US1809832A - Synchronous driving system - Google Patents

Description

June 16, 1931. A. M. CUR-ns' SYNCHRONOUS DRIVING SYSTEM Filed Dec.

@jy/M Arron/ver Patented June 16, 1931 UNrri-:DN STATES PATENT OFFICE `USTEN M. CURTIS, 0F EAST ORANGE, NEW JERSEY, ASSIGNOR T0 BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK SYNCHRONOUS DRIVING SYSTEM Application led December 2, 1927. Serial No. 237,346.

. This invention relates to synchronous telegraphy and an object is to increase the reliability and eiiiciency and reducel the maintenance expense of constant speed synchronous driving systems that utilize a vacuum tube oscillator as the source of constantfrequency current. y

In high speed synchronous communication systems vacuum tube regenerative tuning 1o forks are sometimes used as sources of constant frequency waves.` These Waves are applied to a polar relay which vibrates in synchonism therewith and supplies from its contacts positive and negative current alternately to the primary winding of a transformer,

the secondary ofy which is connected to the armature of a synchronous motor. In normal operation vacuum tube oscillators of the type utilized produce a distorted wave due to the presence of even harmonics. The effect of such a distorted wave on the relay is to cause it to remain in one position longer than in the other and to feed an unbalanced cur- Y rent to the transformer. This unbalanced current may be resolved into a desired a1- ternating component and an undesired direct current component which reduces the effective permeability of the transformer core material and causes the transformer to draw an excessive magnetizing current from the relay. This heavy current burns'the relay contacts which as a result require frequent attention. Applicant has discovered that by placing a low pass filter in the output circuit of the vacuum tube to remove the even harmonies from the wave supplied and thus prevent biased operation of the relay, the'transformer magnetizing current is materially reduced and as a result'burning of the relay contacts is to a large extent avoided.

'In the drawings, Fig. 1 disclosesa fork controlled vacuum tube oscillator containing a ilter in accordance with this invention; Figs. 2 and 3 are curves representing the output wave of such an oscillator without and with the filter respectively; and Fig. 4 shows a modification of Fig. 1 wherein lilters are employed in each circuit connecting the frequency setting fork system with a device to be controlled. y

Referring to Fig. 1, the apparatus Within the rectangle represents a complete fork controlled vacuum tube oscillator adapted to supply alternating current of constant frequency to two independent circuits through the output transformers 14 and 15. A relay driving a synchronous motor through a transformer is shown connected to transformer 15 and a similar` apparatus may be operated fromr and 15. The oscillator is adapted to draw L energy for both the filament and plate circuits of the vacuum tubes from a single source 28. Resistances 23, 24 and 2l are connected in series with the filaments of the tubes to reduce the voltage to the proper value. The fila-ments of all the tubes are connected in series and the proper grid-biasing voltage for each tube is obtained by connecting its grid ret-urn lead to such a point in the filament circuit as to utilize the voltage drop in the resist-ances 23, and 24 and the filaments of some of the other tubes.

The resistances 22, 25 and 26 reduce the voltage of power source 28 to the proper values for application to the plates of the different tubes and alsoA serve as protection devices to limit the current iiow in case of a short circuit in the wiring.

Electromagnet 2 mounted at the end of fork l and energized throughresistances 20 .from source 28 is to compensate for the effect on the fork frequency of variations in the voltage of the power supply. Thus if the voltage of source 28 should increase, it would increase the space current of tube 5 and deliver more power to the polarized electro-magnet 3, which would tend to increase the magnitude of vibration of the fork. The increase in voltage of source 28 would, however, also increase the magnetic attraction of electro-l magnet Q ou the fork tines. This has the etllect ot increasiire` the tension in the forli tines and also of increasing the Work done by the tincs iu cutting through the magnetic field of the electromaguet. lioth efiects tend to reduce the aiu plitudc oit vibration and couipensate i'or the stronger driving impulz-scs from magnet 3.

lt is to bc understood that an increase in the amplitude oi'l vibration reduces the 'lirequcncy, and yicc Vversa. ller this reason \'a riable resistance 27 is inserted in the drive magnet circuit 'to malte fine iuljustments in 'frequency by varying the amplitude.

In oiniration.l the motion oit the steel Jforli tiues changes the thu; in the polarized pichup coil 1, which has a permanent magnet core, and develops an elcctron'iotive torce corresponding in frequency to the frequency et vibration oi" the forli. rl"his electromotivc torce. is applied to the grid oit oscillator tube 5 and the amplified energy Yfrom the output oit thc tube is ted baci: through the seconda ry Winding S ot transformer G, condenser 29 and variable resistance QT to drive .magnet 3, which also is permanently polarized by suitable means. When `thc spaces l'ietwc. the pick-i p and drive magnoten and the toi-li tines, are adjusted 'for stable operation, it is founfl that theI amplitude oit viln'a'timi is limited by the oscillator tube 5 which overloads and acts to limit the amount et power applied to tram-:former t and the drive magnet The Wave supplied by tube 5. when the tube is overloaded, is badly distorted, due to the presence chiefly of even harmonics, and may have. a form like that oit the curve in Fig. 2. lit such a Ware were applied to polar relay 1G, it would cause the a rniature of the `rel ay to lie against one coutact longer than the other. That this is the asc may readily be seen from a study oit Fig. Q in which lines 31 and 5:32 above and below the Zero line respectively, indicate the potential required to operate relay 16. Thus at time A the relay would operate to close on one contact and remain in that position until time l when it would operate to close on the other contact. The average lengths ot time during which current l'iows in each direction through the primary VWinding of transformer 18 are theretore proportioiuil to the distances All) and BU. lfhe nct result ot applying current to the transita-mer tor longer periods .in one direction than in the other is to produce an unbalanced direct current in one direction which tends to saturate the core material. As a direct result ot this saturation, the permeabilit?,7 of the transiormer core material is reduced; the inductance ci the primary Winding is reduced, and an increased magnetizing current is drawn from battery 17 over the contacts ot relay 16. The increased current may cause the contacts to corrode much more rapidly than they would if the core were not saturated.

The distortion in the oscillator output Wave may be reduced to a certain extent by increasing resistance 27 so that the amplitude ot vibration of the Yfork is imaiilicient to overload tube 5, but under such conditions the 'fork is unstable and the output power is greatly reduced. Accordingly, it is ttouud preferable to permit the oscillator tube to work overloaded and to inscriJ a low pass filter l() oit conventional type in the output circuit. This filter is designed to cut olin Waves o't frequencies slightly higher than any 'frequency at which the oscillator would normally operate, but to permitthe fundamental Waye to pass With little attenuation. The cut-ofi point ot the lilter Will still be louT enough, however, to greatly attenuate all harmonics so that the Wave applied to the transformer 11 may be practically a pure sine Ware as I shown in Fig. 3. It may readily be seen that the relay 1G when operated by a pure Ware such as that shown in Fig. 3 Would always be held for the same length of time in each position, and that, accordingly;there would be no average unidirectional magnetizing current in transformer 18 to produce saturation and the resultant contact trouble as outlined above.

Although in Fig. 1 the filter 10 has been i inserted between the oscillator tube and the amplifier tubes 12 and 13, two filters 10 may be used as shown in Fig. l, one inserted in eachof the output circuits oi amplifier tubes 12 aud 13. `Where tubes 12 and 13 are overloaded so as to introduce considerable distortion themselves, it would be advantageous to insert the filter in the amplifier output circuits.

lVhat is claimed is:

1. A synchronous driving means comprising a source o't `alternating current waves ot unsymmctrical torni, a relay operated by said Waves to supply current pulses ot alternately opposite polarity over its contacts, an inductive circuit which comprises a magnetic core ot' material the permeability o'i which decreases athigh'magnctizing forces, for producing in response to said pulses ot alternately opposite polarity au altrnating current wave of a. uniform maximum amplitude, and a selective circuit inserted in said source of unsymmetrical Waves to render said Waves symmetrical. in form.

2. A synchronous driving means compris- `ing a source of alternating current Wares of nnsymmetrical i-orm, a relay operated by said Waves to supply current pulses ot alternately opposite polarity over its contacts, au inductive circuit comprising a transformer having a coro olinaterial the pernuaibility o t which decreases at high magnetizi ng forces, ,vor producing in response to said pulses oil" alternately opposite polarity an alternating current Wave of a uniform maximum amplitude,

and a filter circuit inserted in said source of unsymmetrical Waves to render said waves symmetrical in form.

3. A self-oscillatory circuit for driving a relay at a constant speed and in an unbiased manner comprising a vibratory mechanical element, a pick-up coil for deriving energ from said element, circuit arrangements for feeding back energy from said coil to said element to maintain'it in vibration comprising a discharge device amplifier and a drive coil, and a circuit connecting said pick-up coil withsaid relay through said amplifier including a filter between the amplifier and the coil for suppressing harmonics of the frequency of said element.

4. A source of waves of unsymmetrical form, a relay operated by Waves from said source and having contacts associated with a source of direct current, an inductive circuit comprising a magnetic core arranged to control the output current intensity to be supplied with current pulses of alternately opposite polarity from said source of current by said relay, and a selective circuit inserted between said source of waves and said relay whereby said Waves are made symmetrical.

5. A source of waves of unsymmetrical form, a `polar relay operated by waves from said source-and having contacts associated with a source of direct current, an inductive circuit which ycomprises a magnetic core of material the permeability of which decreases at high magnetizing f orces, supplied with current pulses of alternately opposite polarity from said source of direct current by said polar relay, and a low pass filter inserted between said source of waves and said relay whereby said waves are madesymmetrical.

6. A source of waves of unsymmetrical form, a polar relay operated by Wavesfrom said source and having contactsv associatedv with a source of direct current, a transformer circuit comprising a core of material the permeability of which decreases at high magnetizing forces, supplied with current pulses of alternately opposite polarity from said source of direct current by said polar relay, and a low pass filter inserted between said source of waves and said relay whereby said waves are made more symmetrical.

7 A source of waves of unsymmetrical form comprising a vacuum tube oscillator the fundamental frequency of which ma be adjusted between set limits, a low pass lter connected to said source having a cut-off point higher than the upper frequency limit of said source but lower than twice the lower limiting frequency of said source, a vacuum tube amplifier for amplified waves received from said filter, a polar relay operated by the amplified waves having an armature movable between two fixed contacts, a transformer havlng a primary winding with a mid-tap,

the ends of said primary winding being connected to said respective fixed contacts of said relay, a source of direct current connected between the mid-tap and said armature, a secondary winding on said transformer, and a synchronous motor connected thereto.

8. In combination, a source of electric oscillations comprising a thermionic vacuum tube having an input circuit and an output circuit, a vibratory element, magnetic driving means controlled from the output circuit of said tube for vibrating said element, means responsive to the motion of said element to produce an electromotive force connected to theinput of said tube, a low pass filter connected to the output circuit of said tube, a polar relay operated by waves received from said tube through said filter and having a contact movable between two fixed contacts in response to said waves, and an inductive circuit supplied with current flowing in one direction therethrough from the movable contact when it is in one position and in the opposite direction when the movable contact is in its opposite position.

9. A source of constant frequency alternating current, a filter connected thereto for removing even harmonics from the wave produced by said source, a plurality of vacuum tube amplifiers, the input circuits of which are connected to the output circuit of said filter, a relay connected to the output circuit of each amplifier, an inductive device having a core subject to magnetic saturation, a source of direct current, contacts on said relay, and connecting means between said contacts, said source and said inductive means whereby said relay in vibration supplies current pulses of alternately opposite polarity from said source of current to said inductive means.

In witness whereof, I hereunto subscribe my7name this 30th day of November, A. D. 192

AUSTEN M. CURTIS.

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