rapidly with increase in amplitude of vibration.

However, if an elastic connection be introduced between the main weight and the vibrating wire, either in a portion of the wire itself, as illustrated for example by the central section I3 of element I0, or at one end, for example the lower end, of the vibrating wire, the varying of the rate of vibration with respect to' amplitude of vibration may be greatly modified. Thus the curve of Fig. 3 shows a condition which may be obtained by proper proportioning of the elasticity and length of the elements constituting or associated with the vibrating element. The latter curve shows that over a small range the rate of Vibration Ibecomes actually less with increasing amplitude of vibration, and that the curve then reverses its direction and the rate of vibration gradually increases with increasing amplitude of vibration. For a very considerable portion of the working range the amplitude-rate curve is substantially horizontal, indicating that, over this portion, variations in amplitude of vibration produce a negligible effect upon the rate of vibra-- tion. f

Compensation for changes in rate of vibration 1 due to changes in amplitude of vibration may be accomplished also by means of the permanent magnet 2'I which is mounted in line with the driving magnet I4 and provided with an adjusting screw 28. 'I'he two magnets are so arranged that their adjacent poles are of opposite sign, and the magnets, therefore, tendto attract each other. The attraction varies inversely as the square of the distance between themagnets, and this controllable force due to the action i compensation, over a small amplitude range, for changes in rate of vibration tending to occur due to change in amplitude. It is also possible to eilect small changes in rate of vibration by adjustment of the screw28.

In Fig. 4 the curve shows the relation between rate and amplitude of vibration when the air gap between magnets I4 and 2'1 is comparatively large. Curve 4 shows that in this case the rate of vibration increases with increasing amplitude, the magnet 21 having little effect. Fig. 5 shows, on the other hand, the rate-amplitude relation when the air gap between magnets I4 and 21 is very small. In Fig. 5, the rate of vibration decreases relatively rapidly with increasing amplitude. Fig. 6 shows the rate-amplitude relation when the air gap between magnets I4 and 21 is such that the rate of vibration first increases with increasing amplitude of vibration and thereafter decreases. In Fig. 6 a portion of the curve is substantially horizontal, showing that, for the latter air gap setting, over a limited range the amplitude variations produce negligible variations in rate of vibration.

In the making of small adjustments in the rate of vibration of the element I by means of the movable weights 26, the value of these weights for a given number of seconds or time period per day may be readily and accurately calculated. 'I'he frequency standard device, employing the gravity tensioned vibrating element as illustrated in Fig. 1 may be corrected easily, by the use of auxiliary weights 26, after comparison with the daily time signals.

In adjusting the rate of vibration of the vibrating element I0 by means of the solenoid 28 and magnet 30 mounted beneath the main weight I8, when no current is flowing in solenoid 29 the rate is determined by gravity, but by passing a measured current through the solenoid the gravity eifect may be increased or diminished to any desired extent, for the purpose, for example, of changing the rate of motion of a telescope following a star or planet.

With regard to the eilect of temperature in connection with my frequency standard device, I have found that if the wire or strip of vibrating element I0 is formed of a single material, this element will be more or less susceptible to temperature changes. The latter effect is not so much due to the change in length of the.single wire or strp with temperature, which may be corrected easily by using'material having a low or substantially zero temperature coemcient of expansion, as to the fact that the elasticity of the material plays an important part in determining the rate of vibration. This is duejin part at least, to the necessary flexing of element I0 near its points of support and also in the central portion when vibration occurs. Even amaterial having, together with a desirably low, or zero, temperature coeilicient of expansion, a low temperature coeflicient of elasticity exhibits varia tions in the rate of vibration with temperature if employed alone as material for the wire or strip of vibrating element I0.

However, by combining as hereinabove explained, two materials, in vibrating element III, which behave differently under temperature variations, such as hardened steel or beryllium-copper alloy and a material such as Invar having a high negative temperature coefficient of elasticity, it is possible to obtain very accurate compensation for the temperature changes which take place in the two materials. This compensation is readily accomplished for the reason that the temperature coeillcient of elasticity of steel or beryllium copper alloy is opposite in sign to the temperature coeiilcient of elasticity'` of the other material. With increasing temperature hardened steel and the above alloy become less stiiI while with increasing temperature the other material becomes more stiif. I have found that it is possible so to choose the proportions of this other material which is under elastic stress, and the proportions of the steel or alloy which is also under elastic stress that the effect of temperature upon the steel or alloy is exactly cancelled by the effect of temperature upon the other material in the opposite direction. With regard to temperature eifect in altering the length of the wire or strip or similar elements comprised in vibrating element I0, a small residual of this latter effect remaining can be eliminated by a slight amount of over-compensation for the elasticity effect.

It is preferable in the arrangement of the vibrating element I0 as illustrated in Fig. 1 that the vibrating parts which are under elastic stress have a small and approximately equal cross section so that response of element I0 to temperature changes may be very prompt and difficulties duee to lag in temperature change may be obvia d.

In Fig. 1 the vibrating element III is shown as comprising an elongated hardened steel spring Il and two wires, I I and I2, of material, which is usually Invar, of high negative temperature coefiicient of elasticity.' However, not only may the wire be a strip or other suitable shape and the elastic portion of element I0 b e located at either end thereof, as explained hereinbefore, but other dissimilar materials may be used than the two above-described. Further, instead of driving the wire, strip or other similar element by means of a magnet mounted on the vibrating wire or element and cooperating with the fixed coils I6 and I1, the driving may be accomplished by mounting the coils I6 and I'I on the vibrating wire or element and providing one or more magnets cooperating therewith. It is, further, possible to utilize the vibrating wire or element itself as an electrical conductor which, when suitably arranged in a strong magnetic field, is set in vibration by the action of a suitable electronic device.

In Fig. I I have illustrated a vacuum tube circuit 46 for driving the vibrating element I l of Fig. 1 wherein an automatic volume control circuit is utilized to control the amplitude of vibration of the latter element I0. The circuit 46 comprises a space discharge device or tube 41 having an input circuit 48 including a pickup winding 49, corresponding to and adapted to replace the pick up winding I6 of Fig. l, and an output circuit 50 including a driving winding 5I, corre-v sponding to and adapted to replace the driving winding I1 of Fig. 1. The output circuit of tube 41 is connected to an ampliiier 52 in a manner similar to the connection of tube 34 to tube 43 in Fig. 1. The output circuit of tube 52 is preferably connected through a transformer 53, having a secondary 54, to a push-pull power amplifier 55 the output of which may be connected to a utilization circuit (not shown).

To provide a negative bias on the grid of tube 41 varying in accordance with the output o1' the tube, a portion of the output from transformer 53 is rectified in tube 41 at the auxiliary electrodes 5l and 51 connected to the terminals oi' secondary 54. The current thus rectiiied flows from the cathode of tube 41 through resistors B and 58 in series, back to the midpoint 60 of secondary 54. Resistor 58 is included in the gridcathode circuit of tube 41. The potential drop through resistor 58' provides a predetermined negative bias for tube 41 in normal operation. If, however, the amplitude of vibration of the vibrating element, such as element I0 of Fig. 1, with which windings 49 and 5I are assumed to be associated, tends to change during operation, the rectified current through resistor 58 tends -to change correspondingly, the connections being such ,that the grid bias in tube 41 due tothe potential drop in resistor 58 tends to change in a direction to cause the output of tube 41 to compensate for the change in amplitude of vibration of the vibrating element.

Fig. 8 illustrates a modication similar in general in construction and operation to the embodiment of Fig. 1 but wherein the elasticity of the vibrating element comprising vertical sections 6l of material such as Invar having a high negative temperature coefiicient of elasticity is concentrated at one end by the provision of a bent strip or similar resilient member 62 of hardened steel or beryllium-copper alloy mounted transversely of the frequency standard device on a support 63 at the lower end of the vibrating element. Further, in the modification illustrated in Fig. 8, for the tensioning force supplied by the main weight I8 of Fig. 1 is substituted the force exerted by spring tension of the resilient member 62, this tension being adjustably controlled by a screw 64, suitably mounted on the supporting frame 65, provided with an adjustable nut 66 and connected to the support 63 upon which' resilient member 62 is mounted. Substantial uniformity of the tensioning force is assured by the elasticity of the transverse spring member 62.

Fig. 9 illustrates a modification similar to the embodiment of Fig. 1 but more particularly designed for portable use, or for mounting on shipboard or in other locations where gravity means such as the main weight I8 of Fig. 1 could not well be used to provide a definite tensioning force acting upon the vibrating element, designated by the numeral 61. Element 61 is preferably identical in all respects with vibrating element I0 illustrated and described in connection with the embodiment illustrated in Fig. 1. Instead of applying tensioning pressure to the vibrating element 61 by means -of a weight as in Fig. 1, in the modification illustrated in Fig. 9 this pressure is applied in a manner somewhat similar to the application of tension to the vibrating element 6I of Fig. 8, by a screw 68, having an adjustable nut 69, connected directly to the lower end of vibrating element 61. Substantial uniformity of the tensioningy force upon element 61 is assured by the elasticity of its coiled spring portion 18. The elimination of temperature effects may be obtained by the proper proportioning of the elements constituting vibrating element 51, with reference to the effect of temperature upon the supporting framework 1|.

My invention has been described herein in particular embodiments for purposes of illustration.

It is to be understood, however, that the inven-` tion is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a frequency standard apparatus comprising a vibrator device, a vertical flexible vibrator element for said vibrator device having a. substantial degree of elasticity lengthwise, a rigid support, means to connect said element at its upper end to said support, a weight to tension said element connected thereto at the lower end thereof, and electromagnetic means to maintain said element in vibration, said electromagnetic means being operative at such point of said element that the point of attachment of said element to said weight constitutes a nodal point of the vibration of said element.

2. In a frequency standard apparatus comprising a vibrator device, a vertical ilexible vibrator element for said device composed of two different materials having respectively temperature coeiicients of elasticity of opposite sign, and a tensioning weight connected to said element, the point of attachment of said weight to said element constituting a nodal point of the vibration thereof.

3. InV a time measuring instrument comprising a vibrator device and a space discharge device circuit to drive said device coupled electrically thereto, a vibrating string for said vibrator device composed of at least two sections having differing degrees of elasticity, and adjustable means to tension said string.

4. In a time measuring instrument comprising a vibrator device and a space discharge device circuit to drive said device coupled electrically thereto, a vibrating string for said vibrator device composed of two sections of differing degrees of elasticity and having respectively temperature eoeilicients of elasticity of opposite sign, and adjustable means to tension said string.

5. In a time measuring instrument'comprising a vibrator device and a space discharge device circuit to drive said device coupled electrically thereto, a vibrating element for said vibrator device comprising a member -slightly elastic lengthwise and a member having a substantial degree of elasticity lengthwise, and adjustable means to tension said vibrating element.

6. In a. time measuring instrument comprising a vibrator device and a space discharge device circuit to drive said device coupled electrically thereto, a vibrating element for said vibrator device comprising a member slightly elastic lengthwise and a member having a substantial degree of elasticity lengthwise, said members having respectively temperature coefficients of elasticity of opposite sign, and adjustable means to tension said vibrating element.

'7. In a time measuring instrument comprising a vibrator device and a space discharge device circuit to drive said device coupled electrically thereto, a vibrating string for said vibrator device having a substantial degree of elasticity in the axial direction thereof, and adjustable means f circuit to drive said device coupled electrically 9. In a frequency generator apparatus com-v prising a vibrator device, a power circuit, and means to couple said vibrator device to sa1d power circuit, a vibrating string for said vibrator f device having a. substantial degreefof elasticity lengthwise, means to tension elastically said string, and electromagnetic means to drive said string.`

10. In a frequency generator apparatus comprising a vibrator device, a power circuit, and means to couple said vibrator device to said power circuit, a vibrating string for said vibrator device composed of at least two elements having temperature coefficients of elasticity of opposite sign, means to tension elastically said string, and electromagnetic means to drive said string.

11. In a frequency generator apparatusoomprising a vibrator device, a utilization circuit, and electrical means to drive said vibrator device and to couple said vibrator device to said utilization circuit, a vibrating string for said vibrator device composed of a plurality of elements in tandem, one of said elements having a temperature coefficient of elasticity opposite in sign to that of the temperature coefficient of elasticity of the remainder of said elements, and adjustable means to tension said string.

12. In a frequency standard apparatus, a vibratory element comprising a section composed of material having a negative temperature coeflicient of elasticity, and a section composed of material having a positive temperature coeflicient of elasticity.

13. In a frequency standard apparatus, a vibratory element comprising a plurality of sections, one of said sections being composed of material having a temperature coefficient of elasticity opposite in sign to that of the temperature coefficient of elasticity of the material of another of said sections, one of said sections being of such form as to provide a substantial degree of elasticity in the axial direction of said element, and means operatively associated with said element to produce a tensioning stress therein in the axial direction thereof.

14. In a frequency standard apparatus, a vi- .bratory element comprising a plurality of sections, one of said sections being composed of material having a temperature coemcient of elasticity opposite in sign to that of the temperature coefficient of elasticity of the material of another of said sections, one of said sections being of such form as to provide a substantial degree of elasticity in the axial direction in said element, and a weight operatively associated with said element and so arranged as to produce a tensioning stress in said element in the axial direction thereof.

15. In a frequency standard apparatus, a vibratory element comprising a section composed of material having a negative temperature coeflicient of elasticity and a section composed of material having a positive temperature coefficient of elasticity, one of said sections being of such form as to provide a substantial degree of elasticity in the axial direction of said element, a supporting means for said element, and means mounted in said supporting means'and connected to said vibratory element to produce a tensioning stress therein.

16. In a frequency standard apparatus, a vibratory element comprising a section composed i of material having a negative temperature coeicient of elasticity and a section composed ofv material having a positive temperature coeicient of elasticity, said last-named section being connected at a point intermediate its ends to said first-named section and transversely thereof, a

supportingmeans for said element, and means mounted in said supporting means and connected to said second-named section to flex said second 75 18. The combination with a frequency standard f apparatus comprising a vibratory element, and

means to produce a tension in said element axially thereof, of means to adjust the rate of vibration of said element including a solenoid, a source of current for said solenoid, and a magnet connected to said vibratory element and operatively associated with said solenoid.

19. 'I'he combination with a frequency standard apparatus comprising a vibratory element, and means to produce a tension in said element axially thereof, of means to adjust said tension in said element and thereby to adjust the rate of vibration thereof, said last-named means including a solenoid and a source of current therefor, and a magnet connected to said vibratory element and operatively associated with said solenoid.

20. 'I'he combination of a frequency standard apparatus comprising a vibratory element, means to produce a tension in said element axially thereof, and means for adjusting the rate of vibration of said element from a remote point, said last named means including a solenoid, a magnet connected to said vibratory element and operatively associated with said solenoid, and a source of current for energizing said solenoid adapted to be controlled from said remote point.

21. A frequency standard apparatus comprising a vibratory element having a plurality of sections, one of said sections being composed of material having a temperature coefiicient of elasticity opposite in sign to that of the temperature coefficient of elasticity of the material of another of said sections, a weight connected to said element to produce a tensioning stress therein, means to actuate said vibratory element including a magnet and two windings in operative relation therewith, and an auxiliary means to control the relation between amplitude of vibration of said vibratory elementand the rate of vibration thereof said last-named means including a magnet adjustably mounted adjacent to said first named magnet.

22. A frequency standard apparatus comprising a vibratory element having a plurality of sections, one of said sections being composed of material having a temperature coefficient of elasticity opposite in sign to that of the temperature coelcient of elasticity of the material of another of said sections, a weight connected to said element 4toproduce a tensioning stress therein, means to actuate said vibratory element including a magnet and two windings in operative relationtherewith, an auxiliary means to control the relation between amplitude of vibration of said vibratory element and the rate of vibration thereof, said last-named means includving a magnet adjustably mounted adjacent to said first named magnet, and an auxiliary means to alter the tensioning stress in said vibratory element thereby to control the rate of vibration thereof.

23. A frequency standard apparatus comprising a vibratory element, a weight connected to said element to produce a tensioning stress therein, means to actuate said vibratory element including a magnet and two windings operatively associated therewith, an auxiliary means to control the relation between amplitude of vibration of said vibratory element and the rate of vibration thereof, and auxiliary means for adjusting the amount of tension in said vibratory element.

24. A frequency standard apparatus comprising a relatively long vibratory element of relatively small cross sectional area, means operatively associated with said element to produce a tensioning stress therein axially thereof, and means to actuate said element including a magnet connected thereto transversely thereof and two coils 15 1o of, and means to actuate said element including a magnet connected thereto and a pickup coil and a driving coil operatively associated with said magnet at opposite ends thereof.

HENRY E, WARREN.k

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