US2518380A - Relay circuit - Google Patents

Description

8, 1950 R. G. RQWE EI'AL 2,518,380

RELAY CIRCUIT Filed April 19, 1945 MIN. CONTROL MA X.

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VOLTAGE ATTORNEYS Patented Aug. 8, 1950 UNITED STATES PATENT OFFICE RELAY CIRCUIT Application April 19, 1945, Serial No. 589,152

I 10 Claims. Our inventionrelates to relay circuits and, more particularly, to such circuits using gaseous conductor or thyratron tubes for controlling the energization of a load device or circuit.

As is well known to those versed in the art, gaseous conductor or thyratron tubes'contain essential cathode, grid and anode elements usually in a low pressure atmosphere of mercury vapor, neon, argon and similar gases or combinations thereof. By proper manipulation of electrode potentials and circuit parameters the gas in a given thyratron can be ionized. When the contained gas is ionized the anode-cathode circuit is substantially conducting and the tube is said to be fired. When the contained gas is not ionized the anode-cathode circuit is substantially non-conducting and the tube is said to be extinguished. For convenience, the process or state of being fired can be termed ignition"; the process or state of being extinguished can be termed extinction.

For a thyratron of given characteristics, ignition and extinction may be controlled by the direct current grid voltage for certain combinations of cathode and anode potentials.

However, if direct current is used for the anode supply, the grid loses control after the tube has once fired and it becomes necessary to break the anode supply circuit to extinguish the tube. In

order to permit the grid to retain control over the anode current and extinguish the tube it is common practice to employ alternating current for the anode supply, which eiiectively reduces the anode voltage to zero once during each supply voltage cycle. --Being conductive on only alternate halves of the supply voltage cycle, the tube fires and extinguishes at a rate equal to the supply frequency, and the grid can regain control during periods of extinction.

With circuit parameters adjusted for normal operating conditions with the tube in the extinguished state, the grid-cathode potential which will just fire the tube may be called the ritical ignition potential. With theftube in the fired state, the grid-cathode potential which will just extinguish the tube may be called the critical extinction potential.

Many relay circuits employing thyratrons, both of the gas-triode and gas-tetrode types have been proposed for the switching of heavy-duty, high powered electrical load circuit: by exceedingly small control voltage changes. Some thyratron tubes, in particular those of the hot-cathode gas-tetrode type in typical circuit connections, can be fired and extinguished by as little as 0.05 volt change in control grid bias at exceedingly minute currents. Thus, a power relay or other current responsive electrical load device coupled in the thyratron anode-cathode circuit can be controlled by very small grid bias voltage changes at very low power requirements.

We have found, in fact, that such circuits are often too sensitive to small changes in control grid voltage, In systems in which the control grid bias voltage slowly approaches the critical" ignition or extinction potential, operation of the circuit becomes erratic, unstable and unreliable.

A. further fault in prior art thyratron tube relay circuits is that while they have eliminated some of the disadvantages they have not retained the advantages of the easily controlled sensitivity and the adjustable "pick-up and dropout features of the magneto-mechanical electric relay.

One object of our invention is to provide a thyratron tube relay circuit with improved sta bility, reliability, and resistance to chatter and misfire.

Another object of our invention is to provide a thyratron tube relay circuit with easily variable sensitivity.

A further object of our invention is to provide a simple thyratron tube relay circuit wherein the applied control potential required to fire the tube may be substantially diiferent from that required to extinguish the tube and wherein the difierence in these two potentials is easily, cheaply. and readily controllable.

The novel features which we believe to be characteristic of our invention are engendered with particularity in the appended claims; the invention itself, however, will be best understood by reference to the accompanying description and drawings, in which:

Figure 1 shows a typical thyratron tube relay circuit.

Figure 2 shows the approximate grid voltageplate current characteristic curve of a typical thyratron tube relay circuit.

Figure 3 shows a magnetic-mechanical electric relay circuit.

Figure 4 shows the approximate pick-up and drop out characteristics of a magneto-mechanical electric relay.

Figure 5 shows a thyratron tube relay circuit employing the principles of our invention.

Figure 6 shows the approximate grid voltageplate current characteristic curve of a thyratron tube relay circuit employing the principles of our invention.

With reference to Figure 1, alternating current power supply lines I and 2 supply, through transformer 3, the filament voltage to filament 4 and the anode voltage through the field coil of relay l2 to anode 5 and cathode of thyratron tube 8. Potentiometer II and battery I0, connected as shown to cathode 6 and grid 0, cooperate to represent any source of variable control voltage desired to activate the relay circuit. Such a source, represented by box I6 and terminals II and I3, might be, for example, the voltage drop subtended across an impedance carrying current or the like. Shield grid I of thyratron tube 8 is connected to cathode 6 and is not further essential to a simple description of circuit operation. Filter condenser I is usually essentialto prevent chatter in relay I2 caused by the interrupted unidirectional current flow through tube 8 on only alternate halves of the supply voltage cycle. Power relay contacts i3 and I4 are open when tube 8 is extinguished and closed when tube 8 is fired. For a given combination of filament and anode potentials along with other circuit parameters, the ignition and, extinction of tube 3 and thereby by the condition of relay contacts I3 and I4 is determined by the applied control potential across cathode 6 and grid 9.

For example, using a thyratron tube type number 2050 or a tube having similar characteristics, with 6.3 volts applied to the filament and 115 volts 60 cycle alternating current for the anode supply, circuit parameters can be adjusted so that the tube will fire with approximately 2.05

volts and extinguish with approximately .10

vol-ts negative grid bias, a difference of 0.05 volt.

Figure 2 illustrates the operation of this circuit graphically in a rough approximation. The control voltage is that supplied from control source :8 across terminals ii and I8. With reference to both Figures 1 and 2, this control voltage is equal to the grid voltage of tube 8 applied from grid 9 to cathode 6 regardless of the condition of ignition or extinction of tube 8 because of the low impedance in the circuit. 7

In Figure 2 the solid vertical line represents the critical extinction potential and the dotted vertical line the critical ignition potential. In practice these two potentials do not exactly coincide, but, as shown roughly in the graph, differ by only 0.05 volt. As the applied control voltage is slowly varied from negative 3 volts toward zero volts, for example, the tube will fire at .05 volts. As the applied control voltage is slowly varied from zero toward negative 3 volts, the tube will extinguish at 2.10 volts. However, using slowly varying applied control voltage as is often desirable and as may be produced at terminals I1 and I8 in Figure l, the tube becomes unstable when either the critical firing or extinguishing potentials are approached. Unreliable and erratic operation of the circuit occurs, particularly in the case of slow-varying control voltage.

Figure 3 illustrates a typical magneto-mechanical electric relay M, with field coil terminals 22 and 23 coupled directly to output terminals I! and I8 of control voltage source It and with secondary power contacts 24 and 25 provided for coupling in the power circuit to be controlled.

Figure 4 illustrates graphically the operation of relay 2| and is prepared such that for practical purposes of interpretation the actions of relays and relay circuits in all or the figures shown can be compared. For example, in Figure 2 the solid vertical line represents the circuit control voltage at which thyratron tube 8 will extinguish, whereas in Figure 4 the solid vertical line represents the circuit control voltage at which the armature of magneto-mechanical relay 2| will drop out. In Figure 2 the dotted vertical line represents the circuit control voltage at which thyratron tube 3 will fire, Whereas in Figure 4 the dotted vertical line represents the circuit control voltage at which the armature of magneto-mechanical relay 2i will pick up. Thus, the pick-up and drop ou of the magneto-mechanical relay can be likened to the ignition and extinction of thyratron tube 8, relaying being accomplished in each case by the ability of each device to control high- :1 power secondary loads from control voltages having low power and/or magnitude.

Comparison of Figures 2 and 4 shows that a larger difierence in applied control voltage exists between "pick-up and drop-out of magnetomechanical electric relay 2| than exists between ignition and extinction of the thyratron tube relay. Further, with reference to Figure 3, the difierence between pick-up and drop-out control voltage requirements for relay 2! may be easily controlled within wide limits by simple adjustment of thumb-screw 26 in cooperation with tension spring 21, along with thumb-screw 28 for controlling the initial spacing between armature contact 29 and fixed contact 30. For example, if the initial spacing between armature con tact 29 and fixed contact 30 is increased, the difference in control voltage between pick-up and drop-out increases; if the initial contact spacing is decreased, the diflerence in control voltage decreases. However, in prior art thyratron tube relay circuits no such simple expedient exists for controlling the difference between ignition and extinction control voltages.

With reference now to Figure 5, an illustration of one embodiment of our invention, the circuit and components are identical with those in Figure 1 with the exception that we prefer to employ in addition resistor I9 in series connection with grid 9 and control voltage source terminal H, as well as condenser 20 in shunt with grid 0 and cathode 6 of tube 8. By varying the resistance of resistor I9, which may be a low-priced radio potentiometer or the like, we have found that we can obtain a continuously adjustable difference between the applied control voltage required for ignition and that required for extinction and results closely comparable to those ob tained with the magneto-mechanical relay.

Using the constants and voltages as described in connection with Figure 1, but with the addition of resistor I9 and condenser 20 as described in connection with Figure 5, the following difierences between ignition and extinction control potentials as supplied from source I 6 through terminals [1 and I8 are noted:

. Oong g denser Ignition Extinction ohms 12101,f (11151 voltage voltage None None 2. 05 2. 10 10, 000 1. 0 2. 25 2. 60 15, 000 l. 0 2. 25 3. 40 20, 000 1. 0 2. 25 3. 8O 25, 000 1. 0 2. 25 4, 60 51, 000 1.0 2. 25 -7.40

Further, by following the practice of our present invention, the stability and reliability of prior art thyratron relays can be greatly improved. The circuit containing the disclosed modifications exhibits a locking-in characteristic, which in many applications is extremely desirable, such that once the tube fires or extinguishes small control voltage changes will not disturb the present condition of the circuit. It will be appreciated that by modifications in the values of resistor l9 and condenser 28, smaller difierences between the values of ignition voltage and extinction voltage can be obtained, except as limited by the values with neither resistor l9 nor condenser 20 in the circuit.

At the instant of ignition, a voltage is developed across resistor l9, the magnitude of which is determined in part by the RC combination of resistor is and condenser 26, for eiTecting this diiierence between ignition and extinction control voltage, as measured across terminals l1 and I8, may be accomplished by holding resistor l9 constant while varying the capacity of condenser 20, as shown below:

The polarity of the voltage developed across resistor 19 due to current flow is of a sense such that the negative potential existing from cathode 6 to grid 9 of tube 8 is eiiectively reduced; that is, approaches zero potential when tube 8 fires. This potential drop which appears across resistor iii when tube 8 fires adds algebraically to the applied control potential across terminals ll and I8 and thereby produces the locking-in features characteristic of the present invention resulting in vastly improved stability, reliability and resistance to chatter and misfire. In order for extinction of the tube, the applied control voltage at terminals i1 and [8 must increase in a negative direction until the algebraic sum of the control voltage and the voltage drop across resistor i9 is equal to the actual critical extinction potential. After extinction of thyratron tube 8, the additional voltage appearing across re sistor iii is reduced to substantially zero and the system is automatically and instantaneously recycled for a subsequent operation. In the pressent circuit the grid voltage of tube 8 as measureol from cathode ii to grid 9 is no longer always equal to the applied control voltage. The introduction of resistor Iii, by effectively increasing the impedance of the control source, and the application of condenser 20 to efiectively store the periodic charging voltage during extinction cycles, permits a new voltage component to be automatically produced when tube 8 fires and permits the thyratron relay to function in a novel and desirable manner.

Figure 6 illustrate graphically the nature of the relay characteristics obtainable by practicing the art of the present invention. Comparison with Figure 4 shows how the characteristics of the magneto-mechanical electric relay are simulated. By simple adjustment of variable resistor d, the difference between thecontrol voltage across terminals H and I8 required for ignition and that required for extinction can be controlled from nearly zero to as large a practical value as is desirable.

While we have shown and described in detail a preferred embodiment of our invention, we are aware that it is adaptable to rearrangement and modification without departing from the true spirit and scope thereof. Therefore, we wish it understood that we are not necessarily limiting this invention to the precise embodiment herein disclosed, except in so far as we are limited by the appended claims.

We claim as our invention:

1. A method for controlling a, thyratron gas discharge device having at least two control electrodes, comprising producing a variable control potential by means external to said thyratron, internally producing a potential across said control electrodes by positive ion flow during iterative ignition periods of said thyratron, storing said last-named potential during intervening extinction periods of said thyratron and simultaneously applying said externally-produced control potential and said internally-produced stored potential to said control electrodes.

2. A method for controlling a thyratron gas discharge device having at least two control electrodes, comprising producing a variable control potential by means external to said thyratron, internally producing a potential across said control electrodes by positive ion flow during iterative ignition periods of said thyratron, storing said last-named potential during intervening extinction periods of said thyratron and applying the algebraic sum of said externally-produced control potential and said internally-produced stored potential to said control electrodes.

'3. A method for controlling a thyratron gas discharge device having at least two control elec-= trodes, comprising producing a variable control potential by means external to said thyratron, internally producing a potential cross said control electrodes by positive ion flow during iterative ignition periods of said thyratron, storing said last-named potential during intervenin extinction periods of said thyratron and applying said externally-produced control potential and said internally-produced stored potential simultaneously to said control electrodes, whereby a substantial difierence between the control potential required for ignition and that required for extinction of said thyratron obtains.

4. A method for controlling a, thyratron gas discharge device having at least two control electrodes, comprising producing a variable control potential by means external to said thyratron, internally producing a predetermined potential by positive-ion grid-current flow between said control electrodes during iterative ignition periods of said thyratron, storing a predetermined portion of said last-named potential during inter= vening extinction periods of said thyratron and simultaneously applying said externally-produced control potential and said internally-produced stored potential to said control electrodes, whereby a predetermined difference between the control potential required for ignition and that required for extinction of said thyratron obtains.

5. In a relay circuit comprising a pulsating supply potential, 3, control potential variable by external means, a load and a gasdischarge tube having at least an anode, a cathode and a grid electrode, said last two elements comprising a pair of control electrodes and said supply potential being connected through said anode and cathode to said load; means to produce a substantial difference between the contro otential required for ignition and that required for extinction of said' gas tube circuit. comprising a first connection between one side of said control potential and: one of said control electrodes; a second connection including resistance between the other side of said control potential and the other control electrode and a capacitance connected in shunt with said control electrodes; said resistance means being: limited to suflicientf resistance to produce substantial potential, pulses thereacross by positiveeion grid-current therethrough during. each conducting cycle of said gas tube, and said capacitance: means being limited to sumcient capacitance to store a substantial portion of said ion-current-producedpotential for a time corresponding to at least one half cycle of said pulsating supply potential frequency.

6; A method for controlling a thyratrongas discharge tube. having at least two control electrodes, comprising producing a variable control potential by means external to said thyratron,

internally producing a, potential of adjustable range by positive-ion grid-current flow between said control electrodes during iterative ignition periods of said thyratron,. storing a substantial portion of said last-named potential-during inter'vening extinction periods of said; thyratrc-n and simultaneously applying said externallyproduced control potential: and said internallyproduced stored potential to said control e1ectrodes, whereby anadjustable difference between the control potential required for ignition and that required for extinction of said thyratron obtains.

'7. A method for controlling a thyratron gas discharge tube having at least two control electrodes, comprising. producing a variable control potential by means external to said thyratron, internally producing a potential by positive-ion grid-current flow between said control electrodes during iterative ignition periods of said thyr-atron, storing an adjustable portion of said lastname'd potential during intervening. extinction periods of said thyratron and simultaneously ap-. plying said externally-produced control potential and said internally-produced stored potential to said control electrodes, whereby an'adjustable difference between the control potential required for ignition and that required for extinction 01" said thyratron obtains.

8. In arelay circuit comprising a pulsating supply potential, a control potential variable by external means, a load and a gas discharge device having at least an anode, a cathode and a grid electrode, said last two elements comprising a pair of control electrodes. and said supply potential being connected through. said anode and cathode to saidv load; means to produce a substantial diiference between the control potentialreauired for ignition and that required for extinction of said circuit, comprising resistor means of sufficient resistance to produce substantial po tentialpulses thereacross by positive ion grid current therethrough during each ignition cycle of said gas discharge device, capacitor means of sufiicient capacitance to store a substantial portion of said ion-current-produced potential for a time corresponding to at least one half cycle of said pulsating supply potential, frequency and circuit means arranged to connect said resistor between the control potential and the control electrodes to establish said ion-current potential and to connect said capacitor in shunt with said control electrodes to store said ion-current potential.

9. In a relay circuit. comprising a pulsating;

pair of control electrodes and saidsupply potential being connectedthrough said anode and cathode to said load; a modifying network arranged; to connect said control potential and said control electrodes, including resistance means having sufiicient resistance to; produce substantial potential pulses thereacross by positive ion grid current therethrough, a capacitance means having sufficient capacitance to store a substantial. portion of said ion-current-produced potential for a time corresponding to at least one half cycle of said pulsating'supply potential frequency and circuit means arranged: to connect said re sistance between the control potential and the control electrodes to establish said ion-current potential and to connect said capacitance in shunt with said control electrodes to store said ion-current potential.

10. In a relay circuit comprising a pulsating supply potential, a control potential variable by external means, a load and a gas discharge tube having at least an anode, a cathode and a grid electrode, said last two elements comprising a pair of control electrodes, and saidsupply potential being connected through said anode and cathode tosaid load; a, modifying network arranged to connect said control potential and said control electrodes, including resistance means having sufficient resistance to produce substane tial potential pulses thereacross by positive ion grid current therethrough, capacitance means, having sufiicient capacitance to store a substantial portion of said ion-current-produced potential for a time corresponding to at least one half. cycle of said pulsating supply potential frequency and circuit means arranged to connect said resistance between the control potential and the control electrodes to produce the ion-current potential, to connect said capacitance across the control electrodes to store the ion-current-produced potential and to apply the algebraic sum of said ion-current-produced potential andsaid control potential. to said control electrodes.

' ROBERT G. ROWE.

EDWIN F. ZIEMENDORF.

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

UNITED STATES PATENTS Number Name Date 1,938,742 Demarest Dec. 12, 1933 2,100,460 Specht Nov. 30, 1937 2,114,828 Bedford Apr. 9, 1938 2,132,264 King Oct. 4, 1938 2,190,552 Swart Feb. 13, 1940 2,198,541 Krebs Apr. 23, 1940 2,403,609 Perkins July 9,1946 2,404,001 Smith July 16, 1946 2,420,188 Olving May 6, 1947 FOREIGN PATENTS Number Country Date 443,880 Great Britain May 30, 1934 420,100 Great Britain Nov. 26, 1934 OTHER REFERENCES Gleason: Pulse Response, Proc. of the I. R. Feb. 1946..

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