US2456420A - Electronic direct-current control system - Google Patents

Description

Dem 14, 1948. E. J. JACKSO'NT 2,456, 20

ELECTRONIC DIRECT CURRENT CONTROL SYSTEM Filed Aug. 31, 1946 Inventor: Edwin J. Jackson,

His Attorney Patented Dec. 14, 1948 ELECTRONIC DIRECT-CURRENT CONTROL SYSTEM Edwin J. Jackson, Schenectady, .N. assignor to General Electric Company, a corporation of New York Application August 31, 1946, Serial No. 694,345

4 Claims. 1

This invention relates to control systems, more particularly to electric valve control systems and it has for an object the provision of a simple, reliable, inexpensive and improved control system of this character.

Still more specifically the invention relates to a control system for amplifying a direct signal voltage of either polarity by converting the direct voltage to a square wave periodically varying voltage and amplifier, and a further object of the invention is the provision of a control system of this character which is self-synchronous and which requires no contacts to be driven in synchronism with an A.-C. line voltage.

In carrying the invention into effect in one form thereof, a direct signal voltage is supplied to the input terminals of a vibrator unit having a pair of main vibratory contacts by means of which the signal voltage is chopped and converted into a square wave periodically varying voltage. This voltage is amplified by means of an A.-C. amplifier and the amplified voltage is supplied to the input circuit'of a discriminator stage comprising a pair of electric valves which are connected push pull and each of whichis provided with an anode, a cathode, and a control grid. An auxiliary vibratory contact of the vibrator unit is connected in circuit between the cathodes of the discriminator stage valves and one terminal of the discriminators source of supply. This auxiliary contact is mechanically connected with the main contact of the vibrator unit and is arranged to complete its circuit only in one of the two contact making positions of the main vibratory contact. The voltage at the output terminals of the discriminator stage is uni-directional and its magnitude reverses with reversals in polarity of the direct signal voltage at the input terminals.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawing of which the single figure is a simple, diagrammatical sketch of an embodiment of my invention.

Referring now to the drawing, a vibratory contact unit having stationary contacts la and lb and a vibratory contact lc is provided with input terminals 2 and 3. The vibratory contact I is connected by means of a capacitive coupling to the input circuit of an A.-C. amplifier comprising the electric valve 4 and associated control circuits. This valve is provided with an anode 4a, a cathode 4b, and a control grid 40. It is supplied from a suitable source of direct voltage of which the positive terminal is represented by the conductor 5 and the negative terminal is connected to ground.

;4c and the cathode.

As shown, the anode 4a is connected through the primary winding 6a of a coupling transformer ii to the positive terminal 5 and the cathode is connected to ground. The control grid 40 is connected through the coupling capacitor 1 to the vibratory contactlc. A capacitor 8 is connected between the vibratory contact lo and the cathode 4b, anda resistor 9 is connected between the grid Normally, with no signal voltage applied to the grid 40, the valve 4 is conducting in mid range.

The discriminator stage comprises two electric valves which are preferably included within a single envelope l0. One of the valves comprises the anode Illa, cathode lb and control grid H10 and the other comprises anode Illd, cathode llle and control grid l0]. These valves are preferably connected push pull. As shown, the anodes la and llld are respectively connected through resistors H and i2 to the positive terminal 5a of a source of direct voltage of which the negative terminal is connected to ground. Capacitors l3 and I4 are connected in parallel with resistors II and I2 respectively. Cathodes lllb and llle are connectedby means of a conductor [5 to the negative side of the source. An auxiliary pair of vibratory contacts Ilia and lBb is connected between the cathodes and the negative side of the source. The auxiliary vibratory contact llib is mechanically connected by suitable means to the main vibratory contact lc so that the contacts lb and Mia are made and broken synchronously. Direct voltage for operating the vibrator is supplied to the terminals of the operating coil ltd. A stationary contact lBc cooperates with the vibratory contact lBb to short circuit the coil to provide the vibratory action of the reeds which carry the vibratory contacts.

The grids I00 and H11 of the discriminator stage are connected to opposite terminals of the secto a negative terminal of the source.

ondarywinding 5b of the transformer 6 and the midpoint of the secondary winding is connected A suitable source of a biasing potential is included in this connection. The magnitude of this bias is the valve which is conducting, the voltage drop a sliding contact 20a which is adjusted as nec-I essary to secure a balanced output with zero signal input.

A portion of the output circuit voltage of'the discriminator stage which is obtained from this voltage divider is supplied to the input circuit of a power amplifier which comprises a pair of electric valves connected in push pull. Preferably these electric valves are included within a common envelope 23. These valves are supplied from a source of direct voltage which is preferably the same source as. that from which-the discriminator stage is supplied. As shown, the anodes of the power amplifier stage are connected through coils 24 and .25 to the positive terminal 5a of the source and the cathodes are connected through a resistor 26 to the negative terminal of thesource, Coils 24 and 25 may be the operating coils of relays orthey may be opposed field windl ings of a dynamo-electric machinesuch as a mo- .tor, a generator, or an amplidyne exciter.

Withthe foregoing understanding of the. elements and their organization, the operation'of the system will be readily understood from the following description: It-isassumed that the terminals of the coil-16d of thevibrator are connected to a source of direct voltage and that the vibrator is operating. A signal voltage is i applied to-the input terminals 2 and 3 of which the polarity at the terminal 3 may be assumed to be positive.

Themain vibrator contacts la, lb and lo chop this direct signal voltage into a square wave periodically varying voltage which is amplifled by the amplifier 4. .As a result, a periodi cally varying voltage of the same frequency is .induced in the secondary winding-6b of .the transformer 6. The transformer windings are so poled that the polarity of the voltage. at the lower terminal of the secondary winding is positive when the contact I is in engagement with .the stationary contact lb. and the currentin the primary winding is increasing. At thissame instant, the vibratory contact 161) is in engagement with the stationary contact l6a, thereby completing the cathode circuit of the discriminator stage. The positive voltage of thevlower terminal-of the transformer secondary isiimpressed on the. grid l0] and. consequently current flows from the positive terminal 5a of the source through resistor 42 and from anode [0d to cathode We and thence through conductor l5 and contact 16a tothe negative terminal ofzthe source. As a result of this current flow, a'voltage drop appears across the resistor" oi which the polarity at the center terminal 12a. is positive. This-voltage drop charges the capacitor 14.

During: this same period when contacts a .and I6?) are engaged there is a negative voltage impressed on grid Inc. voltage is less than the critical value above which no plate current can how, current will flow from Sathrough ll, Ina, Illb, |6a and lGb to ground.

.Howevensthe magnitude of this cur-rent will-be .lless than that flowing through resistor I2 andthe If the magnitude of this voltage appearing across II will be less than that across [2.

During the succeeding half cycle the movable contact I0 is in engagement with the stationary contact la. Consequently the polarity of the voltage at the secondary terminals of the transformer is reversed, i. e. the voltage at the upper 7 terminal is positive and the voltage at the lower terminal is negative. However, there is no conduction from the anode l'lla to the cathode lllb because the auxiliary stationary contact lBb is out of engagement with the stationary contact lGa when main contact I0 is in engagement with stationary contact la. During this half cycle in which there is no conduction through either valve of the discriminator stage the voltage drop across the resistor 12 is maintained by the charge on capacitor [4 and the voltage drop across resistor l l is maintained by the charge on capacitor l3. Thus, there is maintained across the resistors If the polarity of the signal voltage is reversed.

the voltage at the lower terminal of the secondstationary contact la.

cathode circuit of the discriminator stage is interupted and'although a positive voltage is applied -to the grid lllf there is no conduction between the cathode lilb and 106. However, during the next half cyclewhen the main vibratory contact I0 is in engagement with the stationary contact lb which is connected to the now negative input terminaL the polarity of the voltage at the upper terminal of the secondary winding 6b is positive.

' During this half cyclethe auxiliary vibratory contact 16b is in engagement with the stationary "contact 16a, thereby completing the cathode circuit of the discriminator stage, and current flows from the positive terminal of the source 5a through resistor l I, and from anode Illa to cathode Nib within the valve and thence by conductor' l5 and by the auxiliary contacts ISa and 46b to the negative terminal of the source. As a result, a voltage drop appears across the resistor ll of which the polarity at the center terminal 1211- is positive and the polarity at the end terminal I la is negative. This voltage drop charges the capacitor I3 so that during the succeeding half cycle, when neither valve of the discriminator stageis conducting, the voltage across the resistor H is maintained.

ing across resistor l2 depending upon the polarity of the D. C.'input voltage and the magnitude of eachvoltage depends upon the magnitude of the l input voltage.

The voltage across resistor H is divided by resistors 1'8, l9 and part of 20 and the voltage acrossresistor I2 is divided by resistors 22, 2| -and part of 20.

These voltages are divided in order to provide'the proper operating grid voltageson grids 23a and 23b. With no signal input on terminals 2 1 23a and 3 the voltages of the grids and 23b are equal and the currents flowing through windings 24 and 25 are equal. With an input signal of the proper polarity i. e. the terminal-"2 positiveand the terminal 3 negative,

the voltage across H increases the current through winding 24 decreases and the voltage across l2 decreases the current through 25 increases. With an input voltage of reversed polarity, the reverse action occurs.

Thus, from the foregoing, it is seen that the magnitude and polarity of the voltage at the output terminals of the discriminator stage corresponds to the magnitude and polarity of the direct signal voltage at the input terminals 2 and 3.

Although in accordance with the provisions of the Patent Statutes this invention is described as embodied in concrete form and the principle thereof has been explained together with the best mode in which it is now contemplated applying that principle, it will be understood that the elements shown and described are merely illustrative and that the invention is not limited thereto since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

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

1. A control system comprising a pair of input terminals adapted to be connected to a source of direct voltage, vibratory contacts with terminals for deriving from said direct voltage a square wave periodically varying voltage, means for amplifying said square wave voltage comprising an electric valve provided with an input circuit connected to said vibratory contacts and an output circuit, a discriminator stage having an output circuit nd having an input circuit connected to the output circuit of said amplifier comprising a pair of electric valves connected push pull and each having an anode, a cathode, and a control grid, connections for energizing said anodes and cathodes from a source of direct voltage, auxiliary vibratory contacts included in said cathode connection, and means for mechanically connecting said auxiliary vibratory contacts with said first mentioned contacts for interrupting and completing said cathode connection synchronously with said square wave voltage thereby to provide a rectified voltage at the terminals of the output circuit having a polarity that reverses with the polarity of the voltage at said input terminals.

2. A control system comprising a vibrator having a pair of input contacts arranged and adapted to be connected to a source of direct voltage, a cooperating vibratory contact, an auxiliary stationary contact and auxiliary vibrating contact cooperating with said auxiliary stationary contact, means for operating said vibratory contacts synchronously, an amplifier comprising an electric valve having an anode, a cathode and a control grid coupled to said first vibratory contact, a discriminator stage comprising a pair of electric valves connected push pull and havin an input circuit coupled to the output circuit of said amplifier stage, an outputcircuit network for said discriminator stage comprising a pair of resistors connected across the anodes of said discriminator stage valves and a separate capacitor connected in parallel with each of said resistors, a connection from an intermediate point of said resistors to the positive terminal of a source of direct voltage and a connection including said auxiliary contacts from the cathodes of said discriminator stage valves to the opposite terminals of said source for increasing the conductivity of one of said discriminator stage valves for one polarity of said input voltage and for increasing the conductivity of the other of said discriminator stage valves for the opposite polarity of said input voltage.

3. A control system comprising a discriminator stage having an input circuit and an output circuit and comprising a pair of push pull connected electric valves each provided with an anode, a cathode and a control grid, 3, pair of input terminals adapted and arranged to be connected to a source of direct voltage, vibratory contacts connected to said terminals for deriving from said direct voltage a square wave periodically varying voltage, an electric valve alternating current amplifier for amplifying said square wave voltage and supplying the amplified voltage to said input circuit, connections from the anodes and cathodes of said discriminator valves to a source of direct voltage for energizing said push pull valve, an auxiliary pair of vibratory contacts included in said cathode connection, and means mechanically connecting said auxiliary contacts with said first mentioned contacts for interrupting and completing said cathode connection in synchronism with said square wave voltage for selectively rendering said discriminator valves conducting thereby to provide at the terminals of said output circuit a uni-directional voltage varying in polarity with the polarity of the voltage at said input terminals.

4. A control system comprising a discriminator stage having an input circuit and an output circuit and comprising a pair of push pull connected electric valves each provided with an anode, a cathode and a control grid, a pair of input terminals adapted and arranged to be connected to a source of direct voltage, vibratory contacts connected to said terminls for deriving from Said direct voltage a square wave periodically varying voltage, an electric valve alternating current amplifier for amplifying said square wave voltage and supplying the amplified voltage to said input circuit, connections for energizing the anodes and cathodes of said discriminator valves from a source of direct voltage, an auxiliary pair of vibratory contacts included in said cathode connection, means mechanically connecting said auxiliary contacts with said first mentioned contacts for interrupting and completing said cathode connection in synchronism with said square wave voltage for selectively rendering said discriminator valves conducting thereby to provide at the terminals of said output circuit a uni-d:irectional voltage varying in polarity with the polarity of the voltage at said input terminals, a power amplifier stage having an input circuit and an output circuit divided into two portions comprising a pair of electric valves connected push pull and having its input circuit connected to the output circuit of said discriminator stage, and a pair of electromagnetic devices having coil windings connected differentially in said portions of said output circuit.

EDWIN J. JACKSON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,297,543 Eberhardt Sept. 29, 1942 2,323,966 Artzt July 13, 1943 2,413,788 Sergeant Jan. 7, 1947

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