US2433424A - Electronic timing apparatus - Google Patents

Description

Dc- 39 1947. w. H. BRUNS Er Al. 2,433,424

ELECTRONIC TIMINC'I` APPARATUS Filed June 24, 1944 EN ATTORNEY Patented Dec. 30, 11947 UNITED S'llilfllSv 2,433,424

ELECTRONIC TIMING APPARAYIIS William Henry Bruns, Lincolndale, Y., and Harold Edward ('ialanty,` vHillsidef Jaasd sgnors to" Otis Elevator Company, York, N.- Y.Y, av corporation of New Jersey' Application Juncal, 1944, Serial' No'.

1 The invention rclatestc electrical timing ap paratus. especial-ly for eiecting plural timingv operations; I

There are various applications for plural timing in which it is' desired that individual timing operations be consummated inthe saine se; quence as initiating operations. In the copending application of Gavin Watson, William Hen-ry Bruns and Harold Edward Galanty, fil-ed Jurre 24, 1944,.v Serial Number 541,970, for example, calls registered by Vhal-1` buttons 'or an elevator system which. .have remained unanswered for more than a certain. length of' time are given cer-y tainpreference. Inone mode-oi application, preference is given. these callshycausing them to be answered as timed calls inv the order in which the calls were registered.V This involves renderingfonly one of. these calls eecti-ve at a time.

`It is of advantage in electrical timing circuits to employ electronic' tubes', especially grid con-- trolled gas illedtube's. ln'..efecting plural' time ing" operations, 'such as in the Watson et al. application, it is desirable 'to have like apparatus foreach ofv the Various individual timing" operations, so that in. employing electronic tubes, each individual circuit is provi-ded. With-L an electronic tube controlled so that vit may be rendered oonductive after the expirationV of a certain time period; after an initial control operation..

The object of thel invention is toy provide electrical timingapparatus fory plural. timing; oper`ations in whichv each individual. timing 'circuit employs an electronic tube and. in wl'iicli` firing of. the tubes-,is control-'led so that only one tube is conductive at a time and so that the tubes are Vrendered conductive in the order in: which'. control operations for the tubesk areiniti'ated.

In carrying outthe invention,.accor'ding to the arrangement which will. be' described, each individual timing circuit is provided with a condenser which Vis connected across thegrid-- cathode circuit of. the tube.. The condensers are charged to' a voltage value' to preventthe firing ci the tubes. The time'. interval of each indi-- vidual timing circuit is initiated' by acontrol operation which initiates; the discharge of' theY condenser. .The condenser 'discharge is effected' gradually' and. When'.the condenser.-v voltage is re-v duced to a certain value' vthe tube jre's. A reY sistance is' arranged'. in;` the plate circuits of tubes ina feed wire common to the" c'athodes.v When atube fires, thepotentiall dropv across this resistance changes the' potential"` of the? cathodes of the other tubeslwith respect' to grids, to pr'event the.` firing ofthese tubes.. 'Capacitance is 9 Claims'. (Cl. Z50-72)? employed to= delay the decrease of potential drop across this resistance when a tube `ceases *com ducting. This causes the -ri-ng of the' tube the control operation. for which occurred next,l which upon firingv 'blocks the ctiicr tubes as before.y

the'. firir'igof the tubes" inthe order of initiation ci the respective control c.pe'ratici-is` is assured.'

the specific arrangement of circuits illus trated, alternating current voltage isapplied to the plate circuits of the'- tubes to enable the' tubes tev be. shutoit; Also, alternatifigv current voltageis. superimposed cnthef 'condenser' voltage. applied. tothe grid-cathcdefcircuit of each. tube, The phase relationship. or this superimposed grid-- cathode votagewith respect to the plate voltage is such asto tenderthe tulo'e initially conductive near the beginning ci the positiveportion. of a plate" voltage cycle..

Aii'eatures and advantages. of the invention will be seenv from, the following description and apl pended' claims.. f

The flgiire'ot drawing is a Wiring diagram or electrical timing circuits for" a plurality of tim= ing' operations 'in' accordancey with the invention( The circuits are taken from.1"ig1`1re` 4 of the aforementioned depending application of..Wats`on et al. as illustrative'of an application of they invention; In the specific arrangement shown in the Watson et al. application, push .buttons termed hall buttons are arranged at the landings ci. anel'ev'ator system. and act through` floor 11e-f laysv to' control the operation ofY a plurality oielevator cars-.f AnV uphall button aridi a down hall .button lare provided Vat each intermediate landing` and the' downy o'orrelaysthrough the: down hall buttons'. register" calls are pro-r vided witlr contacts to' control the timing appa-f ratus.- Av seven floor-` installation` is shown and; these contacts of the' down: floor relays are provi'd'ed tori thel second', third; tour-th, fth. and. sixth' floors.. The floor. ifelfay'sV for these oors are desig'- nated 3D, .419;'513 ancltD respectively and the particular Vcontactsv dit the floor relays' utilized to control 'the apparatus are designated 3,. this numeral being appended to the' characters employed for.' the-iloor'reiaysfasfor example contacts 2D3 of the down second floor` rc1-ay.

'A source oi direct current-"isprcvided for thev timing'u appar'atus, the supply lines of' which are designated -iif and Certain parts cf the timingy apparatus are individuati tothe' respective floors and 'certain parts 'are 'com-mon toY the* doors; V`It prei-erred to'F arrange most' ofT tlfiisl timing apparatus-asf and' to enclose it'. as' indicated by Y, to seal it against moisture and dirt and to shield it against extraneous electrostatic and electromagnetic effects.

The circuits individual to the respective floors are the same for each floor. Referring for example to the circuits for the second floor, the time interval is obtained by the discharge of a condenser designated ZC. 2R is a discharge resistance for the condenser. The condenser acts through an electronic tube ZCT, hereinafter ree ferred to as a controlled tube. The circuits are particularly adapted for the utilization of a. hot cathode controlled tube which is prevented from firing by a negative grid voltage provided by the charge on condenser ZC, However, other types of controlled tubes may be employed. The anode of the controlled tube is designated ZAN, the cathode ZCA and the grid ZGR. ZSG is a shield grid which is connected to the cathode. tubes without shield grids may be employed. ZIT is a two element tube arranged in the condenser charging circuit and will hereinafter be termed an isolating tube. ZRI is a current limiting resistance in the condenser charging circuit, the purpose of which will be seen as the description proceeds. 2R3 is a resistance in the circuit for the control grid ZGR, the purpose of which will be seen from later description. Contacts 2D 3 on the down second oor relay are provided inthese circuits but are external to the unit Y. These contacts when closed complete an auxiliary discharge circuit for the condenser, this circuit also including the isolating tube ZIT. An electrical load is in the plate circuit' of the controlled tube so that the tube may be connected across the direct current supply lines. This load is illustrated as the coil of an auxiliary time relay ZTR. Connected across the coil of relay ZTR is a condenser ZCZ and resistance ZRZ, the purpose of which will be explained later.r Contacts of the auxiliary time relay are not shown. The corresponding elements of the individual circuits of the unit for the other floors are similarly designated, differentiation being had as to floors by numerals corresponding to floor numbers which precede the designating letters.

As to the circuits common to the various floors, TP is the primary winding of a transformer supplied externally of the unit from a source of alternating current designated AC. TSI, TS2, TS3 and TS4 are secondary windings of this transformer.v Secondary windings TSS and TS4 are for supplying alternating current to the full wave rectier REC. This rectier provides direct current for the charging of condensers 2C to 6C inclusive. Filter condenser C8 and load resistance R8 are connected in parallel across the output supply lines RE-I- and RE- from the rectier. Transformer secondary winding TSZ is utilized to supply current to the heater elements of controlled tubes ZCT to BCT inclusive. For convenience, the heater elements and connections to this secondary winding are not shown.

Alternating current voltage is superimposed on the direct current voltage applied to the plate circuits of the controlled tubes. This superimposed alternating current voltage is provided by transformer secondary winding TSI. The value of this superimposed voltage with respect tothe direct current voltage applied to the plate circuits is such as to cause the resultant voltage applied to the tubes to be negative for a fraction of a cycle. This provides positive voltage for a major portion of the cycle and yet enables the grid of However,

each tube to retain control to shut off the tube.

Combined alternating and direct current voltage is of advantage for the plate circuits in that it enables the use of standard direct current switches in the plate circuits. However, alternating current voltage alone may be applied to the plate circuits. Alternating current voltage provided by transformer secondary winding TSI is also superimposed on the direct current voltage provided by condensers 2C to 6C inclusive in the control grid circuits of the corresponding controlled tubes, Condensers C3 and C4 and resistances R3 and R4 constitute a phase shift network for controlling the phase relationship of the superimposed alternating current grid voltage with respect to the plate voltage.

TC is a manually operable time control switch which acts in conjunction with resistances RI and RZ to effect the common control of the time interval for all individual circuits. R1 is a protective resistance for isolating tubes ZIT to 61T inclusive. Resistance R9 is a loading resistance for the cathodes of the controlled tubes and is arranged in the plate circuits of these tubes on the cathode side in a wire common to the cathodes. Condenser C9 is for delaying the decrease in potential drop across resistance R9 when a controlled tube is shut off. SEI and SEZ are service switches for connecting in the timing apparatus for operation.

When power is applied to lines -land a charge is caused to be built up on condensers ZC to 6C inclusive to cause negative potential to be applied to the control grids of the controlled tubes suilicient to block the tubes. This is eifected by connecting each of the condensers in series with its discharge resistance across resistances R4 and R5. Resistances R4 and R5 in conjunction with resistance R6 constitute a potentiometer resistance connected from line -I- through transformer secondary winding TSI to line As there is no alternating current voltage in secondary winding TSI due to switch SEZ being open, direct current voltage is applied to the condensers. The relative ohmic values of these resistances are such that sucient voltage is applied to the condensers to build up sufcient charge to prevent the firing of any controlled tube, should a floor relay be operated when switches SEI and SEZ are closed, until sufficient time has elapsed to heat up the cathodes. This prevents disintegration of the cathodes. The amount of voltage applied to the condensers is not suicient to cause break-down of the isolating tubes ZIT to 61T inclusive which are connected across the corresponding condensers through resistances ZRI to GRI inclusive respectively and resistances R8 and RI,

Upon the closing of Service switches SEI and SEZ the timing apparatus is rendered effective for operation. The closing of switch SEI shortcircuits resistance R5 to superimpose the alternating current voltage from the phase shift network onto the condenser voltages. The closing of switch SEZ connects the primary winding TP of the transformer to the alternating current source. Secondary windings TS3 and TS4 cause rectifier REC to apply direct current voltage to supply lines RE-land RE-. The value of this voltage is suicient to cause break-down of isolating tubes 21T to 61T inclusive to effect the further charging of the condensers. Taking condenser ZC, for example, as the condenser charge builds up the potential drop across isolating tube ZIT decreases until extinction value is reached whereupon the tube goes out. The condenser then starts to discharge by-way of discharge resistance 2R andY resistance R4 until, due to the lowering of the condenser charge, the voltage `applied to the isolating tube rises t0 a point sucient to break down this tube. This recharges the condenser to a value to cause the isolating tube to .extinguish. This cycle `of operation iscontinuously repeated and may be termed a discharge, recharge cycle.

Before discussing sequence timing, theeffect on an individual timing circuit of-the closing of the corresponding floor relaycontacts will .first be described. For this condition, the eiect Yci resistance R9 `will not be considered. Continuing with condenser 2C as example, upon the closure of contacts 2D3', the auxiliarydischarge circuit for 4thecondenser is completed. This'circuit lis through resistance Rl. At .the same time resistance 2RI is connected across the lines R13-|- andRE-f. Regardless of the point on the oo ndenser discharge, recharge cycle that this occurs the potential drop across the condenser is suiiicient to cause the isolating tube to breakdown. The current flow is in a direction opposite to that for chargingthe condenser and, owing tothe fact that resistance Rl is-of low ohmic value, the condenser discharges immediately to the value of theextinction voltage of the isolating tube. As this pointl is reached, the isolating tube goes out and thecondenser now discharges into discharge resistance 2R and resistance Rd. Owing to the high ohmic value of resistance 2R, this discharge takes place slowly, the rate depending upon the value of this resistance. Should the call be answered and therefore contacts 2D3 separate before the condenser has discharged sufficiently tovreduce the negative potential on the control grid to a point to unblock the tube, the condenser immediately recharges and continues its diS- charge, recharge cycles.

Assume that the ,call is` not answered. and contacts 2D3 do not separate before the condenser has discharged sufciently to reduce the negative potential on grid '2GR with respect to cathode A to a, point to unblock the tube. When this point is reached, the tube res during the positive portion of the next cycle of the voltage applied to the `plate circuit of the tube and continues to conduct `during this Vportion of each` succeeding cycle. The phase relationship of the alternating current Voltage superimposed onthe condenser discharge Voltage with respect to the voltage applied to the plate circuit of the tube is such as to cause the tube to conduct near the beginning .of the positive portion of each cycle of plate voltage. This arrangement causes jthe tube when it becomes conductive to pass suiiicient current to cause operation of relay 2TR, the coil of which is the plate circuit. jUpon the subsequent separation of the cor relay contacts, the condenser is recharged and, upon the potential of the grid becoming negative with respect to the cathode a certain amount, the tube is shut on by the action of the alternating current Voltage applied to the plate circuit. Condenser 2C2 in parallel with the coil of relay ZTR isto obviate the eiTect ofthe inductance of the-coil and thus retain the negative portionof the cycle of applied Voltage. This insures the tube being shut-off when theiioor relay contacts separate. 'Resistance 2R2 serves as a current limitingv resistance for the condenser.

In .order that the Yalcove-:described operations may be .more clearlyunderstood, assume that the direct current voltage of lines -iand is 110 volts, that the peak value of the alternatingcur-y rent voltage superimposed .thereon by trans.-l forrner secondary winding TSI is 1,41 volts, and that indirectly heated .hot cathode controlled tubes having characteristics suitable for these voltages and a critical grid YVoltage of approximately -2 volts are utilized. Also assume that the potential across lines RE`+ and EE- is 180. volts with condenser C8 a 4 microa-rad condenser and with the ohmicvalue of resistance R8 3,000 ohmsand of resistance vRl 1,000 ohms. Assume furtherthat each of condensers 2C to 5C inclusive is a 4 microfarad condenser, that each of resistances 2R. to 6R inclusive is a 20 megohm resistanceand.that the characteristics of veach of isolating tubes 21T to 61T inclusive are such that it breaks down at yy Volts and becomes extinguished at 60 volts. .Assume also that each of resistan-ces 2R! to Viil'ti inclusive is a 30,000 ohm resistance and that each of resistances.2R3 to SRS rinclusive .is a 10,000 ohm resistance. -Assuming that the Vohrnic values of resistances R5 and R5 are .1 and 2 megohms respectively,.when power is applied to lines -I- and condensers 2C to SC inclusive will be charged to 'T3 Volts.

Upon the closure of switches SEE and SE2, alternating current voltage is superimposed on the direct current supply lines and and the voltage of lines RE+ and RE- breaksv down the isolating tubes and further charges the condensers as above described. Referring againto the cir-cuits for condenser 2C for example, upon the voltage drop across the condenser reaching 120 vo1ts,the-voltage drop across isolating tube 21T falls to 60 volts and this tube goes out. -The condenser then starts todischarge through resistance -Due to the high ohmic value of this resistancethe dischargetakes place relativelyslowly. Uponthe lvoltage across the condenser falling to volts the voltage across the isolating tube reaches -85 volts causing the tube to break down. As a result, the condenser immediately recharges whereupon the isolating tube goes out and the Ycondenser discharges again. This discharge, recharge cycle is continuously repeated.

Assume now that contacts 2133 are closed. This may occur at any time during any oneof thecondenser discharge, recharge cycles. The isolating tube is conducting vduring the recharge portion of a cycle and, if the engagement of contacts 2D?, occurs then, the condenser voltage reverses the direction of current iiow in the isolating tube in effecting the condenser discharge by way of the auxiliary discharge circuit. The isolating tube is not conducting during the discharge portion of a cycle so that, should the engagement of contacts 2D3 occur then, the conn denser voltage causes the isolating tube to break down to eiiect the condenser discharge by way of the auxiliary discharge circuit. In either case, owing to the fact that resistance Rl is of low ohmic value, the potential drop across the condenser drops immediately to the extinction voitage or" the isolating tube, namely 60 volts, whereupon the isolating tube goes out. From this point on the condenser discharges slowly into its discharge resistance 2R as before. Upon the separation of contacts 2D3, the condenser is recharged and the discharge, recharge cycles are resumed.

-Inasmuch as upon the engagement of contacts 2133 the condenser voltage falls immediately to the extinction value of the isolating tube, namely 60 volts, a uniform starting point for the timing operation is had, and as the phase relationship of the superimposed alternating current grid voltage with respect to the plate voltage is such as to cause the tube to start to conduct near the beginning of the positive portion of each cycle of voltage applied to the plate circuit, uniform timing intervals are had.

When the controlled tube res, the grid potential becomes positive with respect to the cathode and the negative charge on the condenser is reduced. The values of resistances 2R3 and 2R! are such as to enable, upon the separation of contacts 2D3, the recharging of the condenser to be effected with the result that the tube is shut off when the grid potential becomes 2 volts negative with respect to the cathode. The condenser is recharged to 120 volts and resumes its discharge, recharge cycles. The operation of the timing circuits for each of the other floors is the same.

The length of each timing operation may be varied by varying the value of the phase shift voltage superimposed on the condenser voltage. This is effected by time control switch TC. The position of the time control switch determines the amount of resistance connected in parellel with the right hand portion of resistance R3. In the top position of the time control switch the switch is open, in the next lower position the parallel resistance is Rl of a certain ohmic value, in the next lower position the parallel resistance is R2 of a lower ohmic value, and in the lowermost position the right hand portion of resistance R3 is short circuited. The net result is to decrease the potential drop across the terminals of resistance R3 as the time control switch is moved from its uppermost to its lowermost position, thereby decreasing the value of the phase shift voltage superimposed on the condenser voltage. The lower the value of the phase shift voltage the longer the time interval before a controlled tube is put in condition to conduct. It has been found that, for the characteristics of the circuits and apparatus previously assumed, as to the values of the resistances and condensers of the phase shift network, resistance R3 may be 1750 ohms with the portion to the left of the connection to the time control switch 450 ohms, resistance R4 5,000 ohms, condenser C3 1 microfarad and condenser C4 .25 microfarad. With resistance RI 1,000 ohms and R2 250 ohms, time intervals approximating 1 minute, 1.5 minutes, 2 minutes and 2.5 minutes are obtained in the consecutive positions respectively of the time control switch TC from top to bottom.

Operation when two or more door relays have remained operated for more than a certain length of time will now be described. Under such conditions, resistance RQ becomes effective. The ohmic value of resistance R9 is about one-fifth that of the load in the plate circuit of each tube. Assuming the ohrnic value of the resistance of the coil of each TR relay to be 2,000 ohms, vresistance R9 would be 400 ohms. For such value of resistance R9, a condenser C9 of 250 microfarads would be suitable. When a controlled tube becomes conducting, resistance R9 acts to delay the ring of any other tube, until after' the conducting tube is shut off, while condenser C9 acts to cause the next tube to lire to be the one for which the :door relay has been operated longest. In other words, when a plurality of floor relays have been or become operated for the prescribed period, only one controlled tube can be conductive at a time and the order in rwhich they become conductive is the order in which the floor relays are operated. Resistance R9 and condenser C9 are connected in the common wire leading from line to the cathodes of the controlled tubes. Thus, when floor relay contacts for one floor have been in engagement for the prescribed length of time to cause the corresponding controlled tube to conduct, current flows through cathode loading resistance R9. This raises the potential of the cathodes of all controlled tubes to block all of such tubes except the one which has red.

Assume, for example, that the oor relay contacts iirst engaged for a certain length of time are contacts 2D3. As previously explained, at the expiration of this time period, the negative bias on the control grid of tube 2CT is reduced sufdciently by the condenser discharge to enable the tube to fire. Inasmuch as the plate circuit of tube 2CT is through cathode resistance R9, current flow in this circuit causes a voltage drop across this resistance. As to each of controlled tubes SCT to SCT inclusive, this voltage drop raises the potential of the cathode positive with respect to the control grid. This in effect is the same as increasing the negative bias of the grid with respect to the cathode. This blocks tubes 3CT to BCT inclusive so that should one or more other floor relays lbe operated, in each case when the time interval ewires for the tube controlled by such floor relay, the tube does not fire so long as tube 2CT is conducting. For the voltage values and characteristics previously assumed, the voltage drop across resistance R9 when a tube fires would be about 17 volts which means that the condensers of other circuits for which iloor relay contacts are engaged would have to discharge an additional 17 volts before the tubes controlled thereby could also lire. As this Voltage dilerence exists in the condenser discharge range where the voltage change is relatively slow, the delay in the firing of other tubes is more than ample to insure the answering of the call and consequent separation of the floor relay contacts controlling the tube which is conducting. As to tube 2CT, when it res it immediately drains timing condenser 2C as grid resistance 2R3 is of relatively low ohmic value. Thus, although the cathode potential of tube 2CT is raised in a positive direction, the grid potential is also raised in a positive direction at the same time enabling this tube to continue to conduct.

When contacts 2D3 separate, condenser 2C is recharged, as previously described, to shut oil tube 2CT. If the time interval for another iioor relay has expired, the lowering of the voltage across resistance R9, due to tube 2CT being shut oli, causes the tube controlled by this relay to re, blocking the other tubes. As the time controlled tube 2CT is shut oi should there be more than one floor relay operated, the time interval for each of vwhich has expired, condenser C9 delays the lowering of the potential drop across resistance R9 sufficiently to insure the firing of only the tube controlled by the floor re`ay which has remained operated longest. The delay provided by condenser C9 assures ample time for this controlled tube to ionize and thus re before the difference in potential between the cathode and grid of another tube can become low enough to cause that tube to lire. Thus, it is seen that only one controlled tube can conduct at a time and that the order in which succeeding tubes become conductive is in the order in which the control operations therefor were initiated.

It is contemplated thaty many of the -features of the invention disclosed may be used4 in connection with apparatus and circuits diierent from those specifically described and be applied to systems other than elevator control systems. The timing apparatus, and circuits thereof admit of many variations and many apparently widely ldiierent embodiments of the invention can be made without departure from the spirit and scope of the invention. It is therefore intended that all matter contained in the above description or shown in the accompanying ldrawings shall be interpreted as illustrative and not in a limiting sense,

What is claimed is:

1. Electrical timing apparatus comprising; a plurality of electronic tubes, each having a control grid; means for eac-h tube for impressing gradually changing voltage on the grid-cathode of that tube to cause the tube to become conductive upon such voltage reaching a certain value; and means operable upon any one of said tubes becoming conducting to delay the becoming conductive of other tubes, the votage of said voltage impressing means for which reaches said value while said one tube is conducting.

2. Electrical timing apparatus comprising; a plurality of electronic tubes, each having a control grid; means for each tube for impressing a gradually changing voltage on the gri-d-cathode of that tube to render the tube conductive upon such voltage reaching a certain value; means operable upon any one of said tubes becoming conducting to delay the becoming conductive of other tubes, the voltage of said voltage impressing means for which reaches said value until said one tube is shut-off; and means for causing said tubes to be rendered conductive in the order in Which the voltage of their respective voltage impressing means reached said value.

3. Electrical timing apparatus comprising; a plurality of electronic tubes, each4 having a control grid; means for each tube operable upon the expiration of a certain time interval to apply a potential to the grid-cathode of the tube of a value to cause the tube to re; means for each tube for shutting off the tube; means operable upon the ring of any one of said tubes to delay the firing of other tubes the time intervals for which have expired until after said one tube is shut off; and means operable when the time interval for two or more tubes has expired when a tube which has red is shut oi to cause the next tube to fire to be the one the time interval for which expired first.

4. Electrical timing apparatus comprising; a plurality of electronic tubes, each having a control grid; means for each tube for raising the potential of the grid with respect to cathode of that tube to a value to render the tube conductive; and means operable, upon any one of said tubes becoming conducting, to raise the potential of the cathodes of the other tubes with respect to grids and upon said one tube becoming nonconductive to delay the decrease in said potential of the cathodes with respect to grids of such other tubes.

5. Electrical timing apparatus comprising; a plurality of electronic tubes, each having a control grid; means for each tube for controlling the potential of the grid of that tube with respect to the cathode; a resistance common to said tubes connected so that upon any one of said tubes becoming conducting it provides a potential dropl to raise the potential of the cathodes of the other tubes with respect to grids; and capacitance for delaying the decrease in potential drop" across said resistance upon a tube which has been conducting becoming non-conductive.

6. Electrical timing apparatus comprising; a plurality of gas filled electronic tubes, each having a control grid; means for each tube for controlling the potential of the grid of that tube With respect to the cathode to render the tubes conductive; a conductor common to the plate circuits of the tubes leading to the cathodes of the tubes; a resistance connected in said conductor adapted, upon any one of said tubes becoming conducting,

to provide a potential drop to raise the potential of the cathodes of the other tubes with respect to grids; and capacitance for-delaying the decrease in potential drop across said resistance upon a tube which has been conducting becoming non-conductive.

7. Electrical timing apparatus comprising; a plurality of gas iilled hot cathode electronic tubes, each having a control grid; a condenser for each tube; a discharge resistance for each condenser; means for controlling the charging and discharging of the condensers, the grid-cathode circuit of each tube being connected across the condenser provided for that tube to place a negative potential on the grid with respect to cathode to block the tube when the condenser is charged and to render the tube conducting when the condenser has discharged to a certain voltage value; a resistance common to said tubes connected in the plate circuits of the tubes on the cathode side adapted upon any tube becoming conducting to provide a potential drop to raise the potential of the cathodes of the other tubes with respect to grids; and a condenser connected across said resistance to delay the decrease in potential drop across said resistance upon a tube which has been conducting becoming non-conductive.

8. Electrical timing apparatus comprising; a plurality of gas i'illed hot cathode electronic tubes, each having a control grid; a condenser for each tube; a discharge resistance for each condenser; means for charging the condensers, the gridcathode circuit of each tube being connected across the condenser provided for that tube to place a negative potential on the grid with respect to cathode to block the tube when the condenser is charged and to render the tube conducting when the condenser has discharged to a certain voltage value; a source of current; a plurality of plate circuits, one for each tube, said plate circuits including conductors common to said tubes connected to said source; a plurality of electrical loads, one for each tube, connected in the plate circuits of the respective tubes; a resistance common to said tubes connected in series therewith in that one of said conductors leading to the cathodes of the tubes adapted upon any tube becoming conducting to provide a potential drop to raise the potential of the cathodes of the other tubes with respect to grids to delay any one of them being rendered conductive when the condenser provided therefor discharges to said certain voltage value; and a condenser connected across said resistance to delay the decrease in potential drop across said resistance upon a tube which has been conducting becoming non-conductive to cause, when condensers for two or more Aother tubes have discharged to or kbelow said certain voltage value, that one of such tubes, the condenser for which has been discharging longest, to become conducting.

9. Electrical timing apparatus comprising; a

l1 source of direct current; agas lled electronic tube having a control grid; means for applying direct current voltage from said direct current source to the anode-cathode circuit of the tube; a source of alternating current; means for superimposing alternating current voltage from said alternating current source on said direct current voltage applied to said anode-cathode circuit; a

' condenser connected across the grid-cathode circuit of the tube; means for charging said condenser to place a potential on the grid with respect to the cathode to block the tube; a discharge vresistance connected across said condenser for effecting a delayed decrease in the voltage of said condenser upon discontinuance of the charging thereof; a phase shift network connected to said' alternating current source for superimposing on the voltage applied by said condenser to said gridcathode circuit alternating current voltage of a phase relationship with respect to the Voltage vapplied to said anode-cathode circuit to render the tube initially conductive near the beginning of the positive portion of an anode-cathode voltage cycle upon the condenser discharging to a 12 certain voltage value; and means for varying the value of said superimposed alternating current grid-cathode voltage to vary the time interval from the time the condenser starts to discharge until the tube becomes conductive.

WILLIAM HENRY BRUNS. HAROLD EDWARD GALANTY.

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

UNITED STATES PATENTS

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