US2346984A - Rate control for tuning fork oscillators - Google Patents

Description

April 18,1944. M. s. mama, JR 2,3 6, 8

RATE CONTRCIL FOR IEQRK OSCILLATOR-5 Fxiled Aug. 25,, 1,942

I FORK AMPLIFIER FORK AMPLIFIER Fig.5.

DECREASE INCREASE RATE RATE Fig.2.

| I ER 8 44 i P6. E9 Inventor:

Milton S. Mead J11,

y His Attorney.

SECONDS PER-DAY Patented Apr. 18, 1944 RATE CONTROL FOR TUNING FORK OSCILLATORS Milton S. Mead, Jr., Hempstead, N. Y., assignmto General Electric Company, a corporation of New York Application August 25, 1942, Serial N0. 456,001

'7 Claims.

My invention relates to oscillation generators, and more particularly to oscillation generators employing an electron discharge control device and including a frequency determining system of the mechanically vibratory type. It is an object of my invention to provide a control for such an oscillator which allows a wide range of adjustment of the rate of mechanical vibration of the frequency determining system.

In applications where it is necessary to maintain the output frequency of an oscillator substantially constant over long periods of time, as in clock supervisory systems, for example, oscillators employing a mechanically vibratory element, for example a tuning fork, have been found particularly suitable. Such oscillators usually include drive and pick-up coils associated with the tuning fork, which coils are coupled respectively to the output and input circuits of an electron discharge amplifier and are so arranged that vibration of the element controls the amplifier to produce sustained oscillations in the output circuit thereof.

It is an object of my invention to provide in an oscillation generator of the above described type means for controlling the frequency of vibration of the vibrating element which, while allowing a wide range of adjustment of the rate of vibration, maintains a constant amplitude of vibration of the vibrating element and consequently constant output voltage from the electron discharge amplifier.

A further object of my invention is to provide means for varying the frequency of vibration of a vibratory element by shifting the phase angle between the current in the driving coil and the vibrations of the element in such a manner that the change in frequency varies linearly with the position of a manual control member.

Another object of my invention is to provide a tuning fork oscillator having an adjustable rate of vibration which can be easily produced in large quantities and which includes means for readily adjusting the range of rate control for such production units.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in

- which Fig. 1 illustrates one embodiment of my in vention; Fig. 2 shows vectorially certain voltage relationships pertaining thereto; Fig. 3 shows an the discharge device. device 3 is similar in all respects to device I, with the exception that the single diode elecexample of the scale possible in the rate control device; and Figs. 4 and 5 illustrate schematically modifications of my improved rate control.

Referring to Fig. 1 of thedrawing, I have shown my improved oscillation generator as comprising an amplifier, including an electron discharge device I, which is controlled by a vibratory element 2 to generate electrical oscillations having a frequency determined by the frequency of vibration of the element 2. The vibratory element 2 is shown as a tuning fork, although it will be understood that other forms of mechanical vibratory elements may be employed Without modification of the circuit illustrated. The output of the device I is impressed of the single-diode pentode type and includes an anode 5, a cathode 6, control electrodes '1, 8 and 9 and a diode electrode I0, control electrode 9 being directly connected to the cathode ,6 and functioning as the usual suppresser grid to prevent secondary electron emission within The electron discharge trode is omitted.

The input circuit to the amplifier I includes asecondary ll of a coupling transformer I2 having its primary I3 connected to a pick-up coil I4 wound on the field structure of the tuning fork 2. For a purpose to be explained more fully later, the input circuit is connected across a phase shifting circuit, comprising resistance I5 and capacitor I6, the voltage across the capaci- -tor I6 being impressed between the control electrode 1 and the cathode B, of the discharge device I through an alternating current, by-pass condenser II.

The output circuit of the amplifier I includes the primary Winding I8 of a coupling transformer having its secondary winding I9 connected through a rate control .network 20, the

nature and function of which will be described in detail later, to excite a fork drive coil 2|. The

.winding I8 is connected between the anode 5 and cathode 6 of the device I in series with a source of high voltagedirect current potential 22 and a resistance 23. .A condenser 24 is connected in shunt with the winding I8 and functions to tune the inductance of the winding to form an oscillatory circuit 25 having a resonant frequency equal to the normal operating frequency which the apparatus is designed to produce.

The potential developed across the terminal of the oscillatory circuit 25 is impressed upon a resistance 25 connected to the oscillatory circuit by a pair of alternating current by-pass condensers 2'! and 28 included in the input circuit of device 3. Resistance 26 is connected between the control electrode and cathode of the discharge device 3 through a by-pass condenser A resistance 38, connected at one end to the negative side of the voltage source 22, serves to bias the control electrode ofv the device 3 negative with respect to the cathode thereof.

Th output circuit of the electron discharge device 3 includes the leads 4 connected respectively to the anode and cathode of the device electrode of device 3 through the voltage droping resistor 33. This resistor serves to-maintain the screen electrode at a positive potential slightly lower than the positive potential of the anode of device 3. In similar manner a biasing potential is impressed on screen electrode 8 of device 1 through thecircuit lead' which includes a voltage dropping resistor 34.

The vibratory frequency determining unit for controlling -the amplifier system described above includes the tuning fork 2 and a field structure comprising the core members 35, 36, upon which the drive and pick-up coils respectively are wound, and the permanent magnet member 31. Since this structure forms no part of my present invention, it will not be described in detail; instead, a description of this structure may be found in my UnitedStates Letters Patent No. 2,147,492, granted February 14, 1939, and assigned to the same assignee-as the present invention. The intensity of the unidirectional flux flowing between members 35 and 35, and in turn the negative compliance or stiffness of the tines of fork .2 may be adjusted by means of winding 38 on member 31 which is connected in series with thebattery 39 and the switch.

As has been previously-noted herein, my present invention is primarily concerned with the problem of providing means by which the rate of mechanical vibration of thetines of fork 2 may be varied over a wide range. For this purpose the rate control network 20 is provided across the secondary winding l9 supplying the fork drive coilil. This network comprises capacitor 4| and resistance 42 connected in series across winding l9 and having a common point 43 to which is attached one terminal of the drive coil 2| A fixed resistance 44 connected in shunt with the above mentioned'series circuit is provided with a variable point 45 to which theother terminal of drive coil 2| is connected through secondary winding of transformer 41, theprimary winding 48 of transformer 41 being connected in series withpick-up coil l4 and the primary winding l3 of transformer I2.

Operation of the above described oscillation generator may be initiated by impressing a current impulse on the drive coil 2|. Such an impulse changes the path of the flux, flowing betines of fork 2 by attracting or repelling these tines in accordance with the polarity and magnitude of said current impulse. Such movement of the tines of fork 2 alters the magnetic flux linking pick-up coil l4, generating in the pick-up coil an electromotive force which is a function of the current flowing in drive coil 2|. This electromotive force is impressed on the control electrode 1 of amplifier I through the coupling transformer l2 and phase shifting network l5, l6, where a phase shift of 90 is obtained, and

. causes an impulse of energy to flow in the output circuit of device i. A portion of this impulse of energy developed in the output circuit is delivered through the secondary winding I9 to the rate control circuit 23. When the variable contact 45 is adjusted to the mid point on the resistor 44, rate control network 29 produces a phase shift equal and opposite to that obtained in the phase shifting network l5 and I5. Under such conditions a current impulse flows in drive coil 2| in a direction opposite to the current flow of the initial current impulse. This produces an opposite movement of the tines of fork 2 causing a second voltage impulse to be generated in pick-up coil l4 having a sign opposite to that caused by the first movement of the tines. This second impulse of voltage exerts a controlling effect on the device I such that the instantaneous current flowing in the output circuit thereof is reversed in direction for the duration of the impulse. The interaction of fork vibration and amplifier ultimately reaches a condition of equilibrium in which the fork is vibrated at a substantially constant frequency determined by the amplitude of the alternating current in the drive coil 2|, the intensity of the unidirectional flux between members 35 and 36 and the natural period of vibration of the fork.

By adjustment of the position of variable contact 45, the phase between the voltage applied across the terminals of drive coil 2| and the vibrations of the fork may be altered so that the driving force exerted by the drive coil either leads or lags the fork vibrations. When the driving current is in phase with the vibrations of the fork, and hence with the pick-up voltage, the fork operates at its natural frequency. If the driving current is made to lag behind the vibrations of the fork, it reduces this frequency to a value below the natural frequency. On the other hand, if the driving current leads the vibrations of the fork, the rate of vibration is increased.

The manner in which my control acts to ine crease or decrease the rate of vibration of the ,element 2 may be explained by reference to Fig. 2.

In Fig. 2 if the vector E represents the voltage across the terminals of the winding |9, voltages across resistance 42 and capacitor4| are shown respectively by vectors ER andEc. The current flowing through the series circuit of resistor 42 and capacitor 4| is shown bythe vector I. It is, of course, apparent that the vo1tage:E represents likewise the voltage existing across resistance 44. The vector Eb, therefore, represents the voltage applied across the drive coil 2| when the variable point 45 is adjusted to the mid position of resistance 4.4. Under such conditions, the circuit constants are adjusted so that the driving-force producedby the current flowing :in drive-coil 2| is in phase with the vibrationsof the fork. When the variable contact 45 is moved to some other position, .such as 45", the voltage applied=across theterminals 43, '45 of the drive coil circuit is tween the core, members '35 and 36 through 1-,he

represented by the'vector-E'D. Under these conditions the driving force lags the vibrations of the fork and reduces the output frequency of the system. The increased driving current secured when the control is off center position is automatically the amount required to furnish the increased driving force necessary to cause the fork to vibrate with the same amplitude at the new phase angle, which the fork must assume to match the phase shift through the amplifier.

As a result of this constant amplitud of vibra-' tion of the fork, the magnitude of the voltage generated in the pick-up coil I4 remains constant, resulting in a constant output voltage for the amplifiers I and 3. The out-of-phase component of the voltage E'n is effective to reduce or increase the frequency of the voltage appearing in the pick-up coil I4 with resultant variation in the frequency of a voltage across the terminals 44. Moreover, the vector diagram of Fig. 2 shows that the magnitude of this out-ofphase component of the voltage of E'p varies linearly with the adjustment of the contact 45 from the mid point of resistance 44.

Fig. 3 shows an example of the scale which may be used for the rate control when a well known type of potentiometer is used for the variable resistance 44. The actual value of increase or decrease in frequency is a function of the decrement of fork 2. If the fork has a very low decrement, it can vibrate with a large phase angle between the driving force and the fork velocity without experiencing but a slight change in frequency.

In order to neutralize the effect of voltages generated in the drive and pick-up coils due to the inductive coupling between these two coils, the coils are both loosely coupled and transformer 41 is provided, with its windings 46 and 48 connected respectively in the drive and pick-up circuits, to introduce in either of the two circuits a potential which is opposite in phase to the potential generated by the coupling of the coil windings and equal in magnitude to the voltage produced by such coupling.

Also, in order to maintain as nearly constant as possible the magnitude of the output current of the amplifier I, a circuit is provided for supplying a biasing potential to control electrode 1 ofdevice I which varies in accordance with the intensity of the output current fiowing between the anode 5 and the cathode 6. This automatic biasing circuit, comprising the diode formed by the element Ill and the cathode 6, coupling capacitor 49 and resistances 50 and 5|, functions to maintain substantially constant the anode current of device I by utilizing the unidirectional current flowing between element In and cathode 6, resulting from the alternating potential impressed thereacross through capacitor 49, to develop a unidirectional potential across resistor 50. This unidirectional potential is impressed on control electrode 1 through resistance 5i and winding II of transformer I2 and varies the biasing potential impressed on the control electrode 1 with, and in proportion to, the magnitude of the current flowing in the anode circuit of the amplifier.

In order to provide a constant potential for the screen electrode 8 of device I, an electric discharge device 52 is connected between the electrode 8 and the cathode 6. Since the screen electrode 8 is connected to the source of potential 22 through resistance 34, the device 52, which may comprise an ordinary glow discharge tube having a pair of spaced electrodes positioned within a container filled with an ionizable medium, such as neon, acts in a well known manner to vary the current flow in direct proportion with variations of the potential source 22, thus maintaining the potential of the grid 8 with respect to the cathode 6 at a constant value. In this manner the magnitude of the current supplied to the drive coil 2| is maintained substantially constant. Switch 53 is provided in order to supply a high voltage impulse for starting tube 52.

In the rate control for a tuning fork-oscillator illustrated in Fig. 1, a wide range of adjustment may be secured by varying the position of contactv 45 between the extreme limits of resistor 44, a phase shift of in operation being secured with constant fork amplitude.

In Fig. 4 is shown one modification of the control illustrated in Fig. 1. In this figure, parts corresponding to Fig. 1 are identified by corresponding reference characters. Inthis modification fixed resistors 54 and 55, of equal ohmic value, are connected in series with resistor 44, decreasing the rangeof rate variation.

In the modification illustrated in Fig. 5, I have shown how my rate control may be connected between the pick-up coil and the input to the fork amplifier when operating conditions make sucha change desirable.

It will thus be seen that my improved oscillation generator provides means whereby a wide range of adjustment of the rate of vibration of a mechanical vibratory element may be secured while the output voltage from the vibration amplifier is held constant for all settings of the rate control. Moreover, my control is characterized by the linear relationship between the change in frequency and the change in the setting of a potentimeter.

While I have shown particular embodiments of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made, and I contemplate by the appended claims 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 combination, a vibratory element, means associated therewith for generating a voltage having an intensity determined by the amplitude of vibration of said element anda frequency determined by the frequency of vibration of said element, an output circuit connected to said! voltage generating means, means including a drive coil coupled to said output circuit for supplying a driving force to said element, and means for varying the phase between said driving force and said element, said phase varying means comprising a resistance and capacitor connected in series across said output circuit, a second resistance connected in shunt therewith, and means for connecting said drive coil between the common point of said resistance and capacitor and a variable point on said second resistance.

2. In combination, an oscillation generator comprising a vibratory element, an electron discharge device having an anode, a cathode, and a control electrode, input and output circuits connected to said device, means including a drive coil coupled to said output circuit for supplying a driving force to vibrate said element, means including a pick-up coil for controlling the frequency of current in said output circuit in accordance with the frequency of vibration of said element, and means for varying the frequency of vibration of said element, said last-named means comprising a phase-shifting circuit connected across said output circuit, and means for adjustably connecting said drive coil across said phaseshifting circuit, whereby the phase angle between said driving force and said element is varied.

3. In combination, an oscillation generator comprising a vibratoryelement, an electron discharge device having an anode, a cathode, and a control electrode, input and output circuits connected to said device, means including a drive coil coupled to said output circuit for supplying a driving force to vibrate said element, means including a pick-up coil for controlling the frequency of current in said output circuit in accordance with the frequency of vibration of said element, and means for varying the frequency of vibration of said element, said last-named means comprising a capacitor and a first resistance connected in series across said output circuit, said capacitor and first resistance having a common point, a second resistance connected in shunt to said output circuit, and means for connecting said drive coil between said common point and a variable point on said second resistance, whereby the phase angle between said driving force and said element may be varied.

4. In combination, a vibratory element, means associated therewith for generating a voltage having an intensity determined by the amplitude of vibration of said element and a frequency determined by the frequency of said vibration, and means for varying the frequency of said vibration while maintaining the amplitude of said vibration constant, said means comprising an output circuit connected to said voltage generating means, phase-shifting 'means connected across said output circuit, and means including a driving coil connected to said phase-shifting means for supplying a driving force to said element, the phase angle between said force and said vibration being adjustable.

5. In combination, a vibratory element, means associated therewith for generating a voltage having an intensity determined by the amplitude of vibration of said element and a frequency determined by the frequency of said vibration, an amplifier having input and output circuits, means including a phase-shifting circuit connecting said voltage generating means to said input circuit, and means for varying the frequency of said vibration while maintaining the amplitude of such vibration constant, said means comprising phaseshifting means connected across said output circuit, and means includinga driving coil connected to said phase-shifting means for supplying a driving force to said element, the phase angle between said force and said vibration being adjustable.

6. In combination, an oscillation generator comprising a vibratory element, an electron dischargedevice input and output circuits connected to said device, means including a drive coil coupled to said output circuit for supplying a driving force to vibrate said element, means including -a pick-up coil for controlling the frequency of current in said output circuit in accordance with the frequency of vibration of said element, and means for varying the frequency of vibration of said element, said last-named means comprising a phase-shifting circuit connected between said pick-up coil and said input circuit, a phase shifting circuit connected across said output circuit, and means for adjustably connecting said drive coil across saidlast phase-shifting circuit, whereby the phase angle between said driving force and said element may be varied.

7. In combination, an oscillation generator comprising a vibratory element, an electron discharge device, input and output circuits connected to said device, means including a drive coil coupled to said output circuit for supplying a driving force to vibrate said element, means including a pick-up coil for controlling the frequency of current in said output circuit in accordance with the frequency of vibration of said element, and means for varying the frequency of vibration of said element, said last-named means comprising a phase-shifting circuit connected between said pick-up coil and said input circuit, a capacitor and a first resistance connected in series across said output circuit, said capacitor and first resistance having a common point, a second resistance connected in shunt to said output circuit, and means for connecting said drive coil between said common point and a variable point on said second resistance, whereby the phase angle between said driving force and said element may be varied.

MILTON S. MEAD, JR.

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