Title:
Supervisory control and telemetering system
United States Patent 2327251


Abstract:
My invention relates, generally, to supervisory control and remote metering systems and, more particularly, to systems for performing both supervisory and telemetering functions over a single communication channel. Heretofore telemetering and supervisory control functions have had to be performed...



Inventors:
Derr, Willard A.
Application Number:
US40445241A
Publication Date:
08/17/1943
Filing Date:
07/29/1941
Assignee:
WESTINGHOUSE ELECTRIC & MFG CO
Primary Class:
Other Classes:
340/3.7, 340/12.32, 340/310.11, 340/870.02, 340/870.12, 340/870.13, 340/870.24
International Classes:
H02J13/00
View Patent Images:



Description:

My invention relates, generally, to supervisory control and remote metering systems and, more particularly, to systems for performing both supervisory and telemetering functions over a single communication channel.

Heretofore telemetering and supervisory control functions have had to be performed utilizing separate communication channels when the channels were carrier current channels.

An object of my invention is to provide a combined supervisory control and remote metering system which shall function to perform both supervisory control and telemetering operations over a single carrier current communication channel.

Another object of the invention is to provide a combined supervisory control and impulse type remote metering system which shall function to perform impulse selective control and supervisory operations and impulse type telemetering operations employing a single communication channel.

A further object of the invention is to provide an impulse type remote metering system which shall function to so modify and cooperate with previously known selective control systems having a single communication channel as to provide remote selective supervision and control and remote impulse type metering.

These and other objects and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings, the four figures of which, when interconnected as indicated, comprise a diagrammatic view of a combined selective supervisory control and remote metering system embodying the principal features of my invention.

The preferred embodiment of the invention is shown and described herein as it is applied to the supervisory control system of the H. P. Boswau Patent No. 2,208,535, issued July 16, 1940, most of the elements of the system of the Boswau patent being shown in the same cooperative relation herein as in the Boswau patent and the elements bearing the same reference characters as in the Boswau patent drawings.

Certain relays, conductors and other elements of structure have been omitted and others added, and certain relay contact elements have been added to and others omitted from the relays of the Boswau patent. The added elements are designated by reference characters not found in the Boswau patent and the added and altered parts of the system are shown in heavier lines in the drawings so that the invention may be more readily understood.

For convenience of description, to avoid needless repetition, and in order that the invention may be more clearly set forth and understood, reference will be made in this specification to the Boswau Patent No. 2,208,535 for the description of elements and combinations of elements and theff functioning that ard'coffinon ti the two systems and which are fully described in the Boswau patent.

Considering the general aspects of the invention, the system disclosed and described in the Boswau Patent 2,208,535 has been altered by causing it to operate over a carrier current channel in order to show how the invention will function to perform both supervisory control and telemetering operations over a single carrier current signaling channel.

The conductors 219' and 223' are conductors of a power system extending between a control and a remote station. Carrier current impulse sending and receiving devices 502 and 702 at the control and remote stations respectively function to transmit carrier current impulses over the conductors 219' and 223' in response to the actuation of the sending relays 201 and 401 respectively by the supervisory control system, and to respond to carrier current impulses transmitted over the conductors 219' and 223' for supervisory control to actuate the line relays 200 and 400. The sending relays 201 and 401 and the line relays 200 and 400 thus function in a manner similar to the corresponding relays of the system of the Boswau patent referred to hereinbefore.

A telemetering transmitter, which may be similar to that described in the patent to Lenehan No. 2,137,090, issued November 15, 1938, actuates a contact element 104 at the remote station to cause the carrier current device 702 to send.impulses at a frequency proportionate to the quantity measured at the remote station and which is to be indicated at the control station. At the control station an impulse receiver is connected to be actuated by the carrier current responsive device 502 in response to impulses transmitted from the remote station and to actuate an indicator to indicate the quantity measured at the remote station.

Considering the principal aspects of the invention more in detail, the carrier current device 502 at the control station comprises capacitive coupling devices 504 and 506 associated with the power lines 219' and 223' and connected in circult with the high potential winding of a high frequency transformer 503. One low potential winding of the transformer 508 is connected to be energized by an oscillator which functions to generate high frequency currents when its energizing circuit is closed by a contact element 510 of the sending relay 201. Another low potential winding of the carrier current device 502 is connected to energize a relay 512 whose contact element 514 is connected in an energizing circuit for the line relay 200.

At the remote station the carrier current device 702 is similar to the carrier current device 502 and comprises a transformer 708 with its high potential winding connected to capacitive coupling devices 704 and 706, a low potential winding connected to be energized by an oscillator, and another low potential winding connected to energize a relay 712. The oscillator may be controlled to generate impulses by the contact element 703 of the telemetering transmitter or by the contact element 710 of the sending relay 401. The contact element 714 of the relay 712 is connected in the energizing circuit of the line relay 400.

Since the carrier current system is one in which there is no actual connection for current flow between the sending relays 201 and 401 and their associated receiving &ri-hne relays 400 and-240, the system of the Boswau patent has been changed from a closed circuit system, characterized by means for causing the line relays 200 and 400 to be normally energized and operated on each pulse by deenergizing and then reenergizing the relays, to an open circuit system characterized by a normal deenergized condition of the line relays 200 and 400 and operating the line relays by energization and subsequent deenergization on each pulse. Thus when the relays 200 and 400 are connected to negative potential they are pulsed by the relays 512 and 712 whose contact elements 514 and 714 connect their associated relays 200 and 400, respectively, to positive potential. The connections to the contact elements of the line relays 200 and 400 have been reversed so that an impulse comprising energization and deenergization of the line relays 200 and 400 will have the same effect on the supervisory control system as an impulse comprising deenergization and reenergization has on the closed circuit system of the Boswau patent. Thus a control impulse will cause the line relay 200 to break the circuit of the reset relay 202 by energizing the line relay 200 whereas a control impulse will cause the line relay 200 of the Boswau patent to break the circuit of the reset relay 202 by deenergizing the line relay 200.

At the control station the point selecting relay 134 functions by means of its contact element 516 to connect the impulse receiver to be energized by the relay 512. The point selecting relay 310 at the remote station functions through its contact element 716 to connect the contact element 703 of the telemetering transmitter to control the oscillator of the carrier current device 702.

A pendulum relay 518 and an auxiliary relay 520 at the control station function in response to the operation of a telemetering reset key 522 to reset the supervisory control apparatus at the control station by applying an impulse to the system of much longer duration than the supervisory control coding impulses and the telemetering impulses. A pendulum relay 718 and an auxiliary relay 720 at the remote station function in response to the long reset impulse to reset the supervisory control apparatus at the remote station. The pendulum relays 518 and 718 comprise contact making armatures 519 and 719 which, when released by deenergization of the pendulum relays, oscillate to alternately make and break the circuit of their associated time delayed release relays 520 and 720, respectively. The relays 520 and 720 are so timed as to hold in during S0 the interval between break and make of their circuits by the armature 519 and 719 and they drop out a short time after the contact armatures 519 and 719 stop oscillating. The time interval of oscillation of the contact armatures 13 of the pendulum relays 518 and 718 may be several seconds so that they will not cause the release of the relays 520 and 720 when affected by supervisory control or telemetering pulses.

An auxiliary relay 722 at the remote station functions in response to the contact elements 724 and 726 of the relays 403 and 411, respectively, to remove negative potential from the line relay 400. A contact element 728 of the relay 720 also functions to remove negative potential from Sthe line'relay 400.

S In the operation of the system, when it is desired to obtain an indication at the control station of a measured quantity at the remote station, the point operating key-..24 is operated Smomentarily to complete a shunting circuit for the winding of the starting relay 131, and the deenergization of the starting relay 131 will cause the supervisory control apparatus at the control station to energize the pulsing relay 201 with a code which is associated with the control point No. 4 with which point relay 134 is associated, as fully explained in the hereinbefore referred to Boswau patent. The coded pulsing of the sending relay 201 at thecontrol station will cause it to close its contact element 510 to control the oscillator in a circuit which includes the conductors 524 and 526. The oscillator may be any suitable high frequency oscillator which will generate a high frequency potential so long as its 43 circuit is closed. A low potential winding of the transformer 508 is connected to be energized by the oscillator and high potential impulses will be induced in the secondary winding of the transformer 538. The capacitive coupling of the transmission line conductors 219' and 223' with the high potential winding of the transformer 508 through the condensers 504 and 506 will cause the high frequency coded impulses to be transmitted over the transmission line conductors 219' and 223' where they will act upon the high potential winding of a corresponding carrier current transformer through condensers 704 and 706. The receiver relay 712 at the remote station will be affected by the coded impulses, and will actuate its contact armature 714 to energize the line relay 400 in accordance with the coded impulses in a circuit which extends from positive potential through the contact element 714 of the relay 712 in its operated position, a conductor 729, the winding of the line relay 400, conductors 730 and 732, and a contact element 734 of the relay 722 in released position to negative potential.

The coded impulses acting upon the relay 400 will cause the supervisory control apparatus at the remote station to select and operate the point relay 310 which is associated with point No. 4 at the remote station, as fully described in the Boswau patent hereinbefore referred to. The point relay 310 will close its own holding circuit through one of its contact elements and the contact element 437 of the relay 412 as explained in the Boswau patent.

The operation of the point relay 310 at the remote station will cause the supervisory control apparatus at the remote station to intermittently energize the relay 401, whose contact element 110 will intermittently close the oscillator circuit comprising a conductor 736, a conductor 738, contact element 710 and a conductor 740. The oscillator at the remote station will operate through its carrier current transmitting apparatus to transmit to the control station coded impulses associated with the point No. 4 with which the point relay 134 at the control station is associated.

When the coded impulses have been transmitted from the remote station to the control station, the relay 411 at the remote station will be energized, the relay 403 at the remote station will be deenergized, and the contact element 726 and 724 of these relays will complete an energizing circuit for the relay 722 which extends from positive potential through the contact element 726 of the relay 411, a conductor 742, the contact element 724 of the relay 403, a conductor 744, the winding of the relay 722, a conductor 746 and a contact element 748 of the point relay 310 to negative potential. The actuation of-he relay 722 will remove negative return potential from the line relay 400 and prevent it from being operated by impulses received by the receiving relay 712.

The operation of the point relay 310 at the remote station functions to connect the contact element 703 of the telemetering transmitter at the remote station in a control circuit for the oscillator which extends from one terminal of the contact element 703, through a conductor 750, the contact element 716 of the point relay 310, the conductor 736 through the oscillator, the conductors 740 and 752, the contact element 754 of the relay 722 and a conductor 756 to the other terminal of the contact element 703. The contact element 703, which is actuated at a frequency proportional to the quantity measured at the remote station and to be indicated at the control station will thus continuously make and break the control circuit of the oscillator and cause the oscillator to transmit impulses to the control station at a frequency proportional to the metered quantity to be indicated at the control station.

The operation of the point relay 310 also closes an energizing circuit for the pendulum relay 718 at the remote station which extends from positive potential through the contact element 714 of the receiving relay 712 in released position, a conductor 758, the winding of the relay 718, a conductor 760, and a contact element 762 of the point relay 310 to negative potential. The pendulum relay 718 will thus be intermittently energized and deenergized in accordance with the frequency of the telemetering impulses.

When the coded impulses initiated at the remote station by the operation of the point relay 310 and transmitted to the control station over the transmission line are received at the control station, the receiving relay 512 will be actuated in accordance with these coded impulses and will intermittently energize the receiving relay 200 at the control station in a circuit which extends from positive potential through the contact element 514 of the relay 512, a conductor 528, the winding of the relay 200, a conductor 530 and a contact element 532 of the point relay 134 in released position to negative potential. This coded pulsing of the relay 200 will cause the supervisory control apparatus at the control station to select and operate the point relay 134 which will close its own holding circuit comprising its contact element 168 and the contact element 232 of the relay 211 in operating position as explained in the Boswau patent.

The operation of the point relay 134 will connect the impulse receiver at the control station to be energized by the receiving relay 512 in a circuit which extends from positive potential through the contact element 514 of the relay 512, the conductors 528 and 534, the contact element 516 of the point relay 134 and a conductor 536 through the impulse receiver to negative potential. The operation of the point relay 134 will cause its contact element 532 to move to open circuit position to thus remove negative return potential from the relay 200 to prevent it from being pulsed by the telemetering impulses received by the receiving relay 512. The system will thus function to transmit telemetering impulses from the remote station at a frequency proportional to the metered quantity at the station, the impulses will be received at the control station, and the impulse receiver at the control station will be actuated in accUrdance with the o3 frequency of the telemetering impulses. The indicator at the control station which is connected to be actuated by the impulse receiver will indicate at the control station the measured quantity at the remote station.

The pendulum relay 518 at the control station is normally held energized in a circuit which extends from positive potential through a contact element 538 of the relay 520 in released position, a conductor 540 and the winding of the pendulum relay 518 to negative potential.

When it is desired to disconnect the telemetering apparatus associated with point No. 4 at the two stations and restore the supervisory control apparatus to normal, the operator at the control station will operate the telemetering reset key 522 to close an energizing circuit for the relay 520 at the control station extending from positive potential through the reset key 522, a conductor 542, a contact element 544, of the point relay 134, conductors 546 and 548, the contact elements 519 of the pendulum relay 518, a conductor 550 and the winding of the relay 520 to negative potential. This energization of the relay 520 will cause it to move its contact element 538 to actuated position to thus deenergize the pendulum relay 518. The actuation of the relay 520 will cause it to close its own holding circuit which extends from positive potential through the contact element 552 of the relay 520, a conductor 548, cono6 tact elements 519 of the pendulum relay 518, a conductor 550, and the winding of the relay 520 to negative potential. The relay 520 will thus be held actuated for the period required for the oscillating contact elements 519 of the pendulum relay 518 to cease oscillating and to thereby break the holding circuit of the relay 520. The actuation of the relay 520 will complete an energizing circuit for the pulsing relay 201 which extends from positive potential through the contact element 538 in operated position, a conductor 554 and the winding of the relay 201 to negative potential. The relay 201 will thus close its contact element 510 to cause a long impulse to be transmitted to the remote station. The actuation of the relay 520 will also close a connection to negative potential for the line relay 200 which extends from positive potential through the contact element 514 of the relay 512 which will be energized by the long pulse caused by the energization of the relay 201, the conductor 528, the winding of the relay 200, the conductor 530, a conductor 555 and a contact element 558 of the relay 520 to negative potential.

The long impulse applied to the line relay 200 will cause it to actuate its contact element 227 to break the circuit of the reset relay 202 which will permit its armature 228 to be released to break the indirect positive connection of the supervisory control system at the control station to thus reset the supervisory control apparatus and return the control apparatus to normal. The breaking of the connection to indirect positive will interrupt the holding circuit of the point relay 134 which, as described hereinbefore, includes the contact element 232 of the relay 211.

At the end of the interval of oscillation of the contact element 519 of the relay pendulum 518, the contact elements of the relay 520 will be released and an energizing circuit will again be established for the pendulum relay 518 by the contact element 538 of the relay 520 in released position.

When the long release impulse is received at the remote station, receiving relay 712 will be energized for the interval of this release impulse, thus breaking the circuit of the pendulum relay 718 by the movement of the contact element 714 of the relay 712 to operated position. After an interval determined by the period of oscillation of the contact elements 719 of the pendulum relay 718, the relay 720 will release to close an energizing circuit for the line relay 400 which extends from positive potential through the contact element 714 of the relay 712, the conductor 729, the winding of the relay 400, the conductors 730 and 732, the contact element 728 of the relay 720, a conductor 764 and the contact element 734 of the relay 722 in actuated position, to negative potential. The release impulse will be so timed as to be sufficiently long as to cause the receiving relay 712 to maintain the relay 400 energized until the reset relay 402 whose circuit is broken by the actuation of the contact element 420 of the relay 400 to release its contact element 421 to thus reset the supervisory control apparatus at the remote station by removing the indirect positive connection as fully described in the hereinbefore referred to Boswau patent.

The point relay 310 at the remote station will be released by the disconnection of the indirect positive connection which formed a part of its holding circuit through the contact element 437 of the relay 412. The deenergization of the point relay 310 will permit its contact element 716 to break the energizing circuit for the oscillator which was controlled by the contact element 703 sf the telemetering transmitter. The contact element 762 of the point relay 310 will interrupt the energizing circuit for the pendulum relay 718 so that it will not be again energized when the contact element 7i 4 of the relay 712 is released at the end of the release impulse. The release of the contact element 748 of the point relay 3!0 will interrupt the energizing circuit of the relay 722 and permit its contact element 734 to again restore negative return potential to the line relay 400.

After these operations, the supervisory control apparatus at both stations will be in normal position ready to be utilized for point selection and operation over other supervisory control points or telemetering over any other control point with which similar telemetering apparatus may be associated.

It is to be understood that the pendulum relays 518 and 718 are merely illustrative of one type of relay by which a considerable time delay release may be provided and that any equivalent time delay relay may be used to perform the function of these pendulum relays. It is also to be understood that the telemetering transmitter at the remote station may be any suitable means for operating the contact element 703 at a frequency proportional to the quantity at the remote station which is to be indicated at the control station, and that the impulse receiver at the control station may be any suitable device which will respond to and be actuated in accordance with the frequency of impulses applied thereto. It is to be further understood that the carrier current apparatus illustrated and described herein is merely illustrative of the form which this apparatus may take, and that this apparatus may be any apparatus which will transmit impulses Sbetween two stations whether or not there be a direct conductor connection between the stations.

Thus it will be seen that I have provided a combined supervisory control and impulse type -remote metering system which -haRlfunction to perform impulse selection control and supervisiory operations and impulse type telemetering operations between two stations employing but a single communication channel.

In compliance with the requirements of the patent statutes, I have shown and described herein the preferred embodiments of my invention. It is to be understood, however, that the invention is not limited to the precise construction herein disclosed, but is capable of modification by one skilled in the art, the embodiments herein disclosed being merely illustrative of the principles of my invention.

I claim as my invention: 1. In a combined supervisory control and remote metering system, a carrier current channel extending between a control station and a remote station, supervisory control means at the stations, means including said superviosry control means for selectively operating from the control station over the carrier current channel a plurality of point relays at the remote station, means including said supervisory control means responsive to the operation of a selected point relay at the remote station for operating a corre.5 sponding point relay at the control station, an impulse device at the remote station operable at a frequency proportional to a quantity to be indicated at the control station for transmitting telemetering impulses from the remote to the Co control station over said carrier current channel at frequencies proportional to the said quantity, means responsive to the operation of said selected point relay at the remote station for connecting said impulse-device at the remote station in transmitting relation, frequency responsive means at the control station responsive to the frequency of the impulses transmitted from the remote station, means responsive to the operation of the said corresponding point relay at the control station for connecting said frequency responsive means to be actuated by the impulses transmitted from the remote station, means at the control station for applying a release impulse to the supervisory control means of longer duration than any of the quantity indicating impulses, and means responsive to the application of such a release impulse only to the supervisory control means for deenergizing said operated point relays at the control and remote stations.

2. In a combined supervisory control and remote metering system, a carrier current channel extending between a control station and a remote station, supervisory control means at the stations operable in response to selective coded impulses, means including said supervisory control means for selectively operating by coded impulses sent from the control station over the carrier current channel a plurality of point relays at the remote station, means including said supervisory control means responsive to the operation of one of said point relays at the remote station for operating a corresponding point relay at the control station, an impulse device at the remote station operable in accordance with a quantity to be indicated at the control station for transmitting telemetering impulses from the remote to the control station over said carrier current channel at frequencies proportional to the said quantity, means responsive to the operation of said one selected point relay at the remote station for connecting said impulse device at the remote station in impulse transmitting relation, frequency responsive means at the control station responsive to the l'relquency of the impLDies transmitted from the remote station, means responsive to the operation of the said corresponding point relay at the control station for connecting said frequency responsive means to be actuated by the impulses transmitted from the remote station, means at the control station for applying a release impulse to the supervisory control means of longer duration than any of the quantity indicating impulses, and means responsive to the application of such a release impulse only to the supervisory control means for deenergizing said operated point relays at the ccntrol and remote stations.

3. In a combined control and remote metering system, a communication system connecting a control and a remote station, control means at the stations operable in response to selective coded impulses, means including said control means for selectively operating by coded impulses sent from the control station over said communication system a plurality of point relays at the remote station, means including said control means responsive to the operation of one of said point relays at the remote station for operating a corresponding point relay at the control station, an impulse device at the remote station operable in accordance with a quantity to be indicated at the control station for transmitting telemetering impulses from the remote to the control station over said communication system at frequencies proportional to the said quantity, means responsive to the operation of said one selected point relay at the remote station for connecting said impulse device at the remote station in impulse transmitting relation with said communication system, frequency responsive means at the control station responsive to the frequency of the impulses transmitted from the remote station, means responsive to the operation of the said corresponding point relay at the control station for connecting said frequency responsive means to be actuated by the impulses transmitted from the remote station, means at the control station for applying a release impulse to the said control means of longer duration than any of the quantity indicating impulses, and means responsive to the application of such a release impulse only to the said control means for deenergizing said operated point relays at the control and remote stations.

4. In a combined control and remote metering system, a communication system connecting a control and a remote station, control means at the stations operable in response to selective coded impulses, means including said control means for selectively operating by coded impulses sent from the control station over said communication system a plurality of point relays at the remote station, means including said control means responsive to the operation of one of said point relays at the remote station for operating a corresponding point relay at the control station, means responsive to the operation of the means for operating said corresponding point relay at the control station for rendering said control means at the remote station unresponsive to impulses on the communication system, means responsive to the operation of the said corresponding point relay at the control station for rendering the said control means at the control station unresponsive to impulses on the communication system, an impulse device at the remote station operable in accordance with a quantity to be indicated at the control station for transmitting telemetering impulses T-om the remote to the control station over said communication system at frequencies proportional to the said quantity, means responsive to the operation of said one selected point relay at the remote station for connecting said impulse device in impulse transmitting relation with the communication system, frequency responsive means at the control station responsive to the frequency of the impulses transmitted from the remote station, and means responsive to the operation of the said corresponding point relay at the control station for connecting said frequency responsive means to be actuated by the impulses transmitted from the remote station.

5. In a combined control and remote metering system, a communication system connecting a control and a remote station, control means at the stations operable in response to selective coded impulses, means including said control means for selectively operating by coded impulses sent from the control station over said communication system a plurality of point relays at the remote station, means including said control means responsive to the operation of one of said point relays at the remote station for operating a corresponding point relay at the control station, means responsive to. the operation of the means for operating said corresponding point relay at the control station for rendering said control means at the remote station unresponsive cG to impulses on the communication system, means responsive to the operation of the said corresponding point relay at the control station for rendering the said control means at the control station unresponsive to impulses on the commuU5 nication system, an impulse device at the remote station operable in accordance with a quantity to be indicated at the control station for transmitting telemetering impulses from the remote to the control station over said communication system at frequencies proportional to the said quantity, means responsive to the operation of said one selected point relay at the remote station for connecting said impulse device in impulse transmitting relation with the communication system, frequency responsive means at the 9 I , , control station responsive to the frequency of the impulses transmitted from the remote station, means responsive to the operation of the said corresponding point relay at the control station for connecting said frequency responsive means to be actuated by the impulses transmitted from the remote station, means at the control station for applying a release impulse to the communication system of longer duration than any of the quantity indicating impulses, and means responsive to the application of such a release impulse only to the communication system for deenergizing said point relays and restoring said control means to impulse responsive condition.

6. In a combined remote control and remote metering system, a communication system connecting a control and a remote station, an impulse means at the remote station for transmitting impulses over the communication system at frequencies proportional to a quantity to be indicated at the control station, means operable over said communication system from the control station for connecting said impulse means in impulse transmitting relation with said communication system, an impulse responsive means at the control station, means for connecting said impulse responsive means in impulse receiving relation with said communication system, means for applying a release impulse to the communication system of longer duration than any of the quantity indicating impulses, and means responsive only to such a release impulse on said communication system for disconnecting said impulse transmitting and receiving means from transmitting and receiving relation with the communication system.

7. In a combined control and remote metering system, a communication system connecting a control and a remote station, control means at the stations operable in response to selective coded impulses, means including said control means for selectively operating by coded impulses sent from the control station over said communication system a plurality of point relays at the remote station, means including said control means responsive to the operation of one of said point relays at the remote station for operating a corresponding point relay at the control station, an impulse device at the remote station operable in accordance with a quantity to be indicated at the control station for transmitting telemetering impulses from the remote to the control station over said communication system at frequencies proportional to the said quantity, means responsive to the operation of said one selected point relay at the remote station for connecting said impulse device at the remote station in impulse transmitting relation with said communication system, frequency responsive means at the control station responsive to the frequency of the impulses transmitted from the remote station, means responsive to the operation of the said corresponding point relay at the control station for connecting said frequency responsive means to be actuated by the impulses transmitted from the remote station, means at the control station for applying a release impulse to the control means of longer duration than any of the quantity indicating impulses, and means responsive to the application of such a release impulse only to the said control means for deenergizing said operated point relays af the iu control and remote stations, said means responsive to a release impulse comprising reset means at the control and remote stations for deenergizing said operated point relays at the control and remote stations.

8. In a combined control and remote metering system, a communication system connecting a control and a remote station, control means at the stations operable in response to selective coded.impulses, means including_ said control means for selectively operating by coded impulses sent from the control station over said communication system a plurality of point relays at the remote station, means including said control means responsive to the operation of one of said point relays at the remote station for operating a corresponding point relay at the control station, an impulse device at the remote station operable in accordance with a quantity to be indicated dt the control station-'for  ransmitting telemetering impulses from the remote to the control station over said communication system at frequencies proportional to the said quantity, means responsive to the operation of said one selected point relay at the remote station for connecting said impulse device at the remote station in impulse transmitting relation with said communication system, frequency responsive means at the control station responsive to the frequency of the impulses transmitted from the remote station, means responsive to the operation of the said corresponding point relay at the control station for connecting said frequency responsive means to be actuated by the impulses transmitted from the remote station, means at the control station for applying a release impulse to the control means of longer duration than any of the quantity indicating impulses, and means responsive to the application of such a release impulse only to the said control means for deenergizing said operated point relays at the control and remote stations, said release impulse applying means comprising a first relay and a second relay, said first relay being normally energized, means for momentarily energizing said second relay, means whereby energization of said second relay deenergizes said first relay, means whereby the deenergization of said first relay causes said second relay to be energized for a predetermined length of time, and means whereby said second relay causes an impulse to be applied to the control means for the duration of the energization of the second relay.

WILLARD A. DERR.

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