US2405843A - Signal responsive control system - Google Patents

Description

Aug. 13,1946. E 2,405,843

SIGNAL RESPONSIVE CONTROL SYSTEM Original Filed Nov. 14, 1941 Inventor-z William W. Moe,

Patented Aug. 13, 1946 SIGNAL RESPONSIVE, CONTROL SYSTEM William W. Moe, Stratford, Conn., assignor to General Electric Company, a corporation of New York Original application November 14, 1941, Serial No. 419,223. Divided and this application January 5, 1944, Serial No. 517,097

4 Claims. 1

My invention relates to a signal responsive control system and specifically to an electrical relaying system or keying apparatus the operation of which is eiiected in response to control signals of a predetermined character. This application is a division of my copending applicatlon Serial No. 419,223, filed November 14, 1941, and assigned to the same assignee as the present application.

It is an object of my invention to provide an improved keying system in which a keying operation initiated in response to a control wave of predetermined character is terminated at the end of a definite time interval and the system restored to its initial condition.

It is another object of my invention to provide improved means for restoring a si nal controlled keying system to its initial condition substantially instantaneously at the end of a keying operation so that the system is immediately conditioned to respond to a subsequent control signal.

It is another object of my invention to provide improved pulse generating circuits incorporating means for developing a single, accurately timed pulse in response to a control pulse and also incorporating means for restoring the circuits substantially instantaneously to their initial condition at the end of the pulse.

The features of my invention which are believed to be novel are set forth with particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a circuit diagram of one form of signal responsive device embodying my invention, and Fig. 2 is a circuit diagram of another form of signal responsive device embodying my invention.

Referring now to the drawing, Fig. 1 shows one form of signal responsive device adapted to perform a relaying or keying operation of predetermined time duration, the operation being initiated in response to a unidirectional control pulse supplied from suitable signal receiving apparatus (not shown) and impressed across the input terminals of the apparatus as indicated by conductors Ill. The circuit is arranged to require a predetermined minimum value of control voltage across its input to initiate the control sequence. Furthermore, since the circuit is responsive only to pulses of predetermined duration, shorter pulses even though of greater magnitude,

such as those produced by noise, cannot effect the keying operation. The manner in which these results are achieved will more fully appear from a consideration of the following description relating to the circuits.

Unidirectional control pulses impressed on the conductors ID are supplied between the grid and cathode of a triode amplifier tube II. Anode current normally flows through this amplifier and through a resistor I2 from a suitable power supply represented conventionally by a battery I3. Assume now that a desired control pulse is received which may, for example, be of generally rectangular form as is indicated by the Wave form I4. Also assume that this pulse has a certain time duration, for example, one-half second. This pulse is differentiated to a greater orless degree by a capacitor I5 and resistors I6 and I1 producing a wave at the grid of the device I I generally of the form represented by the wave I8. If the received pulse exceeds a predetermined minimum amplitude, the sharply peaked negative portion P9 of the wave I8 biases the device II suddenly to the condition of anode current cutofi. The device II remains cutofi during a time interval which is practically independent of the duration of the received pulse l4, providing the pulse I4 persists for a predetermined minimum time. This time interval is determined primarily by the constants of the capacitor I5 and resistors I6 and I1. It may, for example, be of the order of .15 second.

A capacitor 20 is connected in shunt to the de-' vice ll. So long as the latter is conducting, a very low impedance discharge path is provided in shunt to the capacitor 29 and the voltage thereacross is maintained at a relatively low value. However, when the triode II is suddenly rendered non-conducting by the received control pulse the capacitor 20 immediately begins to charge through a circuit comprising the source of current I3 and the resistor I2 whereupon the voltage across the capacitor rises at a rate determined by the time constants of this circuit.

A gaseous discharge device 2| of the twoelectrode type, for example, a neon tube, and a resistor 22 are serially connected across the device II and the capacitor 20. The device 2| remains non-conducting until the voltage across the capacitor 20 rises to a predetermined critical value at which it suddenly becomes conductive. This causes a voltage pulse to be developed across the resistor 22 as the capacitor 20 discharges. The constants of the various circuit elements are elected that the time required for the capacitor 23 to charge up to the ignition voltage of the device 2i is somewhat less than the time interval during which the device I i is maintained nonconductive. For example, this charging time may be of the order of .10 second.

It will thus be apparent that unless a pulse is received on the conductors Ill which lasts more than a minimum time interval, i. e., about .10 second in the illustrative example, the gaseous discharge device 2| will not be rendered conductive and no voltage will be developed across the resistor 22. Therefore, a time delay is effectively introduced between the occurrence of a pulse at the terminals ill and the occurrence of a pulse across the resistor 22. The result is that undesired transient impulses lasting less than this predetermined minimum time interval are eiiectively prevented from causing a false operation of the keying or relaying control apparatus 25 now to be described.

The apparatus 25 comprises a pair of electron discharge devices 26 and 2'! represented as triode amplifiers. The anode 23 of the device 23 is connected to the positive terminal, of the potential source 13 through a resistor 23. The anod 33 of the device 2'! is connected directly to the positive terminal of the source l3 by a conductor 3i. Also connected across the source i3 is a voltage divider comprising resistors 32 and 33. The cathodes 34 and 35 of the devices 26 and 2?, respectively, are connected to the junction of the resistors 32 and 33 through a suitable current responsive load device illustrated as the operating coil 33 of a relay. The control grid 3'! of the device 26 is also connected to the junction of the resistors 32 and 33.

The anode 23 of the device 23 is coupled to the control grid 38 of the device 2'! through a capacitor 39. The control. grid 38 is also connected to the grounded negative terminal of the source l3 through a fixed resistor 33 and a variable resistor M in series. The latter two resistors are shunted by a unilaterally conducting device represented as a diode 42 having its cathode 43 connected to the grid 38 and its anode 45 connected to the grounded negative terminal of the power supply source.

The operation and adjustment of the appara tus 25 will now be described. When no control pulse is being received the triode 23 is normally conductive and draws a small anode current, for example, a few hundred microamperes through the resistor 29 and the operating coil 36 of the relay. This current is limited to a low value by the resistor 23. Since the resistor 23 is of high resistance as compared to the resistance of the relay coil 36, the anode 28 is maintained at a relatively low potential with respect to ground. The triode 2'! is normally biased well beyond anode current cutoff by a relatively large potential drop, for example, of the order of 25 to 35 volts, developed across the voltage dividing resistor 33. Therefore, the only current flowing through the relay coil 33 is the relatively small anode current drawn by the triode 26. The relay is so selected that its minimum operating current is well above this value so that it remains in its deenergized position under these conditions.

Assume now that a control wave is received and that a pulse is developed across the resistor 22 as previously described. The upper end of the resistor 22 now suddenly becomes positive and a positive impulse is impressed upon the cathodes 34 and 35 through a coupling capacitor 43. Since the grid 31 is now more negative with respect to the cathode 3d the anode current through the triode 2t suddenly decreases causing the voltage at the anode 2' suddenly to increase. This transient increase in anode voltage is transmitted through the capacitor 38 to the grid 38. The circuit constants are so adjusted that the effective negative bias on the grid 33 is thereby momentarily reduced below the value required t maintain the device 21 biased to cutoff. Anode current now begins to flow through the triode TI. This in turn drivesthe cathode 34 still more positive and the device 23 is rendered completely nonconductive, assuming that the amplitude of the impulse is not alone sufficient to driv device 25 to cutofi. All these transient changes take place very rapidly and cumulatively. The net result is that the applied impulse almost instantaneously causes the triode 26 to be cut off and simultaneously causes the triode 21 to draw a heavy current through the relay coil 36.

The relay now closes a circuit through. its contacts ll. and 4%. This circuit is not shown since these details are not material to the practice of my present invention. It will be appreciated that the closing of the relay can be utilized to effect any desired control operation, for example, it may be utilized to key a radio transmitter or to produce a visible or audible indication that a con trol signal has been received.

Continuing now with the description of the adjustment and operation of the apparatus 25, the triode 23 is maintained biased to cutoff. so lon as the anode current through the triode 2'! and relay 36 exceeds a certain. value determined by the net potential of the grid 33. This potential decreases at a predetermined rate as the capacitor 33 charges through the resistors 43 and 4|. As the capacitor 39 charges, the grid 38 becomes less positive thereby reducing the current in device 2'! and rendering the cathode of device 26 less positive. At the end or" a predeterminedtime interval, the length of which may be adjusted by varying the value of the resistor Al, the positive potential on th cathode ofv device 26 becomes sufliciently reduced to permit the device 26 to begin to draw a small anode current through the resistance 23. The consequent decrease in the potential of the anode 23 is transferred through the capacitor 39 to the grid 38 causing a further decrease in anode current in the triode 2'1. This action is also cumulative since the d crease in anode current through the device. 2 further accelerates the increase in anode current through the device 25. This continues until the capacitor 33 is discharged and the devices 26 and 21 are restored to their initial conditions.

The rate at which the capacitor 39 discharges is caused to be very much faster than its charging rate by reason of the fact that the diode i2 conducts in the direction of discharge current and provides a very low impulse path in shunt to the charging resistors ill and 4!. The circuit is, therefore, substantially instantaneously rethe control impulse; (2) it is maintained opera tive for apredetermined time interval; and (3) it is deenergized substantially instantaneously at the end of this interval. All of these factors contribute toward securing a high degree of stability and reliability of operation.

Fig. 2 represents a slightly different form of the signal responsive apparatus shown in Fig. 1. It is believed that the operation of this apparatus will be readily understood in the light of the foregoing description of Fig. 1. Therefore, it is thought suflicient tocall attention to the particulars wherein the two forms of apparatus diiTer, Corresponding reference numerals have been applied to corresponding elements in the two figures wherever possible.

In the modification of Fig. 2 the coupling capacitor 46 is omitted and the lower end of the resistor 22 is returned to the grid of the device II rather than to ground. This arrangement provides additional protection against false operation. In thi modification, the capacitor 23 discharges through the gaseous discharge device 2| and through the relay coil 38. The resultant impulse developed across the relay coil 36 is impressed upon the grid of the triode II through the resistor 22 in such polarity as to drive the grid positive. This positive impulse opposes the negative control pulse l9 and the triode H is caused to return quickly to its initial conductive state. Consequently, even though the pulse l9 should persist for too long a time interval, the capacitor 20 is prevented from recharging to a value which might otherwise cause a second false tripping of the relay circuit 25.

In the apparatus of Fig. 2 the discharge devices 26 and 21 are conveniently replaced by a single duplex triode 50 having a common cathode 5| for the two sections. This obviously makes no difierence in the operation of the apparatus.

' The voltage dividing resistors 32 and 33 are also omitted in this modification and negative bias forthe grid 38 is provided by a suitable source of direct current indicated conventionally by a battery 52.

In Fig. 2 the diode 42 of Fig. 1 is replaced by a triode 53 having a cathode 54 connected to the upper end of resistor 4!), a control grid 55 connected to the junction between resistor 4| and the source 52 and an anode 55 connected to the grounded negative terminal of the power supply source I3. This triode likewise provides a low impedance discharge path for discharging the capacitor 39. It will be observed that the grid circuit of the device 53 is responsive to the voltages across the resistors 40 and M and that the source 52 also serves as a source of anode current for the triode 53. The triode 53 has some advantages over the diode 42; it is more sensitive to the voltages on the resistors 46 and 4] and provides a discharge circuit for the capacitor 39 around the source 52. If the diode 42 were substituted for the triode 53 in Fig. 2 it is apparent that the discharge current would also have to flow through the impedance of the source 52; however, since the source impedance would generally be low it may be desirable in some cases to make thi substitution.

It will readily be apparent to those skilled in the art that other modifications may be made without departing from the principles of my invention, Therefore, while I have shown particular embodiments of my invention it will be understood that I do not wish to be limited thereto, and I contemplate by the appended claims to cover all modifications which fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A pulse generating system comprising, in combination, a normally conductive electron discharge device having an anode circuit serially including a first and second impedance and a grid circuit including said second impedance, a second electron discharge device having anode and grid circuits both including said second impedance, additional means normally biasing said second device to a non-conductive condition, means for causing the, anode potential of said first device to increase momentarily, means responsive to said potential increase for rendering said second device conductive and said first device non-conductive for a predetermined time interval, said last-mentioned means comprising a capacitor charged from said anode potential through a resistor included in the grid circuit of said second device, said second device being maintained conductive so long as the capacitor charging current exceeds a predetermined value, and means for restoring said devices rapidly to their initial conditions at the end of said interval and for discharging said capacitor, said last means comprising a unilaterally conducting device of low impedance in shunt to said resistor.

2. A keying system for generating a single keying pulse of accurately predetermined time duration in response to a short control impulse comprising, in combination, normally inoperative pulse generating means, means for rendering said pulse generating means operative substantially instantaneously in response to a control impulse, means comprising a capacitance and a charging circuit including a resistance for maintaining said pulse generating means operative for a predetermined time interval, said interval being dependent upon the rate at which said capacitance charges through said resistance, and means for restoring said pulse generating means to its initial condition substantially instantaneously at the end of said interval, said last means comprising a unilaterally conducting device shunting said resistance, said device having very low impedance as compared to said resistance in the direction of discharge current flowing in said circuit.

3. In a system for generating a single keying pulse of accurately predetermined time duration in response to a control impulse of one polarity, first and second thermionic amplifying devices each having respective anode, cathode and control grid electrodes, means connecting said cathodes to a reference point through a common impedance, means connecting said first anode to said point through an anode impedance and an anode current source, means connecting said second anode to said point through an anode current source, means connecting said first anode to said second grid through a capacitor, means connecting said second grid to said point through a resistor, means biasing said grids to maintain said first device normally conductive and said second device normally non-conductive, whereby a predetermined minimum value of current normally flows in said common impedance, means for impressing said control impulse on said first device in a sense to drive said first grid negative whereby said second device is rendered conducting and said first device non-conducting and increased current flows through said common impedance, and a thermionic device having an anode to cathode path connected in shunt to said resistor, said path being poled to have low impedance for current flowing from said point to said capacitor;

4. In a system for generating a single keying pulse of accurately predetermined time duration in response to a control impulse of one polarity, first and second thermionic amplifying devices each having respective anode and cathode and control grid electrodes, means connecting said cathodes to a reference point through a common impedance, means connecting said first anode to said point through an anode impedance and an anode current source, means connecting said second anode to said point through an anode current source, means connecting said first anode to said second grid through a capacitor, means connecting said second grid to said point through a resistor, means biasing said first grid to maintain said first device normally conductive, means including a direct current source having its posi- 8 tive terminal connected to said point for biasing said second grid to maintain said second device normally non-conductive whereby a predetermined minimum value of current normally fiows in said common impedance, means for impressing said control pulse on said first device in a sense to drive said first grid negative whereby said second device is rendered conducting and said first device non-conducting and increased current flows through said common impedance, a third thermionic device having an anode and a cathode and a control electrode, and means connecting said third device across said resistor and said direct current source in series and with said resistor connected between the cathode and grid thereof whereby said third device provides a low impedance path for current flow from said point to said capacitor.

WILLIAM W. MOE.

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