US2070900A

US2070900A - Thermionic relay circuit

Info

Publication number: US2070900A
Application number: US619222A
Authority: US
Inventors: Harris Lionel Herbert
Original assignee: Associated Electric Laboratories Inc
Current assignee: Associated Electric Laboratories Inc
Priority date: 1931-07-02
Filing date: 1932-06-25
Publication date: 1937-02-16
Anticipated expiration: 1954-02-16
Also published as: NL215077A

Description

Feb. 16, 1937. L. H. HARRIS 2,070,900

I THERMIONIC RELAY CIRCUIT Filed. June 25, 1932: i *5 She etS Sheet 1 Tm Lionel Hex-LEFT Harris Feb. 16, 1%? L. H. HARRIS THERMIONIC RELAY CIRCUIT Filed June 25, 1932 s Sheets-Sheet 2 IrTen-lw Lionel Herb EFT Harris MK;

@M,17. L H HAJWS mmwo THERMIONIC RELAY C IRCUIT Filed'JLm 25, 1932 3 Sheets-$heet s Lint-1:1 Harbm Harris Patented Feb. 16, .1937

UNITED STATES PATENT OFFICE THERMIONIC RELAY CIRCUIT Lionel Herbert'liarrls, London, England, aasignor to Associated Electric Laboratories, Inc Chicago, 111., a corporation of Delaware Application June 25, 1932, Serial No. 619,222

. In Great Britain July 2, 1931 10 Claims.

The present invention relates to electrical relay apparatus embodying a thermionic valve or a similar electric discharge device for the purpose of producing a change in the direct component of the anode current of such device by the application of a direct or alternating potential to its grid. The chief object of the invention is to provide cheap circuit arrangements whereby a very much greater change in the direct component of the anode current is obtained than hitherto for a given change in applied grid po: 'tential, and moreover this change in the direct component of the anode current is largely insible to secure satisfactory operationof the thermionic relay devices with a high tension source of lower-voltage than would normally be employed; this is particularly advantageous in the case of telephone exchanges where the main op-' erating battery normally employed has a voltage in the neighbourhood of 50 only. which is comparatively low for the "operation of thermionic valves.

According to one feature of the invention in a thermionic relay circuit the anode circuit is ternating current derived from the anode circuit is fed back to the grid thereby increasing the amplitude of the grid swing and changing the direct component of the anode current in consequence of the non-linear characteristic of the valve.

The invention will be better understood from the following description of various methods of carrying it into efl'ect which should be taken in conjunction with the accompanying drawings comprising Figs. 1-9. Fig. 1 shows its applicabe 500, 600, 750 and 900 cycles per second as is the case in systems of this kind already in use.

Referring now to Fig. 1, the transmission line is assumed to extend to the primary of the input transformer ITthe secondary of which is, connected to the thermionic valve V. All the valves shown are of the type having indirectly heated cathodes the heating filaments being connected in series to the exchange battery through a suitable resistance. The valve V acts as an amplifying valve and owing to the fact that the maximum high tension voltage available is that e of the exchange battery, viz. about 50 volts, the output of the valve tends to be limited to a deflnite level irrespective of the strength of the incoming signals. The output of the valve is passed to the transformer T which is a step-down transformer having a large ratio so that the potential difference across the secondary of this transformer is quite small, for instance, less than one volt. As. a further measure tending to preserve the constant nature of the output a fairly low resistance R, for instance of the order of 5 ohms, may be shunted across the secondary of the transformer T. As this low resistance only is common .to the four resonant circuits, interference between them is reduced toa minimum and this makes for high. selectivity. Each of the four receiving circuits is connected in the same manner and as regards the first one it comprises an oscillatory circuit formed of the condenser Cl and the inductance Li in series which is tuned to the particular frequency concerned, say 500 cycles. The junction point of the condenser and inductance is connected by way of the condenser Kl to the grid of the valve VI and the anode circuit of this valve includes the primary of the transformer Tl in series with the signal responding relay RI. -The secondary of the transformer TI is connected across the condenser Kl in series with a rectifier XI while the relay RI is shunted by the condenser Fl which provides a low impedance path for the alternating component of the current inthe anode circuit. It will be understood that each of. the relays RI. R2, R8 and R4 will 'be provided with suitable contacts, for instance one front and one back contact by means of which they will control auxiliary relays which in turn act in combination to give the desired signal.

The operation of the circuit is as follows: When signals are transmitted over the line, they pass to the transformer IT and are extended to the valve V by means of which they are amplified and fed to the transformer T. The output from the secondary of the transformer T which as already explained is largely independent of the input voltages and the load on the transformer is fed to the four tuned circuits in parallel so that the circuits corresponding to the received frequencies at any instant produce relatively high alternating potential at the terminals of the capacities and inductances. The potentials at theterminals oi the inductances are supplied through the condensers KI, K2, K3 or K4 to the grids of the valves VI, V2, V3 or V4 by which they are amplified. The effect of the transformer such as TI is to transfer power back to the grid circuit and the effect of the rectifiers is that the condensers Kl K2, K3 or K3 are charged in such direction as to produce potential of constant sign on the grid so that the current flow in the anode circuit is substantially uni-directional direct current which therefore serves to operate the associated relay.

The change in mean grid potential produced by the condenser charge may also have the effect of increasing the. amplification of the valve by enabling it to work on a steeper part of the grid potential-anode current curve than that to which the valve may normally be adjusted by means of applied grid biasing voltage. If the potential across the tuned inductance is small due to the frequency to which it is tuned being absent from the incoming signal at any instant, with suitable choice of the values of the various components it may be arranged that little or no change occurs in the anode current and thus the necessity for a marginal adjustment of the relays is avoided.

It will be understood that the application of the invention to signalling by means of voice frequency currents of four different frequencies is only given by way of example and that it has numerous other applications some of which will now be briefly referred to. It will be understood that it is not essential that tuned circuits should be employed and the whole of the alternating current input of mixed frequencies may be utilized to operate the receiving relay or similar devices in which case as previously pointed out, greater sensitivity is obtained than if the rectifying arrangement were omitted. Modified-operation may be obtainedby reversing the rectifier and adjusting the grid bias so that sufilcient anode current normally fiows to operate the. relay while on receipt of a signal the effect of the rectifier is to increase the negative potential of the grid so that the anode current falls and with suitable adjustment the relay may then be released. With larger inputs, however, the effect of the rectifier tends to be swamped owing to the amplitude of the signals and it may then be arranged that insufllcient change takes place in the anode current to release the relay.

The two effects just mentioned may each be conveniently combined with resonant or other selective circuits associated with the grid circuit, the anode circuit or the rectifier circuit to give various frequency selecting arrangements. Moreover both eifects maybe used together in conjunction with a tuned circuit, the arrangement being such that if currents of the correct sigfrequency is arranged to increase the negativepotential of the grid and thus reduce the anode current. i

This is illustrated in Fig. 2 in which the selectivity is obtained by a resonant circuit consisting of condenser 2| and inductance 22 in the rectifier circuit. The arrangement is such that due to currents of the correct frequency the condenser 23 is charged by way of the rectifier 24 in one direction and serves to decrease the negative potential of the grid and thus increase the anode current. In response to signals of any frequency, however, -the effect of the rectifier 25 is to charge the condenser 26 in the opposite direction to condenser 23 so as to tend to increase the negative potential of the grid and thus reduce theanode current. This arrangement is such that the values of the impedances of the rectifiers and impedances may be adjusted so that the charge on condenser 23 is greater than that on condenser 26 when signalling current of the frequencies to which the circuit 2l--22 is tuned, while with another frequency the charge on condenser 26 is greater than that on condenser 23. Thus the impedance of circuit 2 l--22 maybe adjusted to be less than that of rectiher 25 and condenser 23 to current of the frequency with which it is desired to operate the relay while the impedance of circuit 2l-24 will, of course, be much greater with currents of other frequencies. Thus when the tuned frequency is received the voltage across 22 will be greater than that across 2 l--22 and with other than the tuned frequency the voltage across 2 |-22 will be greater. Also the values of the impedance of coil 22 and rectifier 25 can'be so adjusted that when both the tuned and untuned frequencies are received, the voltage across 26 through rectifier 25 direct from the transformer obtained from across 2 i- 22 will so nearly equal the voltage across condenser 23 derived from across the'impedan'ce 22 that the grid potential will not be sufllciently changed by the difference in'potential to cause operation of the relay in the anode circuit. Hence-with suitable choice of values it may be arranged that a signal of correct frequency and suificient strength to operate the relay if received alone is unable to produce any operation if mixed with a number of other frequencies. This provides a convenient means for ensuring that a relay which is to be operated by a. signal of a single voice frequency cannot be operated by ordinary speech currents even if they include currents of considerable magnitude of that frequency.

0n the other hand, a circuit without tuning may conveniently be employed to respond to speech currents and this provides an arrangement of greater sensitivity for voice operated relays than those hitherto used. With ordinary speech the conditions obtained will usually vbe that the relay will operate at each accented syllable and consequently if the responding relay is arranged to control a relay provided with a copper slug so as to. be slow to release it is easily arranged that this latter relayzemains operated so long as speech is taking place. Such an arrangement is illustrated in Fig. 3 in which speech currents generated by the microphone 30 are applied to the grid of the valve 3|. by way of the transformer 32 to vary the grid potential. The

aovasco transformer 33 in the anode circuitin response to the variations in the grid potential serves to feed power back to the grid. circuit by way of the rectifier 36 so as to charge the condenser 35 and reduce the negative grid potential as previously described for Fig. 1, thus increasing the sensitivity of the arrangement for operating the relay 36 in the anode circuit. This relay at its contact 31 closes a circuit for the relay 38 provided with a copper slug which due to its slow release characteristics remains energized as long as" conversation continues without a. pause. An adjustable resistance tit serves to vary the grid bias.

One possible application of such an arrangement is to obtain voice supervision on telephone calls, that is to say the operator is signalled owing to the release or the slow relay if no speech takes place over the circuit for a predetermined period. It will be appreciated that only small alterations are necessary to adapt such arrangement for what may be termed volume switching, that is to say the control relay will be adjustedto operate when the input to the device supplied from a microphone reaches a pre-= determined level. The device y also be arranged to test for the presence or tone currents at any point to which it is-oonnected.

As previously mentioned the application of the invention to telegraphy by Morse or other code permits the use of a lower voltage high tension source, or alternatively the use of less components, e. g. fewer valves, or the use of cheaper components, e. g. resonant circuits instead of filters the losses or characteristics incidental to which would. ordinarily preclude their use. An alternative telegraph arrangement may be em ployed in which grid current, flows over the line and is interrupted at the transmitting end in order to send the appropriate signals.

, An arrangement of this type is illustrated in Fig. 4 from which it will be seen that the general arrangement of the circuit follows the same prin= ciples as those already described. 'll represents the operating contact of a Wheatstone tra ter which is shunted by the condenser 62 and it connected across the signalling lines as and M. s5 is the responding relay and t6 the transformer by which feed; back is supplied to the grid circuit by way of a rectifier tl. In this case the valve may be arranged to oscillate so that alternating current from the oscillation of the valve is superimposed on the grid. The alternating potential in the feed-back circuit is applied through the lower adjustable resistance, the rectifier t1, the condenser 62, and over the line to the grid. Due to the rectifying action between thegrid and cathode of the tube a negative potential is accumulated on the grid side of condenser 62. This potential is sufllclently negative to cause the relay to remain at normal. When contact M is closed condenser 42 is discharged and the posi-- tive potential across the upper variable resistance is impressed on the grid. This positive potential causes sufilcient plate current to flow and operate the relay. This arrangementhas been found to work' satisfactorily over very wide ranges of line resistance and also with a comparatively poor line insulation.

The actual circuit details for obtaining what may be called rectified reaction are also capable of considerable modification. For instance as shown in Fig. 5 full wave rectification employing four rectiflers in the'well-known bridge connection' may be employed instead of the halt-wave rectifier arrangement shown in Figs. 1-4. It will be seen that the secondary of the transformer bl in the anode circuit is connected to two opposite corners of the bridge formed by the rectihers 52-55 and the grid circuit is connected across the opposite corners together with a condenser 85. During the positive hall cycle the amplified current in he anode of the tube causes the condenser 56 to assume a positive charge on the grid side by way of 5c and as and during the negative half cycle the condenser SE is charged in the same sense through rectifiers E52 and as.

A modification is shown in Fig. 6 in which a somewhat similar bridge arrangement is used but the bridge consists of the two rectiflers ti and c2 and two condensers 6t and 6 3. This arrangement it will be appreciated gives voltage doubling but otherwise operates in substantially the same manner as previomly described. The amplified current. in the anode circuit of the tube during the positive cycle charges the grid side of'the condenser 5 3 positive through rectifier 62 and during. the negative cycle charges the condenser 53 in the same sense through rectifier iii to double the voltage.

As a further alternative thebias potential provided by rectification of the A. C. component of the anode current may be applied to the grid through a. high leak resistance or the order oi 160,000 ohms instead or by way of a condenser directly connected to the grid. Such an arrangement is shown in Fig. 7 where the output from the teed-back transformer M is applied by way oi. rectifier l2 and high resistance it to the grid of the valve It.

Fig. 8 shows a. further modification in which thetransformer in the anode circuit is dispensed with by making use of a double wound responding relay the second winding of which supplies the feed-back to the grid circuit. Thus the anode current passing through the left-hand winding of the responding relay ill induces corresponding currents in the right-hand winding which are rectified by the rectifier E32 and applied through the secondary of the input transformer to the grid of the valve 53.

A further alternative also dispensing'with a transformer is shown in Fig. 9 in which the coupling-is purely electrical instead of electromagnetic. In this case the input is passed to the transformer 9| the secondary of which is connected to the grid circuit of the valve 82 which has the relay 93 in its anode circuit. A connection from the anode also extends by way of condenser t l to the junction point of the rectiilers 95 and 96 which are connected in the same sense across the further condenser v9'l which in turn is connected to the cathode and the secondary of the input transformer 9| The amplified alternating current at the plate of tube 82 during a positive halt cycle induces a positive charge to flow from the right-hand side of the condenser t1 to the bottom side or condenser 94 through rectifier 96. During the negative half cycle the posicuit for said valve, means including said grid circuit responsive to the receipt of signalling current for generating undulating current in said anode circuit, a plurality of feed-back circuits each including connections directly coupling the grid circuit to its own anode circuit, the first feed-back circuit having means for reducing the mean negative potential of the grid to increase the anode potential in response to signals of a particular frequency, the second feed-back circuit having means for increasing the mean negative potential of the grid to reduce the anode potential in response to signals of different frequencies, and a responding relay connected to said anode circuit operative by said increased potential in the anode circuit only in case said signals are substantially wholly of said particular frequency.

2. In a thermionic relay circuit, a thermionic valve, a grid circuit for said valve, an anode circuit for said valve, means including said grid circuit responsive to receipt of signalling current for generating undulating current in the anode circuit, a plurality of feed-back circuits directly coupling the grid circuit to its own anode circuit, the first feed-back circuit including a rectifier responsive to changes in current in the anode circuitfor applying a uni-directional potential to said gridcircuit to reduce the mean negative grid potential of the grid to in turn increase the anode potential in response to signals of a particular frequency, the second feed-back circuit including a rectifier responsive to changes in current in the anode circuit for applying uni-directional potential to said grid circuit to increase the mean negative potential of the grid to in turn decrease the anode potential in response to signals of different frequencies, and means operative by the increased potential in the anode circuit only in case said signals are substantially wholly of said particular frequency.

3. In a thermionic relay circuit, a thermionic valve, a grid circuit and an anode circuit for said v'alve,a transformer having its primary included in said anode circuit, a tuned circuit including a condenser and a coil resonant to a particular frequency, said tuned circuit shunted across the terminals of the secondary of the transformena first rectifier connecting the point between the coil and condenser of the tuned circuit to the grid, a first condenser connected in shunt of a circuit including said first rectifier and the coil of the tuned circuit in series, a second rectifier and a second condenser in series connected in shunt of said secondary, means including said grid circuit responsive to receipt of signalling current for generating undulating current in the primary in the anode circuit, said first and second condensers charged over their shunt connections in response to changes in current in the primary and secondary of said transformer, the impedances of the tuned circuit and rectifiers being such that on receipt of signals of'only said particular frequency the charge on said first condenser reduces the mean negative grid potential to increase the anode potential while the receipt of different frequencies irrespectiveof whether one of such frequencies is said particular frequency, charges said second condenser to neutralize the charge on the first condenser and to thereby increase the mean negative grid potential to decrease the anode potential.

4. In combination, a thermionic valve including a cathode and an anode, a cathode-anode circuit including a source of current, a responding relay connected in said circuit between the cathode and the anode and responsive to the flow of direct current therein, a grid in said valve for exerting control over the cathode-anode current according to the potential on the grid, circuit connections for maintaining a potential on said grid, means effective when said responding relay is to be caused to respond for superimposing an alternating potential on said grid potential to thereby superimpose an alternating current on the cathode-anode current, a second grid circuit inductively coupled to the cathodeanode circuit to obtain power therefrom when the said alternating current is superimposed on the cathode-anode current, and a rectifying device so connected in the second grid circuit as to produce an alteration of the mean grid potential and cause a consequent alteration of the mean cathode-anode direct current when power is obtained from the cathode-anode circuit, whereby the responding relay is caused to respond to the altered mean cathode-anode direct current.

. 5. In combination, a thermionic valve including a cathode and an anode, a cathode-anode circuit including a source of current, a grid in' said valve for exerting control over the cathode anode current according to the potential on the grid, circuit connections for maintaining a potential on said grid, means effective intermittently for superimposing an alternating potential on said gridpotential to thereby superimpose an alternating currenton the cathode-anode direct current component, a second grid circuit inductively coupled to the cathode-anode circuit to obtain power therefrom when the said alternating current is superimposed on the cathodeanode current, a rectifying device so connected 7 in the said second grid circuit as to produce an alteration of the mean grid potential and a consequent increase of the mean cathode-anode current when power is obtained from the cathodeanode circuit, and a responding relay associated with the cathode-anode circuit and arranged and adapted to respond to the increase of the mean cathode-anode direct current produced as set nating current on the cathode-anode current,

a. second grid circuit inductively coupled to the cathode-anode circuit to obtain power therefrom when the said alternating current is superimposed on the cathode-anode current, said second grid circuit having two branches, means for dividing.

the power obtained from the cathode-anode circuit between the two branches selectively dependent upon the frequency of the alternating current superimposed on the cathode-anode current, a rectifying device connected in one branch of the said second grid circuit so as to produce an alteration in one direction of the mean grid potential and the consequent alteration in one direction of the mean cathode-anode current when amplified power is obtained through such branch from the cathode-anode circuit, and a second rectifying device so connected in the second branch of the second grid circuit as to produce an alteration in the opposite direction of the cathode-anode circuit through the said second branch of the second grid circuit.

7. In combinatioma thermionic valve including a cathode and an anode, a cathode-anode circuit including'a source of current, a grid in said valve for exerting control over the cathodeanode current according to the potential on the grid, circuit connections for maintaining a potential on said grid, means for intermittently superimposing an alternating potential on said grid potential to thereby superimpose an alternating current on the cathode-anode current, a

second grid circuit inductively coupled to the v cathode-anode circuit to obtain power therefrom when the said alternatingcurrent is superimposed'on the cathode-anode current, said second grid circuit having two branches, means for dividing the power obtained from the cathodeanode circuit between the two branches selectively dependent upon the frequency of the in the second branch of the second grid circuit as to produce an alteration in the opposite direction of the mean grid potential anda consequent alteration in the opposite direction of the mean cathode-anode current when power is obtained from the cathode-anode circuit through the said second branch of the second grid circuit, and a responding device associated with the cathodeanode circuit and arranged and adapted so as to respond to an alteration of the mean cathodeanode current only when the alteration is in a given direction from the normal mean value, as

-'controlled through only one of the two said branches of the second grid 0kg.

8. In a thermionic valve circ t arrangement wherein the normal cathode-anode current is maintained by virtue of a normal grid potential,

quenoies on the normal cathode-anode current,

a grid circuit inductively coupled to'the cathodeanode circuit to obtain power therefrom when analternating current is superimposed on the normal cathode-anode current, said grid circuit being composed of two sections, a rectifying ,de-

vice connected in one section so as to produce an alteration in the mean grid potential. in one direction and a consequent alteration of the mean cathode-anode current in one direction responsive to power obtained from the cathode anode circuit over such section of the grid circuit, a rectifier similarly connected in the' other section but in the reversedirection so as to have an opposing effect upon the mean grid potential and consequent opposing eflfect upon the mean cathode-anode current responsive to power obtained from the cathode-anode circuit through the saidsecond section. and means for causing the power in the first section of the said grid circuit to be at a peak responsive to current of substantially a given frequency being superimposed on the cathode-anode current, while the power obtained in the said second section of the .grid circuit is substantially independent of the frequency of the superimposed cathode-anode durrent within wide limits. a

) 9; In combination, a telegraph line incoming to a thermionic valve, a signal-responsive device controlled through the anode-cathode circuit of the valve according to the mean value of the anode-cathode current, a self-oscillating circuit for the valve including the telegraph line, means at the distant end of the telegraph line for opening and closing the self-oscillating circuit to send desired signals over the lineand thereby cause the valve to start oscillating and stop oscillatin according to the desired signals, and means including a rectifier direptly connected to the grid circuit and inductively coupled to the anode-cathode circuit of the valve for causing the mean anode-cathode current to vary according to whether thevalve is oscillating or not, whereby the said signal responding device is enabled to respond according to the desired signals.

10. In combination, a thermionic valve having a cathode, an anode, and a grid, a cathode-anode circuit including a source of current and a responding device operable according to the mean value of the cathode-anode current, means effective when the responding device is to respond for superimposing an alternating current on the cathode-anode current, a pair of rectifiers connected in circuit between the grid of the valve and a source of grid potential, and a connection from a point in the cathode-anode circuit to the junction of said rectifiers including a condenser, whereby alternating current passes from the cathode-anode circuit through the condenser to' the rectifiers-and causes an alteration of the grid potential and a consequent alteration of the mean cathode-anode current so as to bring about a response of said-responding device.

LIONEL HERBERT HARRIS.