US2256482A

US2256482A - Data transmission and control system

Info

Publication number: US2256482A
Application number: US83844A
Authority: US
Inventors: Eric J Isbister; Francis L Moseley
Original assignee: Sperry Gyroscope Co Inc
Current assignee: Sperry Gyroscope Co Inc
Priority date: 1936-06-06
Filing date: 1936-06-06
Publication date: 1941-09-23
Anticipated expiration: 1958-09-23

Description

Sept.'23, 1941. E. J. ISBISTER ET AL 2,256,432

' DATA TRANSMISSION AND CONTROL SYSTEM Filed June 6, 1936 4 Sheets-Sheet i j TRANSMITTER 1 RECEIVER 2 1g: 1

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- I PHASE SHIFTER FIXED 5 SPEED PHASE SHIFTER [7 22 DRWE 3 191:27 l TRANSMITTER I I REGENER /5 FRE.) SELECT. '/4 SELECT. DET- J MOTOR Fobl gw 66 Doug, NET. NET, r100. CONTROL: MOTOR l 7 26 .smeu; 42 45 TO HMP. I 5 /6 3pm /8 2 A MULTIPLE PHASE SHIFTER 20 FREQUENCY GEN.

l FIXED RECEIVER SPEED RECENER 5 TRBNSMITTER72 DR'VE K H TRANS r v 5 I l H i a I 5| SELECT. MULTIPLE I I NET- FR W NETWORK; 77 mum I A B TRgNS. TO OTHER $65K???) Rs 7 [m0 J /8BI6TER 7/ fRmvgls L ELEY T0 omen mans Z f! 4 THEIR ATTORNEY Sept. 23, 1941. E. J. ISBISTER ET AL 2,256,432

DATA TRANSMISSION AND CONTROL SYSTEM Filed June 6, 1956 4 Sheets-Sheet 2 .5 PHASE GEN I PHASE GEN INVENTORS [Ric J. ISBISTER @8 S N L /7 RRNC'S OSELEY THEIR ATTORNEY.

P 23, 1941- E. J. ISBISTER ET AL 2,256,482

DATA TRANSMISSION AND CONTROL SYSTEM Filed June 6, 1956 4 Sheets-Sheet 5 I INVENTORS [Ric J/S'BISTER 3'15 fign/vc/s L./70sEL Y P E. J. ISBISTER ET AL 2,256,482

DATA TRANSMISSION AND CONTROL SYSTEM Filed June 6, 1936 4 Sheets-Sheet 4 THEIR ATTORNEY Patented Sept, 23, 1941 1. UNITED I STATES- PATENT OFFICE Eric J. Isbister, Brooil yi ffrl Francis L. Moseley,

Pelham, N. Y., assignors to Sperry Gyroscope Y Company, Inc., Brooklyn, N. Y., a corporation of New York Application June 6, 1936, Serial No. 83,844

This invention relates, generally to data transence, more particularly, to a novel variable phase, two wire data transmission and control to select the returning signal and detect its phase 12 Claims. (01. 111437) position for use either in operating a follow-up indicator or, through use of a torque amplifier, to control a servo motor'to effect the positional control of a controlled object, such as a searchsystem. light.

\ Y Data transmission systems, i. e., electrical sys- Another object of the present inventi li tems employed for transmitting various data such in the provision of a novel data transmission and as angular data or data that are susceptible of control system of the above character that is indication on a suitable sheet, card or other entirely self-synchronous and continuously rotatmember having relative movement with respect l0 able, the said system requiring but one frequency to a pointer or other designating means, as per channel, and being adapted to provide addiheretofore constructed, have generally required tional channels, as desired, over the same pair of five or more wires extending between the trans- Wires by e p y g Corresponding tio al Iremitting or field station and the receiving or cenquencies at the transmitting and receiving ends, tral station. The use of live wires not only e e dditional freq encies being separated greatly increases the installation and mainfrom each other and from the frequency of the tenance expense, but ofttimes five wires are not first channel by the use of suitable filters. available for us in transmitting data, as dur- Still another object of the present invention ing army maneuvers, when it is not practicable is to provide a novel data tranmissionand conto string five wires from a transmitting station, trol System Of the above character that 5 e sy such as an outpost, to a receiving or central stato operate and is reliable in use, the said sy tem tion which may be several miles away. Also, having a small and compact transmitter that such five-wire systems are particularly suscepan be readily carried from place to place by tible to all kinds of interference picked up in one man. the transmitting lines. It therefore becomes Other objects and advantageswlll become aphighly desirable to provide a two-wire data transparent from the sp ifi ati n, ta en "in connecmission system, and one in which ordinary teleti011 With, the accompanying aw n s wherein phon wires may be used for transmitting the one embodiment of the invention is illustrated. desired data. such wires being usually available 1 is a sc ematic view showing of a sin inmost locations. channel, two-wire data transmission system of The principal object of the present invention this invention arranged for manual pis to provide a novel, reliable and easily oper- Fig. 2 is a w g di of ey e 0! ateddata transmission and control system, which g. system employs but two wires extending between 3 is a Schematic w Showing of a yst m the remotely located transmitting and receiving similar to that of Figbut providingfbr autopoints. matic instead of manual follow-up.

Another object of the present invention lies Fig. 4 is a wiring diag a the System 0! in the provision of a novel data transmission 'and control system of the above character where- Fig. 5 is a schematic view showing a multip in a variable phase constant frequency signal channel, e date tia-nsmissien Sys mis employed for transmitting the desired data a Wiring diagram f' system 1 from the transmitting point'to, the receiving point. Similar characters of reference are employed Still another object of the present invention is in the above Views 0 indicate P I DS to provide a novel data transmission and con- P ts- 2 trol system of the above character having means Referring ow to Fig. 1 of the drawin in for producing a synchronizing signal, preferably connection with a brief description 0! Single of low audio frequency, that is sent out from cl'lelimel System ed o manual. Or'hand the receiver to the transmitter, at which latter follow-up, the reference nu eral I desi nates means is provided for "converting such signal to the t itte as a h whereas t e refera higher and difierent frequency of variable ence numeral 2 designates the receiver. The phase position corresponding to the data transreceiver 2 comprises a constant speed drive motor mitted, and then sending it back to the receiver, 3 that is connected to drive a synchronous genthe latter being so constructed and arrangedas erator 4 that supplies a single phase voltage of low or timing frequency through leads [to a line coupling or selecting network 6. From the network 6, the single phase voltage of timing frequency is supplied to a. transmission line I of any desired length, and may be a commercial telephone line. At the transmitter end of this line a line balancing or selecting network I4 transfers the timing frequency to a frequency doubler I5 which converts the single phase voltage to one of double frequency and supplies the same to a network I6 that serves to break up the double frequency potential into three 120 components. This three phase different or double frequency output is fed to the three phase winding of a. phase shifter device or transmitter selsyn I'I whose single phase Winding is coupled to an amplifier I8. This amplifier makes up the losses incurred in frequency doubling and conversion to three phase and also serves to bring the outgoing variable phase different frequency signal to a voltage level suitable for transmission over the line I. The amplifier output is coupled to the line through the selecting or line balancing network I4 which serves to separate the incoming low frequency voltage from the outgoing different or double frequency signal voltage. At the receiver, the selecting network 6 separates the doubl frequency signal voltage of variable phase from the timing frequency voltage supplied from generator 4 and couples the signal voltage to a detector I II. This detector is supplied with a second single phase voltage of twice timing frequency from the phase shifter device or receiver selsyn 20, similar to Selsyn I'I. Selsyn is supplied with three phase voltage of double timing frequency by generator 4. The output of detector I9 is connected to a zero center meter 2|.

In -operation, rotation of the transmitter selsyn handwheel 22 causes the single phase,

double frequency output or signal potential to be shifted in phase one degree for each degree the rotor of device I1 is turned. This signal potential, after passing through line I and terminal apparatus, is applied to detector I 9, where it is compared as to phase with the output of receiver selsyn" 20. If the transmitter and receiver "selsyns are in correspondence, the meter 2| will show a zero reading indicating angular correspondence of the transmitter and receiver selsyns, but on the other hand, if the meter pointer moves off center, the receiver handwheel 23 must be turned to the right or left, depending on the direction of the movement of the meter pointer 24, to bring the pointer back to zero, corresponding to synchronous positions of the transmitter and receiver selsyns. These selsyns ar shown provided with relatively movable data card and indicator means 25 and 26, whereby data received corresponds to that transmitted.

The wiring diagram of the system of Fig. 1 is shown in Fig. 2 and in this latter figure it will be noted that the multiple frequency generator 4 is shown in two parts, i. e., part 4' for generating the timing frequency voltage and 4" for generating three phase voltage of double timing frequency. Thus, if 4' produces 300 cycle single phase current, for example, then 4" will produce 600 cycle three phase current. The selecting network 6 consists of a frequency bridge tuned to the operating frequency of the timing single phase output of generator part 4. This bridge has a reactance arm 8 and a resistance arm 9, the arm 8 acting as a pure resistance at the timing frequency and being exactly balanced by resistance arm 3, whereby equal and opposite currents flow from lead 5 into the primary winding halves I0 and II of transformer I2, so that the current from generator part I does not induce voltage in the secondary of transformer I2 and hence does not apply voltage to the grids of detector tubes I3 and I3. Hence, the output of generator part 4 is supplied to line 'I with substantially no loss and is conducted to the transmitter I, at which the timing frequency voltage passes through the selecting or line balancing network I4, consisting of adjustable condenser 21 and resistance 28, in parallel, and through the primary of trans-- former 23, thereby applying a voltage to a full wave rectifier 30 of the frequency doubler I5.

This rectifier 30 is connected through a resistance BI and condenser 32 to the primary of a transformer 33., The condenser'32 serves to remove the D. C. component produced by the rectifier 30, but permits both halves of the A. C. wave to pass through the primary of transformer 33. to cause all negative voltage peaks to become positive peaks and thus furnishes transformer 33 with two positive peaks for each positive peak supplied by the incoming timing frequency voltage. This double number of positive voltage peaks provides a different or double frequency voltage from the timing frequency, which voltage passes through the single to three phase network IG, where it is broken up into three 120 components and is then supplied to the threephase rotor windings of the phase shifter device or transmitter selsyn I'I. As the rotor of this device is turned by means of handwheel 22, each of its windings couples more or less closely in turn with the single phase winding 34 of this device or selsyn," and since the mechanical distribution of the three-phase rotor windings is exact and the magnitudes and phase positions of the voltages supplied to these windings are .in correct phase relation, the output signal voltage appearing across the winding 34 shifts in phase one degree for each degree of rotor movement.

Amplifier I8, consisting of triode 35 and the usual associated apparatus, raises the signal output voltage of selsyn H to a value suitable for transmission over the line I, to which line this voltage is fedthrough transformer 36, leads 31 and selecting or line balancing network I4. Network I4 is adjusted so as to just balance the impedance of line I, whereby current from leads 3! divides equally in the two halves of the primary of transformer 29, flowing in opposite directions therein so as not to apply the double frequency signal voltage to the rectifier 30.

At the receiver 2 this different or double frequency, variable phase signal voltage passes through the selecting network 6 and transformer I2 and is applied to the grids of detector tubes I3 and I3 of detector I9. The grids of these tubes are also supplied with a double frequency variable phase voltage from generator part 4", this voltage passing from part 4" to the threephase windings of phase shifter on receiver selsyn 20, through single phase winding 38 thereof and transformer 39. When the voltage across the secondary of transformer 39 is out of phase with the signal voltage across the secondary of transformer I2, the vector sums of these voltages reaching the grids of tubes I3, I 3' are equal and therefore each of these tubes Thus, the rectifier serves, 'in effect,-

(biased as detectors) draws the same amount of the ends of resistor 46 and the meter 2| reads zero at the center of its scale.

When, however, the incoming double frequency, variable phase signal voltage is shifted in phase by reason of movement of handwheel 22 of transmitter selsyn l1, the 90 voltage relation of the voltages in transformers 39 and I2 is disturbed and the vector sums of these voltages reaching tubes |3and l3 are no longer equal, and hence unequal plate currents flow in the two halves of resistor 40, producing a net unbalance voltage between the ends of this resistor and causing the pointer 24 of meter 2| to move to one side of the zero position. The receiving operator now turns the handwheel 4| of the receiver selsyn in the proper direction to cause angular movement of the rotor of this selsyn or phase shifter equal to that through which the rotor of the transmitter selsyn I1 has been turned by the transmitting operator,

thereby realigning the" phase position of the voltages across transformers 39 and I2, restoring the plate currents of tubes I3 and I3 to balance and bringing pointer 24 back to zero position, in which position the data indicated by pointer 26 on indicator card 25 of the receiver selsyn again corresponds to the data indicated by pointer 26 on indicator card 25 of the transmitter selsyn.

In the form of the invention shown in Figs. 3 and 4, the equipment at the receiver is arranged to provide for automatic follow-up, so that as the transmitting operator rotates the dial 25 of his transmitter selsyn H, the unbalanced voltages produced thereby in the de tector-modulator 42 (see Fig. 3) of the receiver are utilized to operate, through suitable amplifier or motor control means 43, a pair of relays in circuit with a reversible motor 66 that may be used to operate a pcnderable object, if

desired. Motor 66 has a repeat-back connection -to the rotor of receiver selsyn or phase shifter 20, whereby movement of the transmitter selsyn is automatically accompanied by a synchronous movement of the receiver selsyn 26, so that the data card reading of the receiver always corresponds to that of the transmitter.

Fig. 4 shows the wiring diagram of the system of Fig. 3. The transmitter in Fig. 4 is quite similar to that of Fig. 2, but is shown provided with a difierent type of selecting network l4. This network consists of a band pass filter arranged to admit to the frequency doubler input transformer 29' the timing line frequency only and to sharply reject the double frequency variable phase output of amplifier l8 as well as any other extraneous voltages which may be present. The frequency doubler I5 is shown as employing two half wave rectifiers 30 for obtaining full wave rectification.

The selecting network 6' of the receiver 2 is similar to the network H of the transmitter and serves to prevent the timing generator frequency supplied by leads 5 through transformer 45 from reaching the detector input-transformer 46, but readily passes the double frequency, variable phase' signal potential from the transmitter selsyn to transformer 46 for application to the rectifier tubes 41 and 41' of the detectormodulator 42. The receiver, detector circuit comprises the pair of half-wave rectifier tubes 41 and-41' supplied with a local comparison voltage 56' are at the same potential.

placement, and under this condition the voltages reaching rectifiers 41 and 41' are equal and the rectified voltage drops appearing across resistors 49 and 49' are equal and opposite, whereby the outer terminals of resistors 53 and 53' in the cathode-grid circuits of modulator tubes 50 and Tubes 50 and 50' are supplied with a low frequency voltage, such as a 60 cycle voltage, by way of leads 5| and transformer 52. As the incoming signal potential is shifted in phase, resulting in the unbalancing of the outputs of rectifiers 41 and 41, the gains of the

modulator tubes

56 and 56 are similarly unbalanced and the 60-cycle voltage from transformer 52 is amplified more readily by one of these tubes than by the other and a net Gil-cycle voltage reaches the transformer 54 in the output circuits of these tubes.

Transformer 54 passes this net 60-cycle voltage to the grids of relay operating tubes 55 and 55' of the motor control means '43 in 180 out of phase relation. These tubes are supplied with an A. C. plate voltage by leads 56 connected to -cycle supply leads 5| and hence the net voltage passing through transformer 54, resultof motor 66. Motor 66 rotates in the proper direction to move the datacard- 25 of the receiver selsyn into synchronism with the correspond ing card of the transmitter selsyn and where a ponderable controlled object 58 is driven from motor 66,, such object is moved into synchronism with the transmitter selsyn, the repeat-back connection between motor 66 and the rotor of the repeater selsyn serving to re-establish the phase relationship of the signal and local comparison voltages, thereby deenergizing the energized relay 51 or 51' and stopping the motor 66 with the receiver indicating means 25, 26 in correspondence with the corresponding transmitting means 25, 26.

The operation of motor 66 will be apparent when it is noted that the motor field winding 59 is permanently connected across the supply leads 60 and that the positive lead .60 feeds two equal resistances 6| and 6| thatare adapted to be connected through normally closed relays 51 and 51', respectively, to the negative supply lead 66, the ends of each of the resistances 6| and 6| I being'connected to opposite brushes of the armadeenergization of the energized relay 51 or 51',.

as the case may be, such relay closesso that the armature of motor 66 is short circuited through relays 51 and 51' in a full strength field resulting in very strong dynamic braking and the immediate stoppage of the motor. In order to further insure against over-shooting and hunting of motor 66 about the position of synchronous alignment, resistors 63 and 63' are shown respectively connected to opposite brushes of motor 66 and are also connected to resistors 64 and 64 that are interposed between the two halves of the secondary winding of transformer 54. Changes in speed of the motor 66 corresponding to acceleration and deceleration of this motor produce variations in the back E. M. F. of this motor, which variations are applied to the grids of tubes 55 and 65' by virtue of the potential drops in resistors 64 and 64', the connections being such that the voltage produced across the armature of motor 66 acts on tubes 55 and 55' in a direction to cut the plate current of the driving tube 56 or 55', as the case may be, to zero before the phase shifter or receiver "selsyn 20 is fully restored to synchronism, whereby motor 66 is brought to restin a dead beat manner and without over-shooting or hunting.

When it is desired to transmit two or more channels of data over the same pair of transmission leads simultaneously, the somewhat modified system of Figs. 5 and 6 may be used. This system employs the same principles employed in connection with the preceding figures except thatan additional high frequency is generated andvaried in phase for each new channel desired. This necessitates the use of somewhat more complicated selecting networks at the transmitter and receiver stations in order to properly separate the various frequencies.

Referring to Fig. 5, the receiving station is provided with a synchronous multiple frequency generator 6] arranged to generate a fundamental frequency and additional higher frequencies, l. e., one for each channel desired. For multiple channel operation, it is preferable to have these higher frequencies bear no harmonic relation to each other in order to avoid inter-channel interference due to unwanted higher harmonics from either the timing or channel frequencies. The timing frequency produced by generator 61 is fed to the transmission line through the selecting network 68. At the transmitting station a selecting network 69 comprising a band pass filter passes this line frequency to transmitters '10 and H, marked on Fig. 5 as A and B. Each of these transmitters 10 and H is similar to the single channel transmitter described in connection with Figs. 1 to 4, but is suitably modified to produce an output frequency suitable for its individual channel of operation. These output frequencies are fed through

leads

12 and 13, respectively, to selecting network 69 and returned through line 1 to selecting network 68 atthe receiving station. Selecting network 68 comprises two band pass filters, one of which passes the frequency corresponding to the output of transmitter 10 to the receiver 15, in whichit is compared with a similar frequency from a suitable receiver "selsyn or. phase shifter fed from synchronous generator 61. In a similar manner, the frequency corresponding to the output of transmitter H is fed "through the other band pass filter of network 68 to receiver 11, where it is compared, as before, to a similar frequency supplied from generator 61. Additional channels may be added, if desired, by the addition of other filters and additional generating apparatus to supply the local station comparison voltages.

Referring now to Fig. 6, showing a wiring diaage supplied from generator 61 (not shown in Fig. 6), is fed through leads 19 and transformer 19 to line' I, this timing frequency voltage being prevented from reaching the receiving circuits by the action of the band pass filters 14 and 16 of the selecting network 68. At the transmitting end, this timing frequency voltage is selected by the filter 19 of the selecting network 69 and passed to the frequency doubler and through condenser 8I to transformer 82, through single phase to three-phase network 83, phase shifter or transmitter selsyn 84, amplifier and transformer 86 back over line 1 to the receiving station. At the receiving station this signal voltage of double timing frequency, such as 660 cycles, and variable phase is selected by filter 16 and passed through transformer 86 to detector tubes 81 and 81' and compared with a locally generated A. C. supply (such as a 660 cycle supply) by observation of meter 90 and operation of receiver "selsyn" or phase shifter 9| by turning handwheel 92. Receiving dial 25 is thus brought into synchronous alignment with trainsmitting dial 25.

The operation of the second data transmitting channel is similar, in that at the transmitting end the timing frequency voltage, such as 330 cycles, selected by filter 19' of network 69 and doubled by frequency doubler 80, passes through condenser 8| to transformer 93 having its primary winding connected to the terminal of the secondary winding of transformer 94. Hence, the double frequency voltage output of doubler 80 has added in series with it in transformer 93 the voltage appearing across one-half of the secondary winding of transformer 94. Thus, when using a 330 cycle timing frequency, the voltage reaching the grid of tube 95 is composed of 660 cycles plus 330 cycles. Tube 95 is biased as a modulator and hence its output circuit provides voltages of frequencies consisting of the sum and difference of frequencies of the voltages of its grid circuits. Thus, in the above example, one of these components is 330 plus 660, or 990 cycles. This frequency is selected by filter 96 and passed through transformer 91, single phase to threephase network 98, transmitter "selsyn or phase shifter 99, amplifier I00 and transformer IOI to line 1. At the receiving station this signal frequency (i. e., for example 990 cycles) of the second or B channel is selected by filter 16 and passed through transformer I02 to detector tubes I 04 and I04 and is compared with a locally gen erated similar frequency (990 cycles in the'example chosen) by the previously described means involving the zero center meter I05 and receiver phase shifter or "se1syn I06, whereby the receiver "

selsyn indicator

25, 26 is brought into synchronism with the

transmitter selsyn indicator

25, 26.

Although the system of Figs. 5 and 6, for the sake of simplicity, is shown as providing for twochannel transmission, it is to be understood that additional channels maybe added, as desired, through the use of additional transmitting and receiving apparatus including proper filters. Thus, in Fig. 5, additional leads are shown for leading to apparatus for another channel.

The novel data transmission system of this invention thus provides one or more channels of data transmission over a single pair of leads, and if these leads are telephone wires, the operation of the data transmitting system will not interfere with voice transmission over the same wires so long as suitable filters are used in'the telephone apparatus to exclude data transmission frequencies.

The positional control of ponderable objects, as disclosed in connection with Figs. 3 and 4, is equally applicable to the multi-channel system of Figs. 5 and 6.

In all forms of the invention, the transmitter apparatus is light and compact and can be readily carried from place to place by one man.

As many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

.1. A data transmission and control system comprising a transmitter, a receiver, a two-wire ance with said phase position, and means for so operating said indicator.

2. In a/control system of the character described, atwo-wire transmission line, means for supplyin said line with an alternating potential of funda ental frequency, a transmitting station connected to said line and having means for converting said alternating potential to one of different frequency, a receiving station connected to said line remote from said transmitting station, controlling means including a variable phase transmitter at said transmitting station for utilizing said different frequency potential to deliver electric signal impulses of changing phase to said line in accordance with data to be transmitted to said receiving station, means at the latter station for detecting the phase position of said signal impulses, and controlled means at said receiving station adapted .to be operated in accordance with the output of said detecting means in synchronism with said controlling means.

3. In a control system of the character described, a two-wire transmission line, a transsaid variable phase potential. and means for using said potential in operating a controlled member.

4. In a data transmission and control system, a two-wire transmission line, a receiver, a power 7 supply at said receiver connected for supplyingv a fundamental frequency potential to said line, a

transmitter having means including a frequency changer for changing said potential to one of different frequency together with-a transmitter phase shifter for varying the phase position of said different frequency potential in accordance with variations in the data transmitted, said variable phase different frequency potential being delivered to said line for transmission to said receiver, said receiver having a receiver phase shifter energized from said power supply and cooperating means for. detecting the phase position of said variable phase potential, and means cooperable with said detecting means for visually indicating said variations in the data transmitted.

5. A system of the character described com-- prising a two-wire transmission line, a receiver comprising a multiple frequency generator, a selecting network connected to said generator and said line and serving to direct a single phase fundamental frequency potential from said generator onto said line, a transmitter comprising a frequency doubler, a selecting network for receiving said single phase potential and for delivering the same to said doubler to be doubled in frequency, a transmitter selsyn havmitting station connected to said line, a receiving station connected to said line remote from said transmitting station, means at said receiving station for supplying a fundamental frequency potential to said line, a selecting network at said receiving station for delivering said potential to said line, a selecting network at said transmitting station for "receiving said potential, means at said transmitting station for changing said potential to one of different frequency and for shifting the phase thereof in accordance with data to be transmitted, said transmitter selecting network acting to "deliver said variable phase different frequency potentialto said line for transmission to said receiving station, and

, said receiver selecting network acting-to select ing three phase and single phase windings, a network for converting the double frequency single phase potential to a three phase potential for supplying the three phase winding of said selsyn," an amplifier connected to the single phase winding of said selsyn and to said line for delivering an amplified version of the variable phase double frequency signal output of said selsyn to said line for transmission to said receiver, a receiver selsyn at said receiver supplied with double frequency three phase potential from said generator, said receiver having a detector supplied with a double fundamental frequency comparison voltage fromsaid receiver selsyn, a meter controlled by said detector, said receiver selecting network serving 'to direct said variable phase double frequency signal potential to said detector, whereby variations of the relative angular positions of said transmitter and receiver.selsyns cause said detector to operate said meter from zero position.

6. In a positional control system of the character described, a two-wire transmission line,'a transmitter comprising a transmitter selsyn for supplying a variable phase signal potential to said line, a receiver comprising a receiver selsyn, a thermionic phase position detector connected to said line for receiving said signal potential, and a meter controlled from said detector, said receiver selsyn being connected to said detector for supplying a comparison potential thereto, whereby relative movement of said transmitter and receiver selsyns serves to effect operation of said meter to indicate such relative movement.

'7. In a variable phase data transmission and I control system for multiple channel transmission, a two-wire transmission line, a transmitting stasaid transmitters varying in accordance with the data transmitted; and a receiving station having a plurality of receivers including phase detecting said line from said transmitter to said receiver for transmitting intelligence and means for also supplying a fundamental frequency voltage over said line from said receiver to said transmitter for use in energizing said variable phase potential supplying means.

9. A data transmission and control system comprising a transmitter station and a remotely located receiver station, a two-wire transmission line extending between the stations, means at the receiver station for supplying the line with A. 0. potential of a predetermined substantially fixed frequency, means at the transmitting station for superposing upon the line a potential of a frequency difl'ering fromthe fundamental frequency and in any desired phase position, and means at the receiver station proportionally responsive to any shift of the superposed phase position. a

10. A data transmission and control system comprising a transmitter and a remotely located receiver, said system comprising a two-conductor transmission line as the only conducting means interconnecting said transmitter and receiver, said transmitter having means for delivering a variable phase signal potential that is variable without limit and corresponding to the data transmitted to said line for transmission to said two-conductor transmission system serving as the only conducting means interconnecting said transmitter and receiver and transmitting said signal impulses to the latter.

12. In a control system of the character described, a two-conductor transmission line, a variable phase transmitter having a controlling member and arranged for delivering electric signal impulses of changing phase to said line, said signal impulses being variable without limit as to phase in accordance with the position of said controlling member, a variable phase receiver connected to said line for receiving said signal impulses, and a controlled member located at said receiver, said receiver having means for detecting the phase position of said signal impulses and for operating said controlled member in response thereto, whereby said controlled member is moved synchronously with said controlling member, said two-conductor transmission line constituting the only electrical connection between said transmiter and receiver.

ERIC J. ISBISTER. FRANCIS L. MOSELEY.