US2793293A - Vibrating reed-type frequency standard - Google Patents

Description

May 21, 1957 R. J. EHRLINGER EIAL VIBRATING REED-TYPE FREQUENCY STANDARD Filed May 6, 1954 INVENTORS ROBERT J. EHRL/NGEH HARRISON R LAMBERT ATTORNEYS United States Patent O VIBRATING REED-TYPE FREQUENCY STANDARD Robert J. Ehrlinger, Baltimore, and Harrison R. Lambert, Glen Burnie, Md., assignors, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application May 6, 1954, Serial No. 428,147

4 Claims. (Cl. 250-36) This invention relates to a vibrating reed employed as a frequency standard.

Present day frequency standards for use in the 400 cycle per second range usually use either a tuning fork or crystal for the frequency stable element. These frequency standards, however, are more accurate than neces sary for most practical applications, are non-adjustable and are relatively expensive to manufacture.

It is an object of this invention, therefore, to provide a frequency standard which is simple in construction, relatively inexpensive to manufacture, adjustable, and accurate enough for most practical applications (if/2%).

Another object of this invention is to provide a vibrating reed having the shape of a cross and spaced between a pick-up and a driving magnetic circuit, the pick-up magnetic circuit being oriented 90 degrees from the driving magnetic circuit,'and operating in conjunction with the cross arm member of the vibrating reed.

Other objects and advantages of this invention will become apparent upon consideration of the following detailed description and the appended claims, taken in connection with the accompanying drawings, in which:

Fig. 1 is a plan view of the layout of the magnetic circuits and the reed;

Fig. 2 is a side elevation of Fig. 1;

Fig. 3 illustrates the shape of the reed employed; and

Fig. 4 is a schematic diagram of the driving and pickup circuits.

Reference is now made to Figs. 1 and 2 wherein the vibrator assembly is shown to comprise a mounting plate on which a pick-up magnetic circuit 11, a driving magnetic circuit 12, and an adjustable vibrating reed 13 are mounted.

The pick-up magnetic circuit 11 comprises an annular coil 14 having terminals 1 and 2, and is mounted on a magnetic core assembly 15. The core assembly 15 consists of a central permanent magnet section 16, and a pair of magnetic iron legs 17 and 18. As shown in the drawing, the axis of the coil 14 is perpendicular to the plane of the base 10.

The driving magnetic circuit 12 comprises an annular coil 19 having terminals 3 and 4 and is mounted on a core assembly 20 in such a manner that the axis of the coil is parallel to the base plate 10 and perpendicular to the axis of the coil 14. The core assembly 20 comprises side legs 21 and 22, and a central section 23 on which the coil 19 is wound. All the sections of the core assembly 20 are composed of magnetic iron.

The magnetic circuits 11 and 12 are each mounted on the base 10 by means of the pairs of bolts and clamps 24 and 25, respectively, or in any other suitable manner. The reed 13 is disposed between the circuits 11 and 12 in a manner hereinafter to be described.

Referring now to Fig. 3, it is seen that the reed 13 is in the shape of a cross having legs 26 and 26a, and integral cross arms 27 and 27a. The slots 28 and 29 have been provided as a partial compensation for frequency drift due to temperature variation. A hole 30 has been Patented May 21, 1957 drilled or punched at the free end of the leg 26a to provide a means for mounting the reed between the magnetic circuits. The reed is composed of a magnetic material.

The reed mounting assembly 31 comprises a C-shaped bracket 32 secured in any suitable manner (not shown) to the mounting plate 10, and the bracket 32 is provided with a horizontal smooth surface 33. A rotatable shaft provided with a threaded portion 34 and a head portion 35 is rotatably mounted between the opposite walls of the bracket 32 and is prevented from longitudinal motion by means of a washer 36. A travelling block 37 having a groove 38 at the top thereof, and an internally threaded bore therein for receiving the threaded portion 34 of said shaft, is arranged for longitudinal motion on said shaft along the surface 33 of said bracket 32 when the shaft is rotated by means of the head portion 35 of the rotatable shaft. A projection 39 extends vertically from the bracket 32 to form a solid support against which the reed 13' is pressed by lateral motion of the block 40. Lateral motion is imparted to the block 40 by means of the inclined surfaces 41 on the bracket 32 and the block 40 (see Fig. The block 40 has a slotted and oversized hole which allows lateral motion of the block 40 as the screw 40a is tightened down. Thus, block 46 and the screw 40a are used to clamp the reed 13 against the projection 39 after it has been adjusted to the proper length by the screw 35. The reed 13 is secured at one end to the trave1- ling block 37 by means of a pin 42 passed through said block and the hole 30 in the reed 13, and is snugly supported at an intermediate portion of the leg 26a between the block 40 and projection 39.

The effective length of the reed is the distance from the extreme end of the leg 26 to block 39. It is seen, therefore, that the effective length of the reed may be varied by rotating the shaft and thus causing the travelling block 37 to move longitudinally and thereby cause fore and aft motion of the leg 26a.

The reed 13 is designed to operate between the two magnetic circuits 11 and 12, respectively, which comprise the pick-up and driving circuits. The legs 26 and 26a of the reed 13 are dimensioned, therefore, so that they will be adjacent and opposite the legs 21 and 22, respectively, of the core assembly 20, while the arms 27 and 27a are dimensioned so as to be adjacent and opposite the legs 17 and 18, respectively, of the core assembly 15,. By means of this arrangement, coil 14 will be affected almost exclusively by the reed cross arms 27 and 27a which complete a flux path through the core assembly 15, while energization of the coil 19 afiects almost exclusively the reed legs 26 and 26a which complete a flux path through the core assembly 20. If the reed 13 were designed regular in shape, the legs of the two magnetic circuits 11 and 12 would be diametrically opposite and the system would oscillate at a frequency independent of the reed, but dependent on the inductances and shunt capacities of the pick-up coil 14 and the driving coil 19. Thus, the pick-up and driving coils 14 and 19 have been oriented degrees apart in space relationship. As a result, flux generated by the driving coil 19 will not link the turns of the pick-up coil 14 and the frequency of oscillation of the system becomes a function of reed vibration only.

In order to decrease frequency drift as the temperature of the reed varies, a thermostatically controlled heater 65 is employed to stabilize the temperature of the reed at a desirable operating temperature.

The amplifier for the vibratory system of this invention is shown in Fig. 4 and it includes a triode 43 in the input circuit, and a triode 44 in the output circuit. The triode 43 consists of a plate 45 connected to the 13+ supply through the plate resistor 46, a cathode 47 grounded through resistor 48 and a control grid 49. The pick-up coil 14 is coupled to the grid across the terminals 1 and 2. The output from the plate 45 of triode 43 is coupled across the grid biasing resistor 59 of the triode 44 through the coupling condenser 5%. The triode 44 comprises a plate 51 connected to the B+ supply through the variable condenser 52 and driving coil 19, a cathode 53 grounded through resistor 54, and a grid 55 coupled to the grid biasing resistor 59. The. driving coil 19 is connected in the output circuit of the triode 44 across theterminals 3 and 4.

As a criterion for oscillation, the current through the driving coil 19 must be displaced approximately 90 degrees from the induced voltage in the pick-up coil 14. This criterion is arrived at by tuning the driving coil with the variable condenser 52. An initial surge of current through the driving coil 19, when voltage is applied from the B+ supply starts the reed vibrating. Since the permanent magnet 16 inthe pick-up magnetic circuit 11 has created a magnetic field, movement of the reed varies the reluctance of the air gap between the reed and the end of the legs 17 and 18 of the magnetic core assembly. Assuming the flux variation due to vibration of the reed is approximately a sinusoidal function of time, the voltage induced in coil 14 is a sinusoidal function of time which is amplified by triodes 43 and 44 sufiiciently to control the current flowing through the driving coil 19. With the proper direction of current flow through coil 19, established by the appropriate connections to the B+ terminal and plate 51 of triode 44, the phase of the sinusoidal current in coil 19 and the resultant force on the reed may be altered sufficiently to sustain the vibration of the reed.

While only one preferred embodiment of this invention has been disclosed, many modifications, equivalents and alterations will become readily apparent to those skilled 0 in the art. It is the intent, therefore, that this invention be limited only by the prior art and by the scope and spirit of the appended claims.

greases We claim:

1. A vibrating reed frequency standard comprising: a pick-up magnetic circuit and a driving magnetic circuit spaced 90 degrees from said pickup magnetic circuit; a vibrating reed disposed between said magnetic circuits, said vibrating reed having the shape of a cross having a leg and a perpendicular cross arm, the leg of said reed being adjacent and opposite said driving magnetic circuit so that flux of said circuit traverses said leg, the cross arm of said reed being adjacent and opposite said pickup magnetic circuit, so that flux of said pick-up magnetic circuit traverses said cross arm means for producing flux in said driving magnetic circuit to move said reed; means responsive to the movement of said reed for inducing a voltage in said pick-up magnetic circuityand means for amplifying said induced voltage for altering said induced flux in said driving magnetic circuit.

2. The combination as defined in claim 1 wherein the cifective length of said reed is adjustable.

3. A vibrating reed frequency standard comprising: a first magnetic core, a portion of which is a permanent magnet; an annular pick-up coil mounted on said core; a second magnetic core, a driving annular coil mounted on said second core; the magnetic axis of said first core and said pick-up coil being arranged normal to the magnetic axis of second core and said driving coil; a reed having a first portion in the flux path of said pick-up coil; and a second portion perpendicular to said first portion in the flux path of said driving coil, said first and second portions of said reed being integral and in the shape of a cross.

4. The invention as defined in claim 3 wherein the effective length of said reed is adjustable.

References Cited in the file of this patent UNITED STATES PATENTS 1,821,181 Gunn Sept. 1, 1931

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