US2482444A - Alternating current synchronizing apparatus - Google Patents

Description

Sept. 20, 1949.

Filed Aug. 31, 1946 M. TOUSSAINT 2,482,444

ALTERNAT ING CURRENT SYNCHRONIZING APPARATUS 2 Sheets-Sheet 2 o 1 e 3 4. s a r a 9 m n 12 1a 14 75 Mae/c5 7o'uaswlvr Patented Sept. 20, 1949 ALTERNATING CURRENT SYNCHRONIZING APPARATUS Maurice .Toussaint, Paris, France, assignor to Societe Francaise Radio Electrique, a corporation of France Application August 31, 1946, Serial No. 694,405 In France June 2, 1945 I Section 1, Public Law 690, August 8, 1946 Patent expires June 2, 1965 6 Claims.

An arrangement in accordance with this invention makes use of a cathode ray phasemeter,

of a type known per se whose spot remains stationary if the two frequencies are synchronised but describes slowly anarc of a circle when the relative phase changes.

' The invention is illustrated in and explained in connectionwith the accompanying drawings in which Fig. 1 is a general schematic diagram of the phasemeter and associated automatic synchronising arrangement; Figs. 2, 3 and 4 are explanatory graphical figures relating to the operation of the arrangement of Fig. l; and Fig. 5 is a schematic representation of a preferred form of ratchet driven reverser employed in the synchronising arrangement.

Referring to Fig. 1 suppose F and F are two frequencies to be maintained in synchroriismF being for example, the master frequency and F" being a secondary or slave frequency to be synchronised'with it. The frequency F is split into two quadrature components which are applied with equal amplitude to the mutually perpendicular pairs of deflecting plates of a cathode ray tube one component to each pair. This quadrature application will of course cause thecathode' ray to trace a circular path on the screen. In Fig; 1 the two equal amplitude quadrature components of frequency F are provided by the slave generator 3, one being applied directly and the other being applied through a suitable 90 phase shifter 4. The control electrode of the tube is biassed so that the electron beam is normally cut off. The cut-off bias on the control electrode is overcome periodically for a very brief impulse in each cycle by alternating voltage applied from a generator 2 or other source of the master frequency F, so that the beam appears during this short portion of each cycle of frequency F and the spot on the screen traces an arc of a few degrees during a fraction of the period I/F, the fraction being determined by the amplitude and waveform of the voltage applied to the control electrode from 2; By reason of the phenomenon of persistence of vision there appears on the screen'a trace in the form .of a small arc-which arc is reduced practically to a spot by the use of a suitable wave form'from 2-which remains stationary if the frequencies F and F are absolutely in synchronism but which moves in one direction or the other with an angular speed equal to 21r(F'F) if the frequencies are not synchronised.

The phase meter indications above described could, of course; be utilised by an observer controlling manually the frequency of the slave generators until the spot appeared stationary. The present invention haslfor its object to provide an automatic arrangement which will provide the necessary control for synchronising without needing visual observation and manual control.

' To this end in accordance with the invention there is provided adjacent and parallel toethe screen of the tube an opaque circular disc 5 having a circular aperture 6 Whose diameter is sensibly larger than the length of the spot on the screen and whos-eradial distance fromthe centre of the disc is substantially equal to the radius of the circular path of the spot on the screen, the disc and screen being co-axial. Behind the aperture in the disc is a mirror reflector 1 fast with the disc and serving to reflect the image of the spot on to an axially arranged photo-electrical cell 8: w

The disc .5 is driven by' a reversible electric motor l2 through step-down gearing l3 giving a considerable gear ratio. When the spot on the screen is opposite the aperture the photoelectric cell is illuminated and controls through a suitable amplifier 9, and a relay In an electro-mechanical system H (which'will be later described herein) whereby the reversal of the motor i2 is controlled.

As will be seen more clearly later. if the spot remains stationary on the screen of the cathode ray tube the disc 5 will describe alternately equal angles slightly inferior to 360 in both directions of rotation. If the angles of rotation on of the disc be plotted as ordinates against time if, this condition is as represented by the toothed curve of Fig. 2.

If, however, by between F and F ment of'rotation (much disc) the duration of rotation of the disc in the direction of spot rotation will be longer than in the opposite sense. This condition is as represented by the curve of Fig. 3 where the angles of rotation at are again plotted against time, t. To simplify explanation thegraph of this figure has been drawn on the assumption-made purely for convenience and as an example-that the spot moveswith an angular speed equal to one-third of the speed'of rotation of thedisc 3,'the spot and aperture 6 being in coincidence at the origin of the graph. i

- On this assumption, the first coincidence (after the origin) between thespot and aperture will reason of lack of synchronism the spot has itself a slow moveslower than that of the and this cycle of operations will repeat itselfzperiod equalto 2 2 5 9, gebeing the corresponding period when, thespot is sta;

periodically with a tionary.

The arrangement is accordingly utilised to secure automatic synchronisation of. the two. generators (2, 3) by controlling the speed of a a shaft I 5 of the generator 3 throughesuitable re; duction gear I4 from the motor I2, teamma e trol operating as suitable frequency varying device of known type to vary the frequency of thegenerator 3 in the direction required to annul any lack of synchronism. Any difierence betweenthe angle-turned by the disc inonedirection andrthat turnedin the other will thus tend to diminishthe lack of synchronism until proper synchronismjs re-established. The resultant angle through which the disc will have turnedfinally before syn: chronismis established will be .equalto that which wouldhave been necessary .for manual control-to bring the two generators to synchronism taking into account Figure 4 represents for example fluctuations .of the-angle a the interval of time which occurs between the departure fromsynchronismand re: establishment; during this interval the angle throughwhich the disc the example chosen.

The above described arrangement will work satisfaotorily if the natural stability of the two generators is inherently sufiicie'ntly good :to ensure 1 that rapidand important changes soft.- fre-. qu'ency will not occur. In practice the speed of rotation of the disc is chosen in such a manner that in-the course of one period ofrotationthereof the maximum phase difference likely :to occur bee tween-the two-frequencies does not exceed about of this period: The arrangement. above 11E: scribed has the minordefect that a very' small variation of the order of /lOd-Of this periodcan occur inthe frequency-0ttheeslave generator-t This defect, however; may-be easilyavoided-by providinga little play-in the control arrangement for the slave generator; e. A g. by using eat known typeotdrive such as that employed-inthe cinema. Theautomatic reversal of -the direction of rotationof the motor I2; Fig. I is efiectedby a re'verser' I I controlled by the amplifier. 9.-- Ree ferring to Fig. 5 which'shows a preferred-form forthe reverser I I this comprises a eommutatorlhave ing arr-insulating shaft on which isa conductive sleeve-cut away by a double seriesof insulating spaces 25. With this commutator are associated brushes I6, I1, I8 which servewiththecommm tator as a reversing switch and-through which the motor I2 is energised.- The-commutator. is, driven bye-ratchet wheel I Qandthe arrangement of -the insulating spaces 25 andottheteeth of the .wheel I9 are such that displacement from. one tooth to the next causes-a-reversal of themoton- Controlof the ratchet wheel is efiectedby -an-.electro-. magnet -23 -excited bycurrentscontrolledby the relay I0.'(see.Fig.1), in thebutput. circuit of..- the amplifier 9.- This electrol-magnet acts on .an. armature 22 pivoted on an axis 0 and having'lan abutment K-operating against a stop (not shown) to limit theireturn action. or the spring lls The of course i .the gear a ratio involved.

will have-turned is 571: in

armature 22 drives the ratchet wheel I9 through the striker member 20.

The invention has many applications notably to radio diiifusionknetwprkslforjgthe control of stations therein in accordance with a central control frequency fed either over lines or pilot or other radio transmission or in any other way.

W at 1 aim 1 A system for automatically synchronizing the frequency of master and slave generators supplyingperiodic wave outputs comprising in combination, a catl ode ray oscillograph having a screen and electrode means and means applying to.said;electrode,- means wave energies from said generators to produce on the screen a small arcuate luminous spot related in length to the per i odpf, the output wave of the master generator and, under conditions of non-synchronism, having-apparent motion whose speed is proportional to, and in one or the opposite direction dependent oa hes ea Q he. q a t of t e. fr uenc es. a di pa lle t he S ree avinsla circuleeeaer: ire iiehtl lareerihen ez e land et rad al. distance substantially qual to the adial glis tance tt ie e c smieen n rea liher wii or ta n e. dis}; ab ut: 3. 311 ho ele t c l elll ana' t rc eu tsaid el ei e. ro itiene ece v lls l efl eitll I S leem? ur i grq at eaoi a lsls l-l shtrefl arrests for reflecting the light of; the spo merging hrou h aidzapert tezqntesd e lteeslz eee c iic le i-fir a q qeitaf ms naileeslers eenerater mic. XEQWQIlElIl-s the master e -"le atori-v Ae stem. weerdi e Qc lara; 1 1 means for neemallr: s irin ;iqteasle eqtmeera p teetie tq blo in catheqe arraaqr p which e means elai e ly nerware recess-ire 512c eene ater la n iesl lieMemoiremes? resell: later during a fraction of ;its.-peripgl tq qlgpgg l c rod o unh ckltheicathpdexaxand; v awar f qmt helcther: s illates rtQ :Q 1, lf91g 9, ause tatiqnro i he seat ng qilnumier ne 111W: nst-said r.a ialt. i ta1. e-.=v

elsx temtaccerdin i ecl m 1.;in; which-the meanes qe otatins t e Jainflsdes ealtexnete the piirqt en t th ne atiensr i esh eleetr ha hem c l ist ql lai ro ating he is i lu 'e ers rr aidtrere i 4. isl t-c me .astene yiz m atqeetp qtt vina he mmnta er .a ,d.- le tro agne icrmeac s nliee cen rpl..o .the.c.e l ionsten ihcaethecammuietqrr A ys emae pr inerec a m- 1 .;wh i.-. he m ansr-b inein ther al en rato 0.531}: hr eiz nc ud i .l iea el sir sxi ic ntrolla tipn be;

insapplied until a-predeterminmi smell eneriu a fici ntsnlaya etm eyehtiany "z; frornj ynchrpnismmoccurs;

6.; In co bina ion, iinjasy temi n au emaiicala y maintainins.synchreniaatisn between. avgliaa of. stabilized frequency and; a volta e eni:

said stabilized .rrelmeneytbuttwliosetphasel ensis torvar lowly as alfunctiouoatim i a cathederal;

tube havingaiwehnelt electrode-negat velyrpolari iz edsosas-to bioehthetulge. me nsror nble kinethe .tubeat said; stabilized frequency, to ccausveefll luminous spot; to. appear periodicallysonthescreen; of..the tube, twopairs .ofrdefleetion-plates in space quadrature andmeans for..-impressing,equal lyol te. ages inphase quadratureat the servient frequency! OliiSaid. pairsof plates so as tomoduceia disp1aee= m'entofsthespot alongialcircumferencei aidiskzont the same axis-as thatioflsaid circumferenceihavs ing an aperture located at a, distance from the center of the disk equal to the radius of the circumference, a mirror, a motor for driving the disk, by means of a reduction gear at a speed substantially above that of the spot, a photoelectric cell located along said axis so as to be excited from the image reflected by the mirror when the aperture of the disk passes in front of the spot, a relay controlled by the cell and adapted to control rotation of the motor for each successive excitation, alternatively in one direction and in the other, and control means for the servient frequency comprising elements controlled by rotation of the motor through a reduction gear, said reduction being chosen in consideration of the 15 time constant of the control means so that a rotation of the disk of 360 in the same direction is 6 insuflicient to reduce in any appreciable manner at existing difference between the two frequencies, but such that this difference is suppressed by an accumulation of the average effects when the algebraic sum of the angles transversed by the disk in one sense and in the' other attains a predetermined value.

MAURICE TOUSSAINT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Geyer Apr. 16, 1935 Number

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