US2394044A - Control system - Google Patents

Description

Patented Feb. 5, 1946 UNITED STATES PATENT OFFICE CONTROL SYSTEM Application December 22, 1944, Serial No. 569,354

Claims.

Our invention relates, generally, to control systems, and it has referenc in particular to carrler communication and supervisory control systems for a plurality of stations.

Generally stated, it is an object of our invention to provide an improved carrier communication and supervisory control system that is simple and inexpensive to manufacture and is emcient and easy to operate.

More specifically, it is an object of our invention to provide for effecting supervisory control of, and telephone communication with, a plurality of remote stations from a central dispatching oflice over a common carrier channel.

It is also an object of our invention to provid indications of apparatus at remote stations be-' cause of interference between communication equipment and supervisory control equipment operating over a common channel.

Yet another object of our invention is to provide for operating supervisory and control equipment of a plurality of remote stations and of a central dispatching ofilce in combination with a arc-frequency duplex carrier communication sys- An important object of our invention is to provide for interrupting the communication and bellringing circuits of the telephone equipment as soon as a supervisory or control function is commenced, and to prevent interruption of a communication by initiation of supervisory or control functions.

A further object of our invention is to provide for synchronizing the operation or the supervisory control line relays at a plurality of remote stations in a multi-station system, wherein the dispatching omce and remote stations operate on different carrier frequencies,

Still another object of our invention is to provide for combining a multi-station supervisory control system with a two-frequency duplex carrler communication system so as to require only a single carrier transmitter and receiver at the dispatching omce and at each station.

Other objects will in part be obvious, and will in part be described hereinafter.

In accordance with our invention, both telephone communication with, and supervisory control of a plurality of remote stations are effected from a central dis atching oiiice over a common carrier channel. The dispatching office transmits on a carrier frequency F1 which is received by all of the stations. whereas the stations transmit on a carrier frequency F2 which is received only by the dispatching ofllce. The supervisory start relays at both the remote stations and the dispatchin omce interrupt their respective telephone circuits to prevent interference with supervisory or control operations. Prevention of supervisory or control interference with the telephone system is prevented by using the receiving relays at the remote stations and the central dispatching omce to interrupt the operating circuits for their respective supervisory start relays in response to the energization of the carrier transmitters at the dispatching ofiice and remote stations, respectively, whenever a telephone communication is being effected.

For a more complete understanding of the nature and scope of our invention, reference may be made to the following detailed description which may be studied in connection with the accompanying drawings, in which:

Figure l is a diagrammatic view of the apparatus and circuit connections at the central dispatching oilice of a two-frequency duplex com munication and supervisory control carrier sys tem embodying the invention in one of its forms; and

Fig. 2 is a diagrammatic view of the apparatus and circuit connections at any one of a number of remote stations in a two-frequency duplex com munication and supervisory control carrier system embodying the invention in one of its forms.

Referring to Fig. 1, it may be seen that the communication equipment It) above the dot-dash line at the dispatching office may comprise, generally, a hand-set H which may be connected in conjunction with a telephone bell I2 and suitable ringing means such as the hand generator I3 to any pair of the conductors M of a transmission line or the like, through a hybrid coil iii of a type well known in the art, an audio amplifier l6 and a carrier frequency transmitter l1 operating on a frequency F1, by means of a coupling circuit including coupling condensers l8 and inductances I9 for effecting telephone communication over the conductors. In addition,

the telephone equipment may include a carrier receiver 20 operating on a frequency F2, which may be connected to the hand-set l I through the hybrid coil l5 by means of conductors 2| and 22, and also connected to the transmission conductors it through the coupling condensers l8 and inductances I9. Means such as a calling relay 23 which responds to the frequency of the generator l3 may be provided for applying a ringing voltage to the carrier transmitter from a source 24. Code bell detector apparatus 25, which may be of any type well known in the art of carrier telephony, may be provided for operating a voice relay 26 in response to an incoming telephone communication, for keeping the carrier transmitter l1 energized thru contact members 26a,

and a code bell detector relay 28 which responds to the receipt of a ringing voltage of a predetermined frequency received by the carrier receiver. An additional source of local ringing voltage 29 may be provided for ringing the bell I2 in response to the receipt of ringing impulses by the code bell detector apparatus 25.

Referring to Fig. 2, it may be seen that the telephone equipment 30 shown above the dotdash line, and which is typical of the equipment at each of the remote stations, may comprise a hand-set 3|, which may be connected in conjunction with a telephone bell 32 and source of ringing voltage such as the hand generator 33 through a hybrid coil 35 and an audio amplifier 38- to a carrier transmitter 31, which may operate on a frequency F2, and be connected to the transmission conductors M at some remote location by coupling'condensers l8 and inductances I9 in a similar manner as is the telephone equipment at the dispatching office. In a like manner the hand-set 3| at the remote station may be connected through the hybrid coil to a carrier receiver 40 at the remote station, which operates on a carrier frequency F1 transmitted by the carrier transmitter I! at the dispatching ofi'ice. The telephone equipment at the remote station may also include code bell detector apparatus 45 of any type well known in the art for operating a voice responsive relay 46 in response toan incoming telephone communication, and code bell detector relay 48 responds to the frequency of the ringing voltage from the dispatching ofii-ce; A calling relay 4'! may be provided for connecting a source 44 of ringing voltage to the transmitter in response to receipt of ringing signals from the hand generator 33. An additional source 49 may be provided for ringing the bell 33 in response to ringing signals from the dispatching office. The reference numeral 50 may denote, generally, the complete telephone and supervision equipment at any of a number of other substations, which may be similar in every respect to that shown and described in connection with the equipment 30 of the one substation to which the explanation will be directed.

In order to provide for combining with the carrier communication equipment of the dispatching ofiice and remote stations, supervisory control equipment for controlling and supervising the operating condition of apparatus such as circuit breakers and the like at any of the remote stations, we have combined with the telephone equipment supervisory control equipment shown below the dot-dash lines and denoted generally by the numerals and 52 respectively. The supervisory equipment may be of the multi-station type such as is described in detail in Patent No. 2,059,204, which issued on November 3, 1936 to H. P. Boswau. In order to facilitate an explanation of our invention without unnecessarily involving the situation by a detailed description of the many connections and operating relations of the various relays shown and described in detail in the Boswau patent hereinbefore referred to, we have represented the bulk of the supervisory control equipment by means of the boxes 53 and 54 at the central dispatching office and remote station respectively. All of the apparatus represented by these boxes is substantially identical in arrangement and operation with the bulk of the apparatus shown and described in the Boswau patent. Where any changes have been made in the circuits and connections, the particular relays concerned in the present invention have been shown outside of the boxes, and the changes in circuits have been shown and the manner of operation will be described in detail hereinafter. Thus the invention may be clearly defined and explained without confusing the issue by means of a plurality of sets of drawings showing old and well-known apparatus in connection with the invention, as well as by lengthy and detailed explanations of the operation of such well-known apparatus which may detract from the value of the actual invention.

In order to provide for operating supervisory control equipment particularly of the multi-station type shown and described in the Boswau patent, over the channel of a carrier communication system such as that hereinbefore described, provision may be made at the dispatching oflice for operating a tone transmitter 55 to superimpose tone impulses on the carrier frequency transmitter I"! for controlling and supervising the operation of equipment at the remote stations. For example, the tone transmitter 55 may be controlled by using armature 56 and front contact 51 of the dispatching ofiice impulsing supervisory control relay 430 to energize the tone transmitter to produce impulse signals in response to the operation of the dispatching office selecting, controlling and supervisory equipment. Thus instead of energizing and deenergizing conductors such as the line conductors 432 and 433 of the Boswau patent by connecting them to and disconnecting them from a source of direct current as described in the Boswau patent, tone impulses are superimposed on the dispatching olfice carrier frequency and transmitted over'the conductors 14 by means of the im ulsing relay 430 for operating the supervisory control equipment at a remote station. 1

The supervisory equipment at the dispatching oflice may be further modified from that shown and described in the Boswau patent by providing a tone receiver 59 which may be connected to the carrier receiver 20 by means of conductors 2| and 22 for operating the line supervisory control relay 43! in response to the receipt of tone impulses on the carrier frequency F2 from any of the remote stations. Thus instead of operating due to receipt of direct current impulses over line conductors 432 and 433 as in the Boswau patent, the line relay 43! operates due to tone impulses from the remote stations. Tone blocking filters 60 may be provided for preventing pass ge of any voice frequencies which might operate the supervisory equipment.

In a like manner the supervisory control equipment 52 at the remote stations may be modified by utilizing the impulsr'ng relay 5H1 to operate a tone transmitter 62 for superimposing tone impulses on the carrier transmitter 31 in response to the operation of the substation selecting, controlling and supervisory equipment. A tone receiver 63 may be provided for operating the sub,- station line relay 5 in response to impulse signals received from the dispatching ofilce through the remote station carrier receiver 43. Tune blocking filters 60 may be used to prevent false operation of the supervisory equipment by voice frequencies. 7

In order to prevent interference between the communication and supervisory control equipment, these equipments may be interlocked so that only one or'the other may operate at one time. For example, referring to Fig. 1 it may be seen that at the central dispatching ofiice ringing and telephone communication circuits extend from the hand-set H and generator l3 through the armature 64 and back contact 66 of the receiving start supervisory control relay 4", armature 68 and back contact '6! of the sending start supervisory control relay 404, back contact 10 and armature H of the line relay 43l, as well as back contacts 28!: of the code bell detector relay before reaching the hybrid coil I 5. Accordingly, operation of the telephone communication system is impossible while the supervisory control equipment is either receiving or sending, since one or more of these contact will be opened.

For the purpose of preventing interference of the supervisory control equipment with a telephone communication, means may be provided at the dispatching oflice for preventing the operation of the supervisory control equipment durin a telephone communication. For example, a receiving relay 13 may be provided which operates whenever the carrier receiver 20 receives the remote station carrier frequency Fa, by interposing contact members 13b of the receiving relay in the energizing circuit for the sending start supervisor control relay 404. Operation of the start relay 444 may be prevented so long as the receiving relay I3 is in the energized position due to the receipt of a telephone communication on the carrier frequency F2 from one of the remote stations. The dispatching oflice is thus prevented from starting a supervisory or control operation after the carrier frequency has been transmitted from a remote station, though it is not prevented from receiving.

Referring to Fig. 2, it may be seen that the operation of the telephone equipment at any one of the remote stations during a supervisory control operation may be prevented by interrupting the telephone circuit through any one or all of armature l4 and back contact I5 of the receiving start supervisory control relay 5I4, armature l6 and back contact 11 of the sending start supervisory control relay 516, or armature Hi and back contact 18 of the line relay 5W, as well as by contact members 48b of the code bell detector relay 48. Interference of the supervisory control equipment with telephone communications may be prevented by interposing contact members 800. of a receiving relay 80 associated with the carrier receiver 4. in the energizing circuit for the opcrating winding of the sending start supervisory control relay 5i'6. Since the receiving relay 80 is energized in response to receipt of the carrier frequency F1 from the dispatching oilice, it re mains in the energized position during a telephone communication and prevents initiation of a supervisory control operation from the remote station.

Whenever communication is initiated from a remote station, the operator applies ringing voltage to his telephone extension line by turning the crank of the magneto-type generator 33. With the supervisory control equipment in a deenergized condition, the ringing potential is applied to the calling relay 41 through the hybrid coil 35 by means of a circuit extending from the generator 33 through conductor 8|, and through conductor 82, armature 14, back contact I5, conductor 83, armature 16, back contact 11, conductor 85, armature 18, back contact 19, conductor 86 through contact members 48b of the code bell detector relay to the hybrid coil 35. The calling relay 41', which is sensitive to the frequency of the ringing voltage, operates, closing contact members 41a which start the carrier transmitter 31 operating on a carrier frequency F2. At the same time, contact members 41b close connecting the source of ringing-out voltage 44 to the input terminals of the carrier transmitter so as to modulate the output of the transmitter and transmit a ringing signal.

Reception of the carrier frequency F: by the carrier receiver 24 at the dispatching oiiice operates the receiving relay 13. Contact members 13b open, interrupting the energizing circuit for the sending start supervisory control relay 404 so as to prevent the dispatching ofllce supervisory control equipment from sending. At the same time, contact members 13a close, completin an energizing circuit for the carrier transmitter ll which transmits a carrier frequency F1 over the transmission conductors H. The code bell detector relay 28 operates in response to the ringing signal and connects a local source of ringing voltage 29 to the bell i2 through contact members 28a and the interlocking circuit of the supervisory relay back contacts. Ringing by the dispatcher is prevented by reason of contact members 28b being open.

The reception at all of the remote stations, in cluding the remote station which is initiating a communication, of the carrier frequency F1, operates all of the receiving relays at the remote stations. The energizing circuits for the sending start supervisory control relays M6 at the remote stations are thereby opened at contact members 80a, preventing the supervisory equipment at all of the remote stations from sending during a telephone communication. While a conversation is maintained, the voice relay 26 at the dispatching omce maintains an energizing circuit for the carrier transmitter F1 through contact members 26a, while the voice relay 46 likewise maintains an energizing circuit for the carrier transmitter 31 through contact members 46a until the conversation is completed. When conversation is completed, the voice relays at both stations open deenergizing the carrier transmitters. The receiver relays 13 and 80 are thus deenergized, removing the interlocking with the supervisory equipment.

Communication may be initiated from the central dispatching ollice by the operator cranking the hand generator l3 to apply ringing voltage to his telephone extension. The ringing voltage is applied to the calling relay 23 through the hybrid coil 15 and an interlocking circuit extending from the generator through conductor 81 on one side, and through conductor 88, armature 65 and front contact 66 of the receiving start relay 402, armature 68 and back contact 69 of the sending start relay 404, back contact 10 and armature II of the line relay I, and back contact members 28b of the code bell detector relay to the hybrid coil IS on the other side. The calling relay 23 operates, providing an energizing circuit for the carrier transmitter il through contact members 23a, and connecting the source of ringing voltage 24 to the audio input terminals of the carrier transmitter through contact members 23b to transmit a ringing signal.

The reception of carrier frequency F1 at all remote stations operates the remote station receiving relays 8B, which interrupt the energizing circuits for the sending start supervisory control relays 516, thus preventing the supervisory control equipment at all of these stations from sending. The ringing voltage applied to the dispatching oiiicer carrier frequency operates the code bell detector relays 48, which connect thelocal sources of ringing voltage 49 to the bells 32 through contacts 48a and the interlocking supervisory relay by the carrier receiver 20, the receiving relay 13 at the dispatching oflice operates. Contact members 13b open interrupting the energizing circuit for the sending start relay 494, and prevent the supervisory equipment at the dispatching office from sending during telephone communication.

It will be noted that during the time interval between the commencement of a communication from the dispatching office and the answering of the attendant at the called station, there is nothing to prevent a supervisory operation being commenced from the dispatching oiiice, since the remote stations are never prevented from receiving 1 a supervisory or control signal. Thus, in the event that the telephone extension at the dispatching office is being operated by someone other than the dispatcher, any supervisory operation which the dispatcher may initiate during this interval will take precedence over the telephone communication.

When any automatic operation takes place at a remote station, the supervisory start relay 5l6 at the particular remote station is energized through a supervisory control circuit which includes the normally closed contact members 80a of the remote station carrier receiver receiving relay 80. As soon as the start relay 5I6 operates, it provides a holding circuit through armature 546 and other of the control apparatus enclosed Within the boxes so that it is maintained in the operated position independently of the remote station receiving relay 8!]. Operation of the sending start relay 5I5 energizes the sendin drive relay 591 through a circuit contained within the boxed portion of the supervisory control equipment. Operation of the sending drive relay starts the transmission of the remote station carrie frequency F2 since the carrier transmitter 31 is started through armature 90 and front contact 9I of the sending drive relay 501. The telephone circuit is interrupted by the sending start relay 5I6 by the separation of the armature I6 from back contact 11, thus preventing operation of the telephone equipment during a supervisory operation.

Impulsing relay 5Ill is subsequently operated by the substation selecting, controlling and supervisory equ pment, and energizes the tone transmitter 52 through armature 89 and front contact 99 to modulate the carrier frequency F2 with coded tone impulses.

At the dispatching oflice reception of the tone impulses on the carrier frequency F2 energizes the line relay 43! which operate the supervisory selecting and controlling equipment by providin a connection to indirect positive through armature 45I in a similar manner to that described in the Boswau patent hereinbefore referred to. At the same time, the line relay 43I connects the output of the carrier receiver 29 directly to the audio input terminals of the carrier input transmitter I! through conductors 92, and conductor 2|, conductor 93, front contact 95, armature 96, conductor I03, conductor 91 and conductor 98.

The transmitter I'I retransmits the tone impulses received from the initiating remote station to all remote stations on the carrie frequency F1. Reception of the tone impulses at all of the remote stations on carrier frequency F1 energizes the line relays 5 which are responsive only to tone signals on carrier frequency F1, and opens the energizing circuits of the impulsing relays 5I0 to terminate the first impulse. In the system of the Boswau patent the remote station line relay are picked up directly due to energization of the line conductors by the impulsing relay.

As is common in supervisory control systems, the number of impulses sent from the initiating station depends on the point number on the supervisory system of the device which initiated the operation. At each remote station other than that which initiated the particula operation, the operation of the line relay 5 opens the telephone circuit and energizes the receiving start relay 5 through circuits which extend through portions of the supervisory control equipment shown in the box portion, and which are identical with the corresponding circuits shown in the Boswau patent. The operation of relay 5M prevents the supervisory start relay 5I5 from bein energized. This prevents the supervisory equipment at all these stations from sending. At the completion of the first group of impulses from the initiate remote station, all of these stations are completely locked out in a manner which is clearly described in connection with the description in the Boswau patent.

Resetting of the supervisory control equipment at the end of a supervisory control operation may be effected by providing auxiliary front contact I90 and armature IDI on the impulse relay 439 at the dispatching oifice where the resetting operation originates. This contact serves to maintain the dispatching station carrier transmitter energized until the end of the resetting impulse, which is provided in the usual manner as described in the Boswau patent. This auxiliary contact provides for maintaining the dispatching ofiice carrier frequency as the contacts of the sending start relay 5I6 open.

In affecting a supervisory operation from the dispatching station, the operation of any supervisory point selection key at the dispatching oflice affects energization of the sending start supervisory control relay 404 through a circuit which extends through back contacts 131) of the receiving relay and other contacts in the supervisory control equipment as described in the Boswau patent. The carrier transmitter I! is energized through contact members 13a, putting the carrier frequency F1 on the line. Reception of this carrier frequency at all of the remote stations operates the remote station receiving relays 80 which interrupt the energizing circuits for the remote station sending start relays 516, thus preventing any of the remote stations from sending supervisory signals. Interference of the telephone system with the supervisory control system is prevented through the opening of contact member 69 of the sending start relay 404 which is connected in the telephone circuit. At th same time, the carrier receiver 20 and the tone receiver 59 are connected to the audio input terminals of the carrier transmitter through armature I98 and front contact I09 of the sending start relay 494, which makes it possible for the tone receiver at the dispatching oflice to receive the local tone transmitter.

Subsequent to the energization of the start relay 404, the impulsing relay 430 is energized connecting the tone transmitter 55 to the audio input terminals of the carrier transmitter H. The impulsing relay 8 is operated in accordance with the operation of the dispatching office selecting. controlling and supervisory equipment in a manner similar to that described in connection with the Boswau patent.

Upon receipt of the modulated carrier frequency F1 at all of the remote stations, the line relays ill at all of these stations are operated through the tone receivers 63. Operation of the line relays opens the telephone circuits at each of the stations through armature 18 and back contact 19, and these circuits are held open by the subsequent energization of the receiving start relays 5, which are energized before the deenergization of the line relays 43!. At the end of the first group of impulses from the dispatching oflice, the station relay at the selected station only is energimd, and the supervisory system at all of the other remote stations is locked out until the resetting signal is sent in accordance with the description thereof provided in the Boswau patent. Carrier at the selected station may be maintained by one of the supervisory relays such as the sending drive relay 501, through armature 90 and front contact 9|.

From the above description and the accompanying drawings, it will be apparent that we have provided in a simple and effective manner for combining a supervisory system of the multistation type with a two-frequency duplex carrier communication system. Only a minimum of additional equipment is required since both the telephone equipment and the supervisory equipment utilize the same carrier transmitters and receivers. Positive synchronizing on the remote station supervisory equipment is eflected under all operating conditions, thus readily permitting station selection in the manner described in the Boswau patent.

Since certain changes may be made in the above-described construction, and different embodiments may be provided without departing from the spirit and scope thereof, it is intended -that all the matter contained in the above description and shown in the accompanying drawings be considered as illustrative and not in 9, lim. iting sense.

We claim as our invention:

1. In a communication and control system for a dispatching oflice and a plurality of remote stations having a single carrier channel, means at the oflice and stations including telephone communication equipment and circuits for transmitting telephone communication signals between the ofiice and stations over the carrier channel, supervisory control means at the oilice and stations including tonetransmitters and receivers operating over the carrier channel, means responsive to the initiation of a supervisory or control operation from the office or any of the stations for interrupting the telephone communication circuits, and means responsive to the transmission of a telephone communication signal for preventing operation of the supervisory control means during a telephone communication.

2. The combination in a multi-station supervisory control and communication system for a dispatching office and a plurality of stations having a common carrier channel, of supervisory control equipment of the multi-station type including carrier transmitters and receivers for controlling and supervising the operation of appa' ratus at the stations over the common channel, telephone equipment for communicating between the office and stations over the common channel through the same transmitters and receivers as the supervisory control equipment, circuit means responsive to the operation of the supervisory control equipment for preventing operation of the telephone equipment, and means responsive to the initiating of a telephone communication from one of the stations for preventing the oilice supervision equipment from starting.

3. In a communication and supervisory control system for an ofilce and a plurality of remote stations having a single carrier channel, a car rier transmitter at the ofllce operating over the channel on one frequency, a carrier transmitter at each of the stations operating over the channel on another frequency, telephone equipment at the station and offices operating over the carrier channel including a receiver at the ofifice responsive to the station carrier and receivers at the stations responsive only to the oflice carrier, supervisory control equipment of the multistation type at the ofiice and stations including tone transmitters controlled by the supervisory equipment for transmitting coded impulses on the ofiice and station carrier frequencies respectively, and means for retransmitting a tone transmitted by a remote station on the ofiice carrier to synchronize the other remote stations with the sending station.

4. In a supervisory, control and communication system for a dispatching office and a plurality of remote stations having a common communication supervisory and control channel, a carrier transmitter at the oiiice operating over the channel on one frequency, a carrier receiver at each station for receiving on the ofiice carrier frequency, a carrier transmitter at each oilice operating over the channel on another frequency, a carrier receiver at the oifice for receiving on said another carrier frequency, telephone equipment at each station including a calling relay responsive to ringing at said station for operating the carrier transmitter at said station to call the dispatching ofiice, supervisory control equipment at the dispatching ofn'ce and stations including tone transmitters controlled by supervisory drive relays for effecting supervisory control functions over the channel, and means including a receiving relay associated with each of the station carrier receivers responsive to the dispatching office carrier frequency and a receiving relay associated with the office carrier receiver responsive to the station carrier frequency for preventing operation of the supervisory control equipment during a telephone communication.

5. In a supervisory control and communication system for a dispatching oflice and a plurality of remote stations having a common communication and signal channel connecting them, a carrier transmitter at the office operating over the channel on one frequency, a carrier transmitter at each station operating over the channel on another frequency, supervisory control equipment at the ofllce and stations having tone transmitters for modulating the carriers to effect supervisory and control functions, telephone equipment at the oflice and stations associated with the transmitters for modulating said transmitters including calling relays responsive to a ringing operation for operating the associated transmitter, carrier receivers at the oflice and stations including receiving relays each responsive only to the carrier frequency of the other for preventing operation of the supervisory equipment, and circuit means responsive to the initiation of a supervisory or control operation for preventing operation of the telephone equipment.

' 6. A control and communication system for a dispatching ofiice and a plurality of stations connected by a transmission line comprising, a carrier transmitter of one frequency associated with the transmission line at the ofiice, a carrier transmitter of another frequency associated with the transmission line at each station, telephone equipment at the oflice including a receiver operating on the remote stationcarrier frequency and at the stations including receivers operating on the ofiice carrier frequency for communicating only between the oflice and stations, supervisory control equipment of the multi-station type at the office and each station including a tone transmitter controlled by an impulse sending relay for producing code impulses on a tone receiver for operating a line relay in response to code impulses, and means at the dispatching office responsive to the receipt of code impulses from a remote station for connecting the office tone receiver to the office carrier transmitter for retransmitting said impulses to synchronize the supervisory equipment at the other stations.

' '7. In a control and communication system for a plurality of remote stations and a dispatching office, a single communication and control channel connecting the oflice and stations, a carrier transmitter at the dispatching station operating at one carrier frequency, carrier receiving means at each of the stations responsive to said frequency, a carrier transmitter at each station operating at another carrier frequency, carrier receiving means at the office responsive to the station carrier frequency, telephone means at the ofiice and stations operating on the ofiice and station carrier frequencies, supervisory equipment of the multi-station type requiring synchronized operation at the office and stations operating over the office and station carrier frequencies, and means at the oflice responsive to the receipt of a supervisory signal on the station frequency for retransmitting said signal on the office carrier frequency to synchronize all of the station equipments.

- 8. The combination with a duplex communication system having a dispatching office with telephone equipment including a carrier transmitter transmitting on a carrier of one frequency and a carrier receiver receiving on a carrier of another frequency and a plurality of stations with telephone equipment including carrier receivers receiving on the office transmitting carrier frequency and carrier transmitters transmitting on the oflice receiving carrier frequency, of supervisory control apparatus at the oflice including a tone transmitter for operating to send supervisory control impulses on the ofiice carrier frequency and a tone receiver responsive to supervisory control impulses on a'station carrier frequency, supervisory control equipment of the multi-station type at each station including a tone receiver to receive supervisory code impulses operating on the office carrier frequency and a tone transmitter for transmitting code impulses on the station carrier frequency, and means associated with the ofiice supervisory equipment for connecting the oifice carrier receiver to the ofiice parri'er transmitter for retransmitting code impulses from a sending station on the ofiice carrier frequency for synchronizing the supervisory equipment at the other stations with the supervisory equipment'of the sending station. a

9. For use with a duplex carrier communication system having a dispatching ofilce provided with telephone equipment transmitting over a common channel through a carrier transmitter,

of one frequency and receiving on a difierent frequency, and a plurality of remote stations provided with telephone equipment for transmitting over the common channel with the dispatching ofiice on said different frequency and receiving station carrier transmitter and a tone receiver for operating a long relay in response to impulses Z transmitted by the dispatching ofiice, means responsive to operation of the supervisory equipment at either the oflice or stations for rendering the telephone equipment at said location inoper- .-ative, and circuit means including a receiving ,relay at the ofiice and station responsive respectively to the station and ofiice carrier frequencies for preventing operation of the supervisory equipment during a telephone communication.

10. A communication and control system for a dispatching ofiice and a plurality of remote stations having a common communication and supervisory control channel comprising, telephone equipment at the ofiice including a carrier transmitter operating over the channel at one frequency, a carrier receiver operating over the channel on another frequency and having a callin relay responsive to receipt of a carrier of said other frequency, means including a calling relay and a source of ringing voltage at the office and each station for operating the associated office or station carrier transmitter to effect a communication with one of the stations or with the ofiice, supervisory control equipment at the oflice including a tone transmitter operated by an impulse relay for sending impulse signals over the ,ofiice carrier and a tone receiver operated from the office carrier receiver for controlling a supervisory control line relay, supervisory control equipment at each station of the multistation type including a tone transmitter operated by an impulse relay for transmitting impulse signals over the station carrier transmitter and a tone receiver operated from the station carrier receiver for operating a supervisory control line relay, circuit means at the ofiice and stations including contact members of the receiving relay for preventing operation of the supervisory control equipment at the oifice or station to transmit impulse signals during a telephone communication, and additional circuit means including contact members of the supervisory line relays at the oflice and stations for preventing operation of the telephone equipment during a supervisory or control operation.

WILLARD A. DERR. ROBERT C. CHEEK.

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