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US3258653A - Device for controlling a monitoring relay - Google Patents

Device for controlling a monitoring relay Download PDF

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US3258653A
US3258653A US3258653DA US3258653A US 3258653 A US3258653 A US 3258653A US 3258653D A US3258653D A US 3258653DA US 3258653 A US3258653 A US 3258653A
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load device
state
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gate circuit
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B61—RAILWAYS
    • B61L—GUIDING RAILWAY TRAFFIC; ENSURING THE SAFETY OF RAILWAY TRAFFIC
    • B61L29/00—Safety means for rail/road crossing traffic
    • B61L29/24—Means for warning road traffic that a gate is closed or closing, or that rail traffic is approaching, e.g. for visible or audible warning
    • B61L29/28—Means for warning road traffic that a gate is closed or closing, or that rail traffic is approaching, e.g. for visible or audible warning electrically operated
    • B61L29/288—Wiring diagram of the signal control circuits

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  • the invention relates to a device for controlling a monitoring relay by means of a monitoring signal.
  • Such a monitoring relay is employed inter alia in a safety system for railways, for example, for the electronic indication of the passage of a train at a given point, for controlling level-crossing signals, barriers and the like.
  • a safety system for railways for example, for the electronic indication of the passage of a train at a given point, for controlling level-crossing signals, barriers and the like.
  • high requirements are made on reliability and safety so that, if a disturbance occurs somewhere in the system, for example, a failure in the energizing circuit of a relay or if the supply voltage drops out, accidents will not occur.
  • use is commonly made of a rest current. This means that the monitoring relay is normally energized under the control of a monitoring signal and is temporarily deenergized at the passage of a train which temporarily interrupts the monitoring signal.
  • the monitoring signal is supplied to the relay via a gate circuit which is normally conducting under the control of a voltage picked up between the gate and the relay.
  • a gate circuit which is normally conducting under the control of a voltage picked up between the gate and the relay.
  • an energizinlg circuit is closed via a delay circuit independently of the condition of said gate circuit.
  • the drawing shows diagrammatically part of a mainly electronic monitoring circuit for the indication of the passage of a train.
  • a continuously running oscillator B which supplies normally a monitoring signal to an input terminal 1 of the And-gate P
  • the monitor signal appears at the output terminal 2 of And-gate P and is coupled to one input terminal 3 of the Or-gate P
  • Output terminal 4 of Or-gate P supplies the monitor signal to the input of the amplifier C, which amplifies and rectifies the signal.
  • the output of amplifier C is connected to the input terminal 8 of a relay R.
  • the monitoring relay R is therefore normally energized under the action of the direct output voltage of the amplifier device C.
  • This direct voltage may be supplied via a feedback path T to a second input terminal of And-gate P to control the condition thereof.
  • the direct voltage controls the gate P so that this gate is normally conducting or open when the direct voltage is present at terminal 5 and thereby passes the monitoring signal of the oscillator B.
  • Oscillator B may be of the general type disclosed in US. Patent 2,105,930, which issued January 18, 1938.
  • the And-gate P may be chosen from among the circuits disclosed at pages 400, 436 and 437 of the text book Pulse and Digital Circuits by Millman and T aub (McGraw- Hill Book Co., 1956). Suitable circuits for Or-gate P are shown at page 396 of the Millman and T-aub book or at pages 642 and 643 of Waveforms, vol.
  • Amplifier C may Patented June 28, 1966 be chosen from among the amplifier circuits described in chapters 6 and 7 of the text book Radio Engineering by F. E. Terrnan, third edition (McGraw-Hill Book Co., 1947).
  • the oscillator B is arranged so that at the passage of a train, given parts thereof, for example, the flanges of the wheels, pass closely by the tuned circuit of the oscillator, which is thus damped or detuned, or at any rate is acted upon so that the signal is not passed by the device C and the direct output voltage at the point 6 disappears. Consequently, the gate P is closed so that, if the monitoring signal of the oscillator should immediately thereafter reappear, the gate P can no longer pass this signal and the relay R must remain de-energized.
  • a warning signal is supplied to a further safety arrangement (not shown), which subsequently carries out given controloperations, for example, the closure of barriers, the transition of semaphores to danger and the like.
  • auxiliary energizing circuit for the relay R from the supply source V.
  • the auxiliary voltage is suppliedifrom the source V to the relay R via contact r2, the delay device D, the gate P and the amplifier C.
  • the supply source V may be an alternating current source, in which case the delay device D may be an artificial line of the type shown at page 291 of the aforementioned Pulse and Digital Circuits or a direct voltage source, the delay device comprising for example an oscillator which is made operative with a given delay.
  • the delayed auxiliary signal is coupled from the output of delay element D to a second input terminal 7 of Or-gate P through the gate to output terminal 4 and then to the input of amplifier C.
  • a direct voltage is produced at the output of said amplifier so that the relay R is reenergized and the gate P is again rendered conducting.
  • the relay R remains energized under the control of the monitoring signal supplied by the oscillator B, and the initial state is restored.
  • the relay R after its de-energization, cannot be immediately re'energized owing to the presence of the delay circuit D.
  • the delay time thereof is such that the relay must always remain de-energized for a given time which is sufficient to insure that the circuits which must respond to the de-energization of the relay R have a sufficient time to respond.
  • alternating current signals for controlling the relay R. It is also within the scope of the invention to employ direct current signals instead of AC. signals to control the relay.
  • direct current signals instead of AC. signals to control the relay.
  • the use of alternating current has various advantages.
  • an electronic train detector in the form of the oscillator B may be employed to which no moving parts are connected.
  • train detectors operating with switches controlled mechanically by the train have the disadvantage that in spite of a careful construction damage thereto frequently occurs in practice.
  • Signal control apparatus comprising means for generating a monitor signal in response to an external condition, a load device having an input terminal for a control signal, said load device having first and second 0perative states determined by the condition of said control signal at its input terminal, gate circuit means having input means and output means and connected between said signal generating means and said load device input terminal for controlling the passage of said monitor signal from said signal generating means to said load device, circuit means responsive to the presence of said monitor signal at said output means for supplying a control signal to said gate circuit input means thereby to maintain said gate circuit in its open condition, said monitor signal further controlling said load device into said first state, and means responsive to the state of said load device for supplying a delayed control signal to said gate circuit input means when said load device is in said second state.
  • Apparatus as described in claim 1 further comprising means for coupling said delayed control signal to said load device input terminal thereby to return said load device to said first state.
  • Signal control apparatus comprising means responsive to an external condition for generating a monitor signal, a load device having a first normally energized state and a second state and including an input terminal for a control signal which controls the state thereof, gate circuit means having input means and output means, means for coupling said monitor signal from said signal generating means to said gate circuit input means, circuit means for coupling said gate circuit output means to said load device input terminal, said circuit means further comprising means for supplying a control signal to said gate circuit input means for controlling the condition of said gate circuit as a function of said monitor signal, delay means having an input and an output, means responsive to the state of said load device for supplying a signal to the input of said delay means when said load device is in said second state, and means coupling a delayed signal from the output of said delay means to said gate circuit input means thereby to open said gate circuit.
  • Signal control apparatus comprising means for selectively generating a monitor signal in response to an external manifestation, a load device having an input terminal for a control signal, said load device being responsive to a control signal applied thereto for selectively controlling said load device into a first and second state, gate circuit means having first and second input terminals and an output terminal, means for coupling said monitor signal from said signal generating means to said gate circuit first input terminal, circuit means for coupling said gate circuit output terminal to said load device input terminal, said circuit means further comprising means for supplying a control signal to said gate circuit second input terminal for controlling the passage of said monitor signal through said gate circuit means, delay means having an input and an output, means responsive to the state of said load device for supplying a signal to the input of said delay means when said load device is in said second state, said circuit means further comprising means coupling the output of said delay means to said load device input and to said gate circuit second input terminal to supply thereto a delayed control signal, said delayed control signal being operative to open said gate circuit and also to return said load device to said first state
  • Signal control apparatus comprising means for selectively generating a monitor signal determined by an external condition, a load device having an input terminal for a control signal, said load device having a first normally energized state and a second state corresponding to the presence and absence of a control signal at said input terminal, respectively, gate circuit means having first and second' input terminals and an output terminal, means for coupling said monitor signal from said signal generating means to said gate circuit firs-t input terminal, circuit means for coupling said gate circuit output terminal to said load device input terminal and to said gate circuit second input terminal whereby the presence of said monitor signal at said output terminal maintain-s said gate circuit open and said load device in said first normally energized state, and means responsive to the state of said load device for supplying a delayed control signal to said gate circuit second input terminal and to said load device input terminal when said load device is in said second state, said delayed control signal being operative to open said gate circuit and also to return said load device to said first state.
  • circuit means further comprises an OR gate having first and second input terminals and an output terminal, means connecting said OR gate first input terminal to said gate circuit output terminal, means coupling said delayed control signal to said OR gate second input terminal, and means coupling said OR gate output terminal to said load device input terminal and to said gate circuit second input terminal.
  • a train control system for a section of railway track comprising means positioned along said track in electroresponsive coupling relationship with a passing train for producing a monitor signal, a load device which is selectively operable between first and second states in response to a control signal applied thereto, a gating device having input means and output means, means connecting said gating device between said signal producing means and said load device so as to effectively control the passage of said monitor signal to said load device, means coupled to said gating device output means for supplying a control signal to said gating device input means to control the condition of said gating device as a function Otf said monitor signal, said signal producing means being responsive to a passing train to cause a change in the monitor signal produced thereby to actuate said control signal supplying means to close said gating device and change said load device from said first to said second state, and means responsive to the state of said load device for supplying a delayed control signal to said gating device input means in the second state of said load device thereby to open said gating device to said monitor
  • Apparatus for detecting the presence of a train in a given section of railway track comprising, means located near said track and responsive to a passing train for producing a monitor signal having first and second electrical characteristics determined by the absence and presence, respectively, of a train in said given track section, output means responsive to said monitor signal and having first and second operative states corresponding to said first and second characteristics of said monitor signal, respectively, gating means connected between said signal producing means and said output means for effectively controlling the passage of said monitor signal from said signal producing means to said out-put means, means connected to the output of said gating means for supplying a control signal to said gating means for controlling the condition of said gating means as a function of the monitor signal thereat, said output means and said control signal supplying means being responsive to said monitor signal second characteristic to change over said output means from said first state to said second state and to close said gating means, respectively, means responsive to the state of said output means for applying a delayed control signal to said gating means in the second state of said output means and independently of said
  • Apparatus as described in claim 8 further comprising means for coupling said delayed control signal to said output means thereby to cause said output means to change over from said second state to said first state.
  • Apparatus for detecting the presence of a train in a given section of railway track comprising, oscillation means located near said track and responsive to a passing train for producing an oscillation signal having first and second oscillation conditions determined by the absence and presence, respectively, of a train in said given track section, a load device responsive to a control signal and having a first normally energized state corre sponding to said first oscillation condition and a second state corresponding to said second oscillation condition, a switching device having input means connected to the output of said oscillation means and including output means for said oscillation signal, circuit means interconnecting said switching device output means and input means, said circuit means including means responsive to said oscillation signal at said output means for supplying a control signal to said load device and to said switching device to control the condition thereof, said circuit means being responsive to said first oscillation condition at said switching device output means to control said switching device into a closed condition and said load device into said first state and being responsive to said second oscillation condition at said output means to control said load device into said second state and said switching device

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Train Traffic Observation, Control, And Security (AREA)

Description

June 28, 1966 J. FOSSE ETAL 3,258,653
DEVICE FOR CONTROLLING A MONITORING RELAY Filed Aug. 15. 1962 INVENTORQ .mcouss' FOSSE LOUIS DEsPRE;
BY 3 AGE United States Patent "ice 3,258,653 DEVICE FOR CONTROLLING A MONITORING RELAY Jacques Foss, Argenteuil, and Louis Deprez, Paris, France, assiguors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Aug. 13, 1962, Ser. No. 216,427 10 Claims. (Cl. 317146) The invention relates to a device for controlling a monitoring relay by means of a monitoring signal.
Such a monitoring relay is employed inter alia in a safety system for railways, for example, for the electronic indication of the passage of a train at a given point, for controlling level-crossing signals, barriers and the like. In such systems high requirements are made on reliability and safety so that, if a disturbance occurs somewhere in the system, for example, a failure in the energizing circuit of a relay or if the supply voltage drops out, accidents will not occur. In order to provide fail-safe operation, use is commonly made of a rest current. This means that the monitoring relay is normally energized under the control of a monitoring signal and is temporarily deenergized at the passage of a train which temporarily interrupts the monitoring signal. If the train has a high speed, this interruption will take only a very short time, so that the relay remains de-energized only for a short time. It is, however, very important that both the relay and the relay-controlled further safety arrangement should respond with certainty to the interruption of the monitoring signal of the relay, even if this interruption takes only a very short time.
The invention provides a reliable solution to this problem. In accordance with the invention, the monitoring signal is supplied to the relay via a gate circuit which is normally conducting under the control of a voltage picked up between the gate and the relay. In the deenergized or rest position of the relay, an energizinlg circuit is closed via a delay circuit independently of the condition of said gate circuit.
The invention will be described more fully with reference to the embodiment shown in the figure.
The drawing shows diagrammatically part of a mainly electronic monitoring circuit for the indication of the passage of a train. In the proximity of the rails A1, A2 there is arranged a continuously running oscillator B, which supplies normally a monitoring signal to an input terminal 1 of the And-gate P The monitor signal appears at the output terminal 2 of And-gate P and is coupled to one input terminal 3 of the Or-gate P Output terminal 4 of Or-gate P supplies the monitor signal to the input of the amplifier C, which amplifies and rectifies the signal. The output of amplifier C is connected to the input terminal 8 of a relay R. The monitoring relay R is therefore normally energized under the action of the direct output voltage of the amplifier device C. This direct voltage may be supplied via a feedback path T to a second input terminal of And-gate P to control the condition thereof. The direct voltage controls the gate P so that this gate is normally conducting or open when the direct voltage is present at terminal 5 and thereby passes the monitoring signal of the oscillator B. Oscillator B may be of the general type disclosed in US. Patent 2,105,930, which issued January 18, 1938. The And-gate P may be chosen from among the circuits disclosed at pages 400, 436 and 437 of the text book Pulse and Digital Circuits by Millman and T aub (McGraw- Hill Book Co., 1956). Suitable circuits for Or-gate P are shown at page 396 of the Millman and T-aub book or at pages 642 and 643 of Waveforms, vol. 19 of the Radiation Laboratory series edited by Britton Chance et al. (McGraw-Hill Book Co., 1949). Amplifier C may Patented June 28, 1966 be chosen from among the amplifier circuits described in chapters 6 and 7 of the text book Radio Engineering by F. E. Terrnan, third edition (McGraw-Hill Book Co., 1947).
The oscillator B is arranged so that at the passage of a train, given parts thereof, for example, the flanges of the wheels, pass closely by the tuned circuit of the oscillator, which is thus damped or detuned, or at any rate is acted upon so that the signal is not passed by the device C and the direct output voltage at the point 6 disappears. Consequently, the gate P is closed so that, if the monitoring signal of the oscillator should immediately thereafter reappear, the gate P can no longer pass this signal and the relay R must remain de-energized.
Via contacts r1 of the relay R, a warning signal is supplied to a further safety arrangement (not shown), which subsequently carries out given controloperations, for example, the closure of barriers, the transition of semaphores to danger and the like.
Moreover, in the de-energized state of the relay R, there is closed, via the break contact r2 thereof, or of a further relay, an auxiliary energizing circuit for the relay R from the supply source V. The auxiliary voltage is suppliedifrom the source V to the relay R via contact r2, the delay device D, the gate P and the amplifier C. The supply source V may be an alternating current source, in which case the delay device D may be an artificial line of the type shown at page 291 of the aforementioned Pulse and Digital Circuits or a direct voltage source, the delay device comprising for example an oscillator which is made operative with a given delay. The delayed auxiliary signal is coupled from the output of delay element D to a second input terminal 7 of Or-gate P through the gate to output terminal 4 and then to the input of amplifier C. Under the action of the. signal supplied to the amplifier C, a direct voltage is produced at the output of said amplifier so that the relay R is reenergized and the gate P is again rendered conducting. After the contact r2 is re-opened, the relay R remains energized under the control of the monitoring signal supplied by the oscillator B, and the initial state is restored. However, if the oscillator monitoring signal had not yet returned in the meantime, the opening of the auxiliary energizing circuit by means of the contact r2 would cause a de-energization of the relay R, after which the process is repeated until the oscillator monitoring signal reappears.
As stated above, the relay R, after its de-energization, cannot be immediately re'energized owing to the presence of the delay circuit D. The delay time thereof is such that the relay must always remain de-energized for a given time which is sufficient to insure that the circuits which must respond to the de-energization of the relay R have a sufficient time to respond.
In the embodiment described above use is made of. alternating current signals for controlling the relay R. It is also within the scope of the invention to employ direct current signals instead of AC. signals to control the relay. The use of alternating current, however, has various advantages. For example, an electronic train detector in the form of the oscillator B may be employed to which no moving parts are connected. Known train detectors operating with switches controlled mechanically by the train have the disadvantage that in spite of a careful construction damage thereto frequently occurs in practice.
What is claimed is:
1. Signal control apparatus comprising means for generating a monitor signal in response to an external condition, a load device having an input terminal for a control signal, said load device having first and second 0perative states determined by the condition of said control signal at its input terminal, gate circuit means having input means and output means and connected between said signal generating means and said load device input terminal for controlling the passage of said monitor signal from said signal generating means to said load device, circuit means responsive to the presence of said monitor signal at said output means for supplying a control signal to said gate circuit input means thereby to maintain said gate circuit in its open condition, said monitor signal further controlling said load device into said first state, and means responsive to the state of said load device for supplying a delayed control signal to said gate circuit input means when said load device is in said second state.
2. Apparatus as described in claim 1 further comprising means for coupling said delayed control signal to said load device input terminal thereby to return said load device to said first state.
3. Signal control apparatus comprising means responsive to an external condition for generating a monitor signal, a load device having a first normally energized state and a second state and including an input terminal for a control signal which controls the state thereof, gate circuit means having input means and output means, means for coupling said monitor signal from said signal generating means to said gate circuit input means, circuit means for coupling said gate circuit output means to said load device input terminal, said circuit means further comprising means for supplying a control signal to said gate circuit input means for controlling the condition of said gate circuit as a function of said monitor signal, delay means having an input and an output, means responsive to the state of said load device for supplying a signal to the input of said delay means when said load device is in said second state, and means coupling a delayed signal from the output of said delay means to said gate circuit input means thereby to open said gate circuit.
4. Signal control apparatus comprising means for selectively generating a monitor signal in response to an external manifestation, a load device having an input terminal for a control signal, said load device being responsive to a control signal applied thereto for selectively controlling said load device into a first and second state, gate circuit means having first and second input terminals and an output terminal, means for coupling said monitor signal from said signal generating means to said gate circuit first input terminal, circuit means for coupling said gate circuit output terminal to said load device input terminal, said circuit means further comprising means for supplying a control signal to said gate circuit second input terminal for controlling the passage of said monitor signal through said gate circuit means, delay means having an input and an output, means responsive to the state of said load device for supplying a signal to the input of said delay means when said load device is in said second state, said circuit means further comprising means coupling the output of said delay means to said load device input and to said gate circuit second input terminal to supply thereto a delayed control signal, said delayed control signal being operative to open said gate circuit and also to return said load device to said first state.
5. Signal control apparatus comprising means for selectively generating a monitor signal determined by an external condition, a load device having an input terminal for a control signal, said load device having a first normally energized state and a second state corresponding to the presence and absence of a control signal at said input terminal, respectively, gate circuit means having first and second' input terminals and an output terminal, means for coupling said monitor signal from said signal generating means to said gate circuit firs-t input terminal, circuit means for coupling said gate circuit output terminal to said load device input terminal and to said gate circuit second input terminal whereby the presence of said monitor signal at said output terminal maintain-s said gate circuit open and said load device in said first normally energized state, and means responsive to the state of said load device for supplying a delayed control signal to said gate circuit second input terminal and to said load device input terminal when said load device is in said second state, said delayed control signal being operative to open said gate circuit and also to return said load device to said first state.
6. Apparatus as described in claim 5 wherein said circuit means further comprises an OR gate having first and second input terminals and an output terminal, means connecting said OR gate first input terminal to said gate circuit output terminal, means coupling said delayed control signal to said OR gate second input terminal, and means coupling said OR gate output terminal to said load device input terminal and to said gate circuit second input terminal.
7. A train control system for a section of railway track, comprising means positioned along said track in electroresponsive coupling relationship with a passing train for producing a monitor signal, a load device which is selectively operable between first and second states in response to a control signal applied thereto, a gating device having input means and output means, means connecting said gating device between said signal producing means and said load device so as to effectively control the passage of said monitor signal to said load device, means coupled to said gating device output means for supplying a control signal to said gating device input means to control the condition of said gating device as a function Otf said monitor signal, said signal producing means being responsive to a passing train to cause a change in the monitor signal produced thereby to actuate said control signal supplying means to close said gating device and change said load device from said first to said second state, and means responsive to the state of said load device for supplying a delayed control signal to said gating device input means in the second state of said load device thereby to open said gating device to said monitor signal.
8. Apparatus for detecting the presence of a train in a given section of railway track comprising, means located near said track and responsive to a passing train for producing a monitor signal having first and second electrical characteristics determined by the absence and presence, respectively, of a train in said given track section, output means responsive to said monitor signal and having first and second operative states corresponding to said first and second characteristics of said monitor signal, respectively, gating means connected between said signal producing means and said output means for effectively controlling the passage of said monitor signal from said signal producing means to said out-put means, means connected to the output of said gating means for supplying a control signal to said gating means for controlling the condition of said gating means as a function of the monitor signal thereat, said output means and said control signal supplying means being responsive to said monitor signal second characteristic to change over said output means from said first state to said second state and to close said gating means, respectively, means responsive to the state of said output means for applying a delayed control signal to said gating means in the second state of said output means and independently of said gating means thereby to open said gating means.
9. Apparatus as described in claim 8 further comprising means for coupling said delayed control signal to said output means thereby to cause said output means to change over from said second state to said first state.
10. Apparatus for detecting the presence of a train in a given section of railway track comprising, oscillation means located near said track and responsive to a passing train for producing an oscillation signal having first and second oscillation conditions determined by the absence and presence, respectively, of a train in said given track section, a load device responsive to a control signal and having a first normally energized state corre sponding to said first oscillation condition and a second state corresponding to said second oscillation condition, a switching device having input means connected to the output of said oscillation means and including output means for said oscillation signal, circuit means interconnecting said switching device output means and input means, said circuit means including means responsive to said oscillation signal at said output means for supplying a control signal to said load device and to said switching device to control the condition thereof, said circuit means being responsive to said first oscillation condition at said switching device output means to control said switching device into a closed condition and said load device into said first state and being responsive to said second oscillation condition at said output means to control said load device into said second state and said switching device References Cited by the Examiner UNITED STATES PATENTS STEPHEN W. CAPELLI, Primary Examiner.
SAMUEL BERNSTEIN, Examiner.
L. T. HIX, Assistant Examiner.
4/1963 Kaehms 317-146 XRV

Claims (1)

1. SIGNAL CONTROL APPARATUS COMPRISING MEANS FOR GENERETING A MONITOR SIGNAL IN RESPONSE TO AN EXTERNAL CONDITION, A LOAD DEVICE HAVING AN INPUT TERMINAL FOR A CONTROL SIGNAL, SAID LOAD DEVICE HAVING FIRST AND SECOND OPERATIVE STATES DETERMINED BY THE CONDITION OF SAID CONTROL SIGNAL AT ITS INPUT TERMINAL, GATE CIRCUIT MEANS HAVING INPUT MEANS AND OUTPUT MEANS AND CONNECTED BETWEEN SAID SIGNAL GENERATING MEANS AND SAID LOAD DEVICE INPUT TERMINAL FOR CONTROLLING THE PASSAGE OF SAID MONITOR SIGNAL FROM SAID SIGNAL GENERATING MEANS TO SAID LOAD DEVICE, CIRCIUT MEANS RESPONSIVE TO THE PRESENCE OF SAID MONITOR SIGNAL AT SAID OUTPUT MEAND FOR SUPPLYING A CONTROL SIGNAL TO SAID GATE CIRCUIT INPUT MEANS THEREBY TO MAINTAING SAID GATE CIRCUIT IN ITS OPEN CONDITION, SAID MONITOR SIGNAL FURTHER CONTROLLING SAID LOAD DEVICE INTO SAID FIRST STATE, AND MEANS RESPONSIVE TO THE STATE OF SAID LOAD DEVICE FOR SUPPLYING A DELAYED CONTROL SIGNAL TO SAID GATE CIRCUIT INPUT MEANS WHEN SAID LOAD DEVICE IS IN SAID SECOND STATE.
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Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3086109A (en) * 1960-01-18 1963-04-16 Charles G Kaehms Train wheel proximity detector

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3086109A (en) * 1960-01-18 1963-04-16 Charles G Kaehms Train wheel proximity detector

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