US2033021A - Synchronizing system - Google Patents

Description

March 3, J. F

SYNCHRONIZING SYSTEM Filed Oct. 6, 1930 55 INVENTOR Les-f J lib/f ATTORNEY Wires STATES PATENT castes SYNCHRONIZIN G SYSTEM' Lester I. won, Wilkinsburg, Pa, assignor to Westinghouse Electric & Manufacturing Gerr pany, a corporation of Pennsylvania Application 0mm 6, 1930, Serial No. 486,613,

' A '2 Claims. (01.17%293) My invention relates to synchronizing systems wherein apparatus at one location in asystem may be accurately controlled as to speed with respect to apparatus occupying a diiferent position within the system. More particularly, my invention relates to synchronizing systems of the type wherein the speed of rotation of the apparatus to be synchronized is maintained in an un interrupted state.

It is one object of my invention to provide an improved type of synchronizing system.

Another object of my invention is to provide a synchronizing system capable of maintaining synchronism throughout appreciable variations in load on the synchronized apparatus;

Another object of my invention is to provide a synchronizing system capable of reacting quickly to changes in speed of an apparatus;

whereby to bring it back to synchronism without appreciable time lag. i

Another object of my invention is to provide a synchronizing system of merit employing thermionic devices.

Another object of my invention is to provide a synchronizing system operating through the reaction between a, plurality of frequencies.

Another object ot-iny invention-is to provide a system I whereby a. plurality of synchronizing forces may be controlled by a single synchronizing frequency.

Another object of my invention is to provide a synchronizing system which will be sensitive and dependable in operation.

Additional. objects of my invention will be pointed out in the following description, taken in conjunction with the accompanying drawing} wherein I a i Figure 1 is a circuit diagram of a system illustrating one embodiment of my invention having means for changing over to another enibodiment of my invention.

Fig. 2 is a diagram illustrating, in simplified form, a portion' of the circuit disclosed in Fig. 1.

Fig. 3- is a tubeecharacteristic-curve'diagram for simplifying the explanation of the operation of the system.

Synchronizing systems, in general, are required where it is desired to maintain the speeds of two remotely located apparatus constant.

According to the prior art with which I am such time as a prearranged contact on the apparatus at the other end makes contact to close a circuit which will operate to again start rotation of theflrst apparatus. Inthis manner, the speed 5 of the first apparatus is maintained in synchronism' with that of the second apparatus.-

Synchronizing systems of "the other type embody those systems' wherein the rotation of the app ratus to be synchronized is not interrupted, 10 but the apparatus is maintained in; continuous rotation, and synchronism is obtainedby slightly increasing or decreasing the speedof rotation in the desired direction. The accuracy and dependability of any particular system depends upon 1 the sensitivity of the elementscomprising the circuits and the rug edness of the apparatus embodied therein.

- -My invention relates to a synchronizing system of the second type wherein the speed of the ap- 20 paratusis maintained uninterrupted. In systems of this type, a synchroni channel is generally provided, over which a synchronizing irequency wave is continuously transmitted. This synchronizing frequency is employed to maintain 25 the apparatus at one end of the system in step with the apparatus at the other end, which apparatus is also under the control of the synchronizing frequency.

This type of system, while of generalutility, is very suitable for use in the field of printing telegraphs, facsimile-transmitting systems, television, etc... whereinthe receiving devices must for efllcient reception, be maintained in absolute synchronism with the transmitting apparatus. '35

when employed in systems-of the type referred to above, it is necessary that the synchronizing system shall possess the characteristic of great sensitivity and quick action in bringing about thesmall changes in speed necessary to maintain 40 a synchronous condition between the receiving and the transmitting apparatus. v j An obvious method of doing this is to run a synchronous motor on the synchronizing frequency, but this is often diilicult because the 45 synchronizing frequency may be too high for successful operation of a synchronous motor, if

much power is required of the motor. Another method heretofore proposed is to operate the apparatus to be synchronized by a -50 motor supplied from the ordinary alternating or direct current power supply, and couple to this a smaller motor of the synchronous type which is tobe operated from the synchronizing-frequency supply, the load being adjusted between the two motors in such manner that a large portion of the load is taken care of by the larger motor operating from the power supply, the re:-

mainder of the load being reserved for the synchronous motor. The synchronous motor will thus function to maintain synchronisin between the apparatus at the receiving end and that at the transmitting end.

My method involves an improved manner of maintaining synchronism. It is a known fact that if the winding of a squirrel-cage induction motor is supplied with a direct current, a current will be induced in the squirrel-cage rotor, and a braking action will result because of the reaction between the field produced by the direct current and that produced by the current in-' duced in the rotor, the braking effect increasing with an increase in the direct current in the winding of the motor. This is one phenomena of which I make use in the operation of my synchronizing system and may be referred to as inductive braking.

Another phenomena which I also make use of may be referred to as thermionic braking, the operation of which will be explained in the description of the circuits.

My system is so designed that I may employ both braking effects in the operation of synchronizing, or I may so adjust the circuit as to cause the operation of my circuit to depend upon either the one or the other of the braking effects.

Referring more particularly to the drawing, I have disclosed in Fig. 1,'a schematic diagram of a squirrel-cage induction motor l of the splitphase type, that is, the motor is designed for single-phase operation and is provided with an additional winding 3 in quadrature with the normal running winding 5 for starting purposes. When once brought up to speed, this additional winding 3 is not needed and I, accordingly, arrange to connect the winding in the plate circuit l of a thermionic device 9 wherein the plate current of the tube will be caused to traverse the winding and produce a braking action on the induction motor to a degree depending upon the value of the direct current in the plate circuit of the tube.

Mechanically coupled to the rotor ll of the squirrel cage motor, I provide a frequency device segments 2| constituting alternate north and south poles of the magnet.

A suitable winding 23 on these poles is provided, the extremities of which are connected quency being dependent upon the' number of poles and the speed of rotation of the circular element ll.

The phonic generator [3' is so designed and adjusted that the frequency-generated thereby will be-substantially the same as that of the frequency of the synchronizing wave which. is received upon the input circuit 3| toa thermionic.

device 33. The potential fluctuations on the grid 35 of the thermioniddevice '33 as caused by the frequency transformer 4| The output of the phonic generator l3 and that of the thermionic device 33 are, accordingly, am-

plified by means of audio-frequency transform ers respectively associated therewith, the secondary windings 43 and 45 of which are connected in parallel between the grid 41 and the filament d9 of the thermionic device 9 and constitute the input circuit of the tube 9. I

In order to explain the thermionic braking action which I obtain as a'result of the particular circuit described, I have illustrated, in Fig. 2 of the drawing, a portion of the system of Fig. 1 in simplified form. V r

- Referring more particularly to Fig. 2, therefore, I have disclosed the audio frequency transformers ll and 21 constituting the output circuit of the thermionic device and the phonic generator, respectively connected in parallel across the grid All-and filament d9. Assume, for the purpose, that the frequency, as generated locally by the phonic generator l3 coincided with that of the incoming synchronizing frequency. Under these circumstances, there will be hardly any appreciable current flowing in the secondary-coils Q5 and d3 of the transformers ti and 21, respectively,

since the potentials generated across the coils will be substantially equal but opposite in direction.

The current passing through thesecondary windings will be that due to leakage across the gridfilament path within the thermionicdevice 9 and this will be determined by the bias on the grid 41; Under these circumstances, the load on the phonic generator l3 will be a minimum.

Now let us assume that the frequency-of the phonic generator may shift to such position as to be 180 out of phase with the synchronizing frequency, then the potentials generated across the secondaries of the transformers will be in series, and a heavycurrent will be caused to flow through the closed low-resistance circuit defined by the two secondary windings 45 and 43.

Under this particular set of circumstances, the energy which must be 'produced by the phonic generator will be comparatively great and, consequently, the load on this particular element will 'be a maximum, thus settingup a retarding force on the induction motor I.

By so adjusting the phonic generator with respect to normal rotation of the induction motor that the frequency of the phonic generator will be substantially out of phase with that of the incoming synchronizing wave for normal operation, it will become apparent'that means is thus provided whereby the phonic generator may be caused to exert a braking, or a debraking action on the induction motor, depending on conditions existing at the moment.

'The reaction between the two'frequencies, as explained above in conjunction with Fig. 2, will cause the potential on the grid 41 of the thermionic device 9 to increase or decrease according to the particular phase relationship existing be- 7 tween the two frequencies at any particular if the device is biased in such manner as to act in the nature of a detector, the variable swing of the grid 41 may be employed to vary the current in the plate circuit 1 of the thermionic device 9 in such manner as to produce a braking or debraking action on the induction motor l at the desired moments.

In order to cause this braking effect to operate in such manner as to cooperate with the thermionic braking effect described above, it is necessary that the thermionic device be operated at the upper bend of its plate-current-characteristic curve. At the same time, it is also desirable that the grid be biased negatively to prevent grid current from flowing in the input circuit of the tube.

This condition may be obtained through the use of a thoriatecl or tungsten-filament tube and by impressing a high potential on the plate and a low potential on the filament. In Fig. 3, I have illustrated diagrammatically a plate-currentcharacteristic curve under the conditions specifled, and have shown in what manner the plate current of the tube 9 may be varied in the desired manner.

Assuming a zero-frequency shift to exist between the two frequencies employed in the system, then the voltage on the grid 41 because of the frequency relationship will be zero and the plate current will be that represented by the negative-bias potential on the grid. The value of the plate current may, therefore, be represented by a horizontal line indicated by the reference I numeral 5|.

Under the conditions of maximum shift between the two frequencies, a fluctuating potential will be impressed upon the grid which-under these conditions, will enjoy its maximum swing. I have represented this by a sine wave curve 53 imposed on the grid bias axis 55. The particular shape of the plate current produced thereby will follow a curve 5?, such as that shown in the figure. ,It will be noted, however, that, because of the detector action of the tube, the positive half cycles of the grid potential produce smaller changes in the plate current than the negative half cycles. Consequently, the average plate current may be represented by the broken line 59 which will be of a lower value than the current value representing a zero shift in frequencies.

Since I have shown it to be desirable to operate at a point intermediate the two extremities, the plate current flowing in the coil for normal operation of the induction motor will be represented by the value. shown by the broken line 6| in the figure. i

In Fig. 8, I have not-attempted to illustrate the particular wave shapes of the potentials produced by the reaction between the two frequencies but have merely employed a conventional sine wave for purpose of illustration and explanation.

When referring to the thermionic braking effect, I have shown that, when the two frequencies were in synchronism, the braking action was a minimum. I have also shown that, under the same conditions, the braking action due to the current in the plate circuit of the thermionic device was also a minimum, and likewise, I have shown that, when/the two frequencies were 180 out of phase,' the braking actions due to both the thermionic braking and the inductive braking would be a maximum.

Thus, it will be seen that both braking effects,

under the conditions outlined, cooperative in their action.

If the thermionic device were operated on the lower bend of the plate-current curve, the braking action due to the one phenomena would oppose that of the other. However, it would be possible to so adjust the elements of the system that the braking efiect of the one maybe of much greater force than that due to the other. In which case, the system could be made to operate successfully as a synchronizing system, if desired, even under those conditions.

as an alternative method of operation, the secondary d3 of the audio-frequency transformer 2"! associated with the phonic generator 43 may be connected in series with the secondary 55 of the audio-frequency transformer M associated with the thermionic device 33. To accomplish this, a'switching apparatus may be provided whereby the parallel connection of the two secondary coils may be broken and a series connection provided. When utilizing the series connection, the system cam operate only through the use of the inductive braking eifect, as no thermionic braking action will be produced in the system as modified.

The operation of the modified system to pro duce the inductive braking will be substantially the same as in the previous system first described. However, the grid swing will be twice as great, assuming the values of the potentials developed by the phonic generator and the synchronizing wave are of the same value, since the potentials in the series-connected circuit are added directly. This will permit of a greater variation in the plate current flowing in the circuit of the thermionic tube Q whereby substantially the same degree of synchronizing effect may be obtained as with the system wherein I employ the cooperative eflect oi the inductive braking and the thermionic braking.

lhe operation of my invention may be explained as follows:

The induction motor is first brought up to synchronous speed. A convenient way of doing this is to temporarily switch over the starting winding 3 to the power supply and bring the motor up to a speed where it will accelerate single phase.

The starting winding may then be switched over to the plate circuit 1 of the thermionic device 8. An impedance 65, comprising either a variable 7 resistance, a variable inductance, or a variable capacity in the power-supply circuit, may be employed to bringabout proximate synchronization.

If, for any reason, the load on the motor I causes the speed of the motorto change slightly to an cit-synchronizing speed condition, the system will operate, in the manner described, to either increase the load or decrease the load on the motor I to bring it back to its synchronous condition. This change in the system described by me will be a very rapid one, as the elements employed are very sensitive and quick-acting.

I have, accordingly, described a system which will fulfill the objects of my invention. Many changes may be made which lie within the scope of my invention. I do not desire therefore, to be limited to the details of my invention as I have outlined them, except insofar as is necessitated by the prior art and the appended claims.

I claim as my invention: r

1. In a synchronizing system, apparatus to be synchronized, means for generating a periodic potential of frequency proportionate to the speed of said apparatus, means for supplying another periodic potential of a frequency equivalent to the frequency of said first-named potential when the motion of said apparatus is normal, 9. closed circuit in which said periodic potentials are supplied in series with each other, an electric discharge device having a control electrode and a I plurality of principal electrodes, means for connecting said control electrode and one of said principal electrodes to said circuit in such manner that said periodic potentials are supplied in parallel therebetween and means for coupling said principal electrodes to said generating means in such manner that said generating means is loaded in accordance with the current transmitted between said principal electrodes.

2. In a synchronizing system, apparatus to be synchronized, means for generating a periodic potential of frequency proportionate to the speed of said apparatus, means for supplying another periodic potential, a closed circuit in which said periodic potentials are supplied in series with each other, an electric discharge device having a control electrode and a plurality of principal electrodes, means for connecting said control electrode and one of said principal electrodes to said circuit in such manner that said periodic potentials are supplied in parallel therebetween and means for coupling said principal electrodes to said generating means in such manner that said generating means is loaded in accordance with the current transmitted between said principal electrodes.

LESTER J. WOLF.

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