US2425734A

US2425734A - Electronic amplifier controlled relay

Info

Publication number: US2425734A
Authority: US
Inventors: Willis H Gille; William J Field; Theodore J Wilson
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1942-11-18
Filing date: 1942-11-18
Publication date: 1947-08-19
Anticipated expiration: 1964-08-19

Description

lg- 19, 1947. w. H. @ILLE Erm. 2,425,734

ELECTRONIC AMPLI-PIER CONTROLLED RELAY Filed Nov. 18, 1942 2 Sheets-Sheet I .eltlllllllllllll WI Au@ 19 1947i w.A H. GILLE Erm. 2,425,734

yELCTRONIG vAMPLIFIER CONTROLLED RELAY Filed Nov. 18, 1942 2 sheets-sheet 2 rag. 1

Wut 4 @fr M Mam Patented Aug. 19, 1947 RELA Willis H. Gille, St. Paul, and William J. Field and Theodore J. Wilson,

a'ssignors Minneapolis, Minn.,

to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a corporation of Delaware Application November 18, 1942, Serial No. 466,009

7 Claims.

l This invention relates to electronic amplifiers, and particularly to amplifiers adapted for use in control systems of the type wherein a device 1s controlled in accordance with an electrical signal produced by means responsive to a controlling condition.

vAn object of the present invention is to provide an improved amplifier circuit for use in a control system wherein it is desired to operate a load device either intermittently for periods ofvarying lengths or continuously, dependert uponthe magnitude of an electrical signal. .Y

Another object of the present invention is to provide an improved amplifier circuit for use in motor control systems of the type shown in the (1o-pending application of Willis H, Gille, Serial No. 447,989, filed June 22, 1942, and in the copending joint application of Willis H. Gille, Albert P. Upton and WilliamA J. Field, Serial No. 466,008, filed November 18, 1942.

A further object of the present invention is to provide an improved amplifier circuit for controlling the operation of a relay in accordance with a variable condition. A still further object is to provide, in such an amplifier, the combination of a circuit operated by the relay and effective to decrease the sensitivityvof the amplifier so as to cause intermittent operation of the relay, and a feedback circuit independent of the relay and effective to increase the sensitivity of the amplifier.

Other objects and advantages of our invention will become apparent from a, consideration of the appended specification, claims and drawing, in which:

Figure 1 is an electrical wiring diagram of an amplifier circuit embodying the principles of our invention,

Figure 2 is a somewhat diagrammatic repre-y sentation of a control system wherein the amplifier circuit of Figure 1 may advantageously be used,

Figure 8 is a graphical representation of the operation of the amplifier circuit of Figure l, and Figure 4 is a graphical representation of the operation of a different portion of the amplifier circuit of Figurey 1.

Referring now to Figure 2, there is shown a, system for controlling the movements of the rudder of an aircraft in accordance with the deflection of a directional gyroscope, diagrammatically indicated at I0, from a normal position. The gyroscope I is constructedJn a manner well known Iin the art, so as to rotate a shaft I Il whenever the aircraft on which the gyroscope is mounted IIS, with which is associated a slider Il.

` M changes its direction. Fixed ont-hc shaft ii is a slider I2, which cooperates with a slidewire resistance i3. The slider I2 and the resistance together form a control potentiometer f4,

vThe resistance I3 is connected in an electrical network I5, of the Wheatstcne bridge type. 'The network I5 also includes a slidewire resistance The resistance I6 and slider il together form a follow-up potentiometer i9. The network I5 is supplied with electrical energy from a transformer secondary winding A54, whose terminals 20 and 2| are connected through conductors 22 and 23, respectively, to the left and right terminals of resistances I3 and I5. The sliders I2 and I1 form the output terminals of the network I5.V

The slider I'I is fixed on. a shaft 24 for rotation therewith. The shaft 24 also carries a pulley 25 and a gear 26. A cable 2l runs over the pulley 25. This cable 21 may be the conventional controlV cable used in aircraft for positioning the rudder. v

The gear 26y engages a pair of gears 30 and 3I, which are fixed on shafts 33 and 32, respectively. The shaft 33 is connectable, through an electrically operable clutch device schematically indicated at 34, to a driving shaft 35. Similarly,

' the shaft 32 is connectable by an electrically operable clutch device schematically indicated at '36 to a driving shaft 31. The

shafts

35 and 31

carry gears

36 and 38, respectively, which mate with each other so that the ,shafts 35 and 3'Irotate in oppo'site directions. The gear 38 operatively engages a gear 4I which is driven by a continuously running motor 42.

The motor 42 may be supplied with electrical energy from any suitable source, as for example a battery 43. An energizing circuit for motor 42 may be traced from the upper terminal of battery 43 through conductors 44 and 4'5, motor 42, a conductor 45, ground connections 41- and 48, and a conductor 48 to the lower terminal of battery43.

The battery 43 also supplies electrical energy to a. converter 5l., which may beof any conventional type, and serves to supply alternating electrical energy to an amplifier 52, which is de scribed in detail in Figure 1. The direct current input circuit for converter 5I may be tracedfrom the upper terminal of battery 43 through conductors 44 and 53,.converter 5I, a. conductor4 54, ground connections 5'5 and 48, and conductor 49 to the lower terminal of battery 43. v.The converter 5I supplies alternating electrical energy through conductors 5i and 51 to power input terminals 58 and 59 of amplifier 52.

The slider |2 is connected through a shielded conductor to an input terminal 62 of amplifier 52. The slider I1, which serves as the other output terminal of network I5, is connected through a conductor 63 to ground at 64. The other input terminal 65 of amplifier l52 is grounded as at 65.

As explained in greater detail hereinafter in connection with the description of Figure 1, the amplifier 52 selectively controls the conductivity of energizing circuits for the electrically operated clutches 34and 36. The energizing circuit for clutch 34 may be traced from the upper terminal of battery 43 through a conductori'60, a terminal 61 of amplifier 52, an internal connection in amplifier 52, a terminal I00, a conductor 69, clutch 34, a conductor 10, ground connections 1| and 4B, and conductor 49 to the lower terminal of battery 43. The energizing circuit for clutch 36 may be traced from the upper terminal of battery 43 through a conductor 13, a terminal 14 of amplifier y52, an internal connection in amplifier 52, a terminal 15, a conductor 15, clutch 36, a conductor 11, ground connections 1-9 and 48, and conductor 49 to the lower terminal of battery 43.

Suitable switch means may be provided for shutting down the entire system when not in use. Also limit switch means may be provided for selectively preventing energization of one or the other of the clutches when the follow-up potentiometer, or the rudder, reaches the end of its range of travel. A suitable switching arrangement is shown, for example, in the Gille application, Serial No. 447,989, dated June 22, 1942, previously mentioned. v

Referring to Figure 1, there are shown the details of the amplifier circuit `52. This amplifier comprises a first preliminary voltage amplification stage 80, a secondvpreliminary voltage amplication stage 8|, and a. final power amplification stage 02. 'I'he amplifier 52 also includes a rectifier circuit 03 for supplying power to the preliminary stages B0 and 8| and to provide suitable biasing potentials for the second stage 0| and the final stage B2.

The first amplification stage 00 includes an electric discharge device, shown as a triode 34, which may be, for example, one half of a twin triode of the type known commercially as type 7F'1. The triode 04 includes an anode 85, a control electrode 86, a cathode 01, and a heater filament 80.

A resistance 90 is connected across the

input terminals

62 and 65 of amplifier 52, so that any signal potential occurring between those terminals causes a corresponding current flow through anode 35, cathode 01, to ground at 93, the ground 'fconnection serving as the negative terminal of he'outputcircuit power supply.

'l'lhesecond' amplifier stage yill includes a tri- -fode'f96 having an anode 91, a control electrode sa, a cathode ss; and a heater niament lon. The

A pair of resistances I I2 and I3 are connected between positive power supply terminal 94 `and ground at ||4. The resistance |I3 is provided with an adjustable tap I I5, and the latter is connected through a. resistance IIS to the lower terminal of resistance |02 in the input circuit of stage 0|. This connection serves to provide a positive bias potential for this input circuit. An additional positive bias potential may be applied to this input circuit through a connection which may be traced from the lower terminal of resistance |02 in the input circuit through a. conductorl |I1. either through conductor Ils, contact ||9, and switch arm |20 to a conductor |24, or through conductor |2|, contact |22 and switch arm |23 to conductor |24, and thence through a variable resistance |25 and a fixed resistance |26 to a conductor in the rectifier circuit 03 which is positive with respect to ground. Variations in the potential of anode 05 caused by variations in the output current of the stage 80 are coupled to the input circuit of stage 0| through a blocking condenser |21 and a conductor |28.

The power amplictaion stage 82 includes a common input circuit for both the triodes |3| and |32. This common input circuit may be traced from either control electrode |34 or control electrode |30 through a conductor |42, a fixed resistance |43, tap |44, a portion of a resistance |45, and ground connections |46 and |41 to cathodes |35 and |39. Variations in the potential of anode 91 caused by variations in the output current of the second amplifier stage 8| are transmitted to the common input circuit of the final stage 82 through a blocking condenser |43 and a-conductor |49 to conductor |42 in the common input circuit. 'I'he resistance |45 is so connected to the rectifier circuit 83 that the tap |44 is negative with respect to ground. The setting of tap |44 with respect to resistance |45 therefore determines a negative bias potential applied to the common input circut of final stage 82, and hence the normal current flow in the output circuits of that stage.

The output circuit of final stage 02 is divided into two branches, each of which includes one of the triodes |3| and |32. Both branches of the output circuit of stage 02 are supplied with alterhating electrical energy from a secondary winding |5| of a transformer |52. The transformer |52 also includes a primary winding |53 and two additional secondary windings |54 and, |55.

From the foregoing, it should be apparent that the two branches of the output circuit ci naal stage 82 may be,conductive on opposite half cycles of the alternating energy supplied by the winding |5|. That is, the triode |3| may oe conductive during -the half cycles when the upper terminal of winding |5| is positive with respect to the center tap |60, while the triode |32 may be conductive during the half cycles when the lower terminalof secondary winding |5| is positive with respect to center, tap |50. The second ary winding |54 of transformer |52 is connected through the terminals 20 and 2| to the network |5 (see Figure 2). Therefore, arly signal which appear-s between the output terminals or network l5 is of the same frequency as the energy supplied to the iiial output stage 02. in accordance with the well known characteristics of alternating current bridge circuits, it will be understood that the timei phase of such a signal depends upon 'the direction of unbalance of the network i5. If the plie se of 'the signal is such that the control electrades |34 and |38 are positive when the upper yterminal'of secondary winding I 5| is positiva'the current flow through triode |3| is increased alcove the normal value determined by the setting of tap |44 on resistance |45, while if the phase of the signal is such that the control electrodes |34 and |38 are positive when the lower terminal of secondary winding |5| is positive, then the current v iiow through the triode |32 is increased.,

Condensers 51 and |63 operate to maintain energization of the relay windings and IGI, respectively, over a period longer than the half cycles during which the triodes associated with the respective relays are conductive. During the half cycle when a particular triode is conductive, the triode supplies the current flowing through the relay winding and .also charges the condenser. During the half cycle when the triode is nonconductive, the condenser discharges through the relay Winding, thereby maintaining the current flow.

Relay |58 includes, in addition to the winding |56, the switch arm |20, previously mentioned,

and a switch arm which cooperates with astationary contact |66', Both the switch arms |20 and |65 are biased by means not shown, to the circuit opening position and are moved to circuit closing position upon sufficient energization of relay winding |56.

The twin diode |10 includes a msn diode nl vhaving an anode |12, a cathode |13, and a heater iilament |14. The second diode is generally indicited at |15, and includes an anode |16, a cathode |11, and a heater filament |18. 'I'he rectifier circuit is of the well known full wave type. On the half cyclesl when the upper ter- .diode M5 to conductor |80. The current supplied to the output circuits of stages 30 and 8| passes from conductor through a filter network comprising a choke coil |8| and condensers |82 and |83 connected between the opposite terminals of the choke coil |8| and ground.4 After passing through the filter network, the current flows along conductor |84 to conductor 94 which serves as the positive power supply terminal for the output circuits ofA stages 80 and 8|. The various ground connections serve as the negative power supply terminal for these output circuits. The current supplied bythe rectifier circuit 83 iiows through the various output circuits and ground connections to ground connection |46, and thence through resistance |45, and conductors |85 and 06 to a center tap |81 on transformer secondary winding 55. it should be noted that the direction. of current iiow through resistance |45 is such as to make its left terminal positive with respect to its right terminal, as indicated =by the legend in the drawing. A filter condenser |88 is connected between conductors |80 and |86.

The heater filaments 88, |00, |36, l40, |14 and |18 may he connected to any suitable source of electrical energy (not shown).

In order to aid those skilled in the art in constructing an amplifier in accordance with our invention, the following table is appended, giving values of the various resistances and condensers used in one embodiment of oury invention:

Quantity 10,000 ohms. M megohm. M megolim. mogohm. 0.1 megolim. .05 mlcrofarad. 500 ohms. .05 microfarad. V4 megohm.

54 megohm. l megohm. y megolim. megohm. 0.1 megolim. .05 microfarad.

.05 megohm.

. .05 microtara l microfarad.

4,000 ohms D. C. resistance; 30 hem-ies inductance.

$5 microfru'ad.A

.05 microtarad.

.05 microiarad.

Operation When the sliders I2 and |1 are in the positions shown in Figure 2, the network |5 is balanced and no signal potential is impressed on the

input terminals

62 and 65 of amplifier 52. Under these conditions, neither of the relays |58 or |62 is energized, and hence neither of the clutches and 36 is energized. The shaft 24, the followup slider I1 and the rudder of the aircraft therefore remain stationary.

In this specification, either of the relay windings |56 or I6I, or either of the relays |56 and |62, may be described as energized whenever the current iiow through the winding in question is sufilcientto move the associated switch arms to, or to hold them in, their attracted position. The windings or relays may be described as deenergized whenever the current flow is such that the switch arms are in their retracted position If the aircraft deflects from the course which it is desired to maintain, the gyroscope I operates the slider I2 across the resistance I3. Let it be assumed that a deflection takes place in a direction such that slider I2 is moved to the left across resistance I 3. Slider I2 thereby assumes a potential nearer `to that of input terminal 2|) than the potential of slider I1. A signal potential is therefore impressed on the input terminals of amplifier 52, and the phase of this signal is the same as that which would be obtained if bridge input terminal 20 were connected to amplifier input terminal 62, and bridge input tcrmina1 2| were connected to ahi; cr input terminal 65. Let it be assumed that the amplifier 52 reacts to a signal of this phase by causing energization of winding |55 of relay |58. Energization of winding |56 causes switch arm |65 to engage contact |66, thereby completing the energizing circuit for clutch 34. It may be assumed that motor 42 rotates in such a direction that when clutch 34 is energized, shaft 24 rotates in a counter-clockwise direction, thereby moving slider I1 to the left along resistance I 6.

As soon as this motion of slider I1 has progressed far enough so that its potential equals that of slider I2, the signal impressed on the input terminals of amplifier 52 is reduced to zero, thereby causing deenergization of clutch 34 and stopping of the shaft 24. y

In a similar manner, it may be observed that if the slider I2 moves to the right from the position shown in the drawing, it thereby attains a potential closer to that of bridge input terminal 2| than that of slider I1. Asignal potential is thereby impressed on the input terminals of amplifier 52. The phase of this signal is the same as that which would be obtained if terminal 2| were connected to amplifier input terminal 62 and terminal 20 were connected to amplifier input terminal 65. This signal is therefore of a phase opposite to that obtained under the conditions Just discussed. This signal causes the amplifier to energize winding I6I of relay |62, thereby causing switch arm |61 to engage contact I 68 and complete the energizing circuit for clutch 36. Energization of clutch. 36 causes shaft 24 to be rotated in a direction opposite to that caused by energization of clutch 34. The shaft 24 therefore moves clockwise, driving the slider I1 to the right along resistance I6 in a direction to rebalance the network I5.

If the shaft 24 is rotating too rapidly as the slider I1 approaches the point at which the network I will be rebalanced, the slider I1 may overshoot the balance point because of the inertia of the moving parts of the system. If such overshooting occurs, a hunting condition is set up, wherein the slider I1 oscillates back and forth about the balance point. In other words, the slider hunts for the balance point without findin'g it. In order to prevent the establishment of such hunting conditions, We have provided means for establishing a range oi' positions extending a short distance on either side ot the balance point, wherein the slider I1 may come to rest, even though the bridge circuit I5 may be slightly unbalanced. This range of positions is known as the "dead spot." Means are provided for adjusting the width of this range of position, and this means is referred to as the dead spot" or sensitivity adjustment. This "dead spot" is of course effective with respect to either the control slider I2 or the follow-up slider I1. We have also provided means for further reducing the tendency of the system to hunt by controlling the average rate of operation of the shaft 21,4 in accordance with the magnitude of the unbalance of the network I5. In our system, if the control slider I2 moves beyond the dead spot, the amplifier circuit causes intermittent energization of one of the clutches I4 and 36, the length of the periods of energization being modulatingly increased as the distance of the slider I2 fromthe dead spot increases, After the slider I2 Ahas passed through a second range of positions, hereinafter referredto as the intermittent range, the particular clutch selected in accordance with the direction of unbalance of the bridge circuit is continuously energized. We have provided in our circuit means for determining the amount of unbalance of the bridge circuit I5 required to cause continuous energization of one of the clutches.

In order to understand the manner in which this operating characteristic of the amplifier and system is obtained, it is necessary first to consider the input potential-output current characteristic of the second amplification stage 8|. This characteristic is completelyv described in detail in the co-pending application of Willis H. Gille, Serial No, 447,989, filed June 22, 1942, previously referred to. Therefore it will be mentioned but briefly in the present application. Referring to Figure 3, there is shown at A the normal input voltage-output current characteristic of the triode 96. Because of the high resistance (1/2 megohm) IIII connected. in series with the control electrode 56, and because the input circuit is biased positively through resistance I I6, tap II5, and resistance IIS, the stage 8| as a Whole does not have the same characteristic as the triode A. The positive biasing voltage causes a current to flow through resistance IDI and from the control electrode tothe cathode in the triode 96. This current, `flowing through resistance IUI, produces thereacross a potential drop which effectively maintains the control electrode 98 at a value only slightly positive with respect to the cathode 99, whenever the resultant voltage impressed on the input circuit at the left terminal of resistance IIII is positive. Therefore, the stage 8| as a whole has an input voltage-output vcurrent characteristic which follows the curve A until a slightly positive value of input potential is reached, after which further increases in the input potential cause no change in the output current. The characteristic of the stage as a whole'therefore follows the curve A when the input potential is negative or just slightly positive, and thereafter abruptly changes and follows the straight line B of Figure 3.

Four different potentials are present on the input circuit of the stage 6I having the characteristic as described above. The first of these four potentials is the biasing potential, which is positive with respect to cathode 99, and whose magnitude is determined by the position of tap II5 with respect to resistance III. In Figure 3,

this positive biasing potential is assumed to have a lmagnitude indicated by the distance C.

The second potential impressed on the input circuit of stage is the alternating signal potential which is transmitted to the input circuit from the output circuit of stage 80 through the blocking condenser |21. For the present discussion of the operation of this system, the signal potential is assumed to have a constant amplitude, as indicated by the curve D in Figure 3. v

By reference to Figure 3, it may be seen that the positive biasing potential C determines the amplitude of the alternating input signal necessary to cause a variation in the output current of stage 8|. Therefore the magnitude of the positive biasing potential C determines the amount of unbalance of bridge circuit I3 necessary to start operation of shaft 24. Hence the adjustment of tap ||5 with respect to resistance ||3 controls the width of the dead spot of the system.

Consider for the moment, the variations in the output current of the stage 8| which would be caused by the signal D acting in conjunction with the biasing voltage C, with no other factors in- `liuencing the operation of the stage 3|. Such variations in output current are illustrated by the curves marked F in Figure 3. The corresponding variations in the input potential and hence in the output current of one of the triodes in the final stage 82, are shown at G in Figure 4. The relays |58 and |62 have the characteristic common to such devices, that a predetermined value of current, which may be that indicated by the line Hin Figure 4, is necessary to cause the relays to move their associated switch arms to their attracted positions, but a smaller value of current is suiiicient to maintain the switch arms 4 in their attracted positions. The minimum value of current which may maintain the relays in their energized condition is indicated by the line K in Figure 4. From an inspection of Figure 4, it may be readily determined that the current values indicated by the loops G are not sufficient to cause energization of the relay.

The third of the four potentials impressed on the input circuit of stage 8| is a unidirectional negative potential developed across resistance |06 and condenser |07 by the current flowing in the final output stage 82, and fed back through resistance |03 and condenser |04 to the input circuit of stage 8|. This potential opposes the positive biasing voltage, and hence tends to increase the sensitivity of the amplifier circuit as the current flowing in the output stage 82 increases. This potential which is hereinafter referred to as the feedback potential is shown at E in Figure 3. This'feedback potential exists at all times when either of the triodes in the output stage 82 is conductive, regardless of whether the current flow through that stage is sufficient to cause operation of either of the relays |58 or |62. It is indicated in Figure 3 that the feedback potential E does not exist until a signal voltage is irnpressed on the input circuit of the nal stage 82, from which it might be inferred that the triodes of the nal stage 32 are biased to cut off. It should be understood that it is not necessary to our invention that the triodes of the final stage 82 be biased to cut off. In fact, they are preferably not biased to cut off. Therefore, the negative feedback voltage will have a small residual value at all times, even when no signal is impressed on.the output stage. This residual value is ineffective in the operationl of our system, since it is opposed by a part of the positive biasing voltage. Both thisresidual feedback voltage and the opposing portion of the positive biasing Voltage have been omitted from-Figure 3 as an aid to the clarity of that figure.

The time constant of the feedback circuit and the inductive effect of the output stage plate circuit cooperate to delay the transmission of the feedback pulse to the input circuit of stage 8| sufficiently so that its effect is not felt until the latter part of the negative swing of the signal voltage during which the feedback pulse is produced. The feedback potential impulse due to the rst cycle of signal D, for instance, appears at El in Figure 3, the second impulse appearing at E2.

During the second cycle of signal D, after the feed-back potential E is effective, the net input potential is represented by the curve L in Figure 3, and has a value determined, by the sum of the magnitudes of the signal potential D and the be noted that in the second cycle the curve N in Figure 4 increases above the line H, and therefore causes energization of the relay and movement of its contacts to their attracted position. The condenser in parallel with the relay winding maintains energization of the relay by maintaining the current flow therethrough as indicated along the dotted line P of Figure 4. It maytherefore be seen that the energization of the relay continues until the current flow therethrough has decreased below the line K, which occurs somewhat more than one cycle 'after the relay is rst energized. l

The fourth of the four potentials impressed on the input circuit of stage 8| is Controlled by the switch arms |20 and |23 of the relays |58 and |52. It may be seen that the movement of either switch arm |20 or |23 into engagement with its associated contact completes a circuit from the input of stage 8| through the resistances |25 and |26 to the conductor` |80, which is connected to the positive terminal of the output voltage supply of stage 8|. This circuit therefore impresses an additional positive potential on the input circuit of stage 8|, which is the fourth potential previously described.

The application of the full value of this fourth potential to the input circuit of stage 8| is dclayed because of the time required to charge condensers |04 and |01 to correspond to the new potential Value maintained across their terminals. The fourth potential applied to the input circuit of stage 0I therefore varies substantially as indicated by the curve Q in Figure 3. This potential introduces an additional component into the curve L which represents the net input potential of the stage 8|. The magnitude of this potential Q is adjustable by variation of the setting of the resistance |25. In the example shown, the magnitude of this potential is sufficient to overcome the influence of the signal D and the negative feedback potential E, and causes the net input potential L to change to a value so that it is no 11 longer effective to cause a variation in the output current of the stage Il. During the third cycle of the signal D, there is therefore no change in the current flow of the output stage l2 and hence the relay becomes deenergized as soon as the curve P passes lbelow the straight line K. If the input signal D becomes sufficiently large as compared with the potential Q, a condition may be obtained wherein the relay will be continuously energized. It may therefore be seen that the adjustment of resistance |25 determines the amount of uri-balance of bridge circuit I5 necessary to cause continuous energization of the relays in the output stage l2.

Movement of tap I along resistance |45 determines the negative biasing potential applied to the input circuit of the final stage 82. If this bias is made increasingly negative, the amount of current obtained from the output stage for a given value of input signal is made smaller, thereby decreasing the sensitivity of the system. On the other hand, increasing this bias in a negative sense decreases that portion of the positive half cycle during which the current flow through the tubeis suilicient to cause operation of the relay. The negative bias therefore has the effect of decreasing the possibility of false operation of one of the relays due to a phase shift in the incoming signal such as may be caused by the fact that the impedances in the bridge and amplifier circuits are not purely resistive. The negative bias also serves to increase the stability of the triodes in the final stage by the introduction of impedance in their input circuits. The tap I should be set to give some compromise value of biasing potential which is experimentally found to give satisfactory sensitivity and at the same time to produce a substantially stable circuit, as far as the phase shift effects are concerned.

It has been shown in the preceding example, that with a signal of a given constant amplitude, the relay selected is energized intermittently for periods having a length of approximately one cycle of the incoming signal. In a circuit using the principles described, it has been found that if the magnitude of the input signal is gradually increased, the periods of energization of the relays increase substantially in steps of one cycle. For example, as the incoming signal is gradually increased from zero, when it reaches approximately the amplitude indicated by the curve D, the selected relay is energized for a period of substantially two cycles, and upon further increase the period of energization increases to a period of substantially three cycles, and so on. It may therefore be said that over a given range of signals, the duration of the periods oi' intermittent energization of the relays is moduiatingly increased in accordance with the value of the signal.

While we have shown and described a preferred embodiment of our invention, other modifications thereof will readily occur to those skilled in the art, and we therefore wish our invention to be limited only by the appended claims.

We Claim:

1. Control apparatus, comprising in combination, relay means including an electrical winding and control means operated thereby upon the occurrence of a current flow through said winding in excess of a predetermined value, electronic amplifier means responsive to an alternating electrical signal potential of variable magnitude for controlling the current now tluusli saisi winding, means including a feedback circuit associated with said amplifier means to increase the sensitivity thereof in accordance with the magnitude of the current flow through said winding. and means effective upon operation of said control means by said winding to decrease the sensitivity of said amplifier'means by an amount greater than the increase produced by said sensitivity-increasing means, and thereby to cause intermittent energization of said winding.

2. Control apparatus, comprising in combina tion, relay means including an electrical winding and control means operated thereby upon the occurrenceV of a current flow through said winding in excess of a predetermined value, electronic amplifier means responsive to an alternating electrical signal potential of variable magnitude for controlling the current flow through said Winding, means including a feedback circuit for applying a unidirectional potential to said amplifier means to increase the sensitivity thereof in accordance with the magnitude of the current iiow through said winding, and means effective upon operation of said control means by said winding to decrease the sensitivity of said ampliiier means by an amount greater than the increase produced by said sensitivity-increasing means, and thereby to cause intermittent energization of said winding.

3. Control apparatus, comprising in combination, means for 'producing an alternating electrical signal potential of variable magnitude, relay means including an electrical winding and switch contacts closable thereby upon the occurrence of a current ow through said winding in excess of a predetermined value, electronic amplitler means responsive to said signal potential for controlling the current flow through said winding, means including a feedback circuit associated with said amplifier means to increase the sensitivity thereof in accordance with the magnitude of the current flow through said winding. and means including a circuit completed by closure of said contacts and effective to decrease the sensitivity of said amplifier means by an amount greater than the increase produced by said sensitivity-increasing means, and thereby to cause intermittent energization of said winding.

4. Control apparatus, comprising in combination, means for producing an alternating electrical signal potential of variable magnitude, relay means including an electrical Winding and con-` trol means operated thereby upon the occurrence of a current iiow through said winding in excess of a predetermined value, electronic amplifier means responsive to said signal potential for controlling the current flow through said winding, circuit means in said amplifier means for controlling the sensitivity thereof in inverse relation to the magnitude of a positive potential applied to said circuit means, feedback circuit means associated with said amplifier means to apply to said circuit means a negative potential varying in accordance with the magnitude of the current flow through said winding, and means effective upon operation of said control means by said winding to apply to said circuit means a positive potential greater than the negative potential applied by said feedback circuit means, and thereby to cause intermittent energization of said winding.

5. Control apparatus, comprising in combination, relay means including an electrical winding and switch contacts closable thereby upon the occurrence of a current flow through an alternating electrical winding in excess of a predetermined value, electronic amplifier means responsive to said signal potential of variable magnitude for controlling the current iiow through said winding, circuit means in said amplifier means for controlling the sensitivity thereof in inverse relation to the magnitude of a positive potential applied to said circuit means, feedback circuit means associated with said amplifier means to apply to said circuit means a positive potential varying in accordance with the magnitudegof the current ow through said winding, and means including a circuit completed by closure of said contacts to apply to said circuit means a positive potential greater than the negative potential applied by said feedback circuit means, and thereby to cause intermittent energization of said Winding.

6. Electrical control apparatus, comprising in combination: means for producing an alternating electrical signal potential of variablemagnitude; a device to be operated in accordance with the magnitude of said signal; electrical Winding means for controlling the operation of said device; electronic amplier means responsive to said signal potential for controlling the flow of current through said Winding means, said ampliiier means including a preliminary stage comprising an electrical discharge ldevice and a later stage comprisingtwo electrical discharge devices connected in phase opposition, each said discharge devicehaving an anode, a cathode, and

a control electrode, an input circuit for each discharge device including its control electrode and cathode, an output circuit for each discharge device including its anode and cathode, the output circuits of said two discharge devices in said later stage having a common portion, an impedance, means connecting said impedance in said common portion so as to produce across said impedance a unidirectional potential substantially proportional to the current owing in said common 14 of saidvamplii'ier means in inverse relation to the magnitude of a positive potential applied to the input circuit of said preliminary stage; feedback circuit means for applying said unidirectional potential to said preliminary stage input circuit with its polarity opposed to said positive potential to increase the sensitivity of said amplifier means; and means for coupling said Winding means to the output circuits of said later stage.

7. Control apparatus, comprising in combination, relay means including an electrical Winding and control means operated thereby upon the occurrence of a current iiow through said winding in excess of a predetermined value, electronic amplifier means responsive to an alternating electrical signal potential of variable magnitude for controlling the current iiow through said winding, means including a `feedback circuit associated with said amplifier means to increase the sensitivity thereof in accordance with the magnitude of the current iioW through said winding, and impedance means in. said feedback circuit eiective to delay said increase in sensitivity for a time substantially equal to one cycle of said signal potential.

WILLIS H. GILLE. WILLIAM J. FIELD. THEODORE J. WILSON.

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

UNITED STATES PATENTS Number Name Date 2,256,304 Wills Sept. 16, 1941 1,742,235 Cooley Jan. '7, 1930 2,109,222 Ryder Feb, 22, 1938 2,040,014 Moseley May 5, 1936 FOREIGN PATENTS Number Country Date 320,705 Great Britain Oct. 24, 1929 Certificate of .Correction Patent No. 2,425,734. August 19, 1947.

WILLIS H. GILLE ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 12, line 75, and column 13, line 1, strike out an alternating electrica and insert instead the Word said; column 13, line 3, strike out said and insert an alternating electrical; and that the said Letters Patent sho uld be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 28th day of September, A. D. 1948.

. [SEAL] 4 THOMAS F. MURPHY,

Assistant Commissioner 0f Patents.

Certificate of .Correction Patent No. 2,425,734. August 19, 1947.

WILLIS H. GILLE ET AL.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 12, line 75, and column 13, line 1, strike out an alternating electrica and insert instead the Word said; column 13, line 3, strike out said and insert an alternating electrical; and that the-said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice.

Signed and sealed this 28th day of September, A. D. 1948.

, [SEAL] 1 THOMAS F. MURPHY,

Assistant Uommz'ssz'oner of Patents.