US2400069A - Supervisory signaling system - Google Patents

Description

D. w. BLosER ET AL SUPERVISORY SIGNALING SYSTEM Filed Nov. 21, 1942 May 14, 1946.Vv

NLV R EBE O enucdeqd nature can arise.

'usually provided with safety controls which, once "operated, make necessary manual restarting of Patented Mey 14, 1946 /SUPEavisonr 'srGNALmG SYSTEM Dwight W. Bloler, Edgewater, N. J., and Francis C. Evans,

DonganlllllsN Y., assignors to American District Telegraph Company, Jersey City, N. J., a 'corporation of New Jersey Application November 21, 1942, Serial No. 466,516

` 3 claims. (ci. 11m-311) This invention relates to improvements ln supervisory signaling systems and more particularly t such systems especially adapted for use in connectionwith burners, boilers, and the like,

utilizing oil or other fluid fuel. l

In the operation of burners, boilers and the like, as aforesaid, several conditions of a dangerous While such installations are the unit, still the possibility exists that these controls may fail to function and in so doing fail to prevent the existence of such conditions. Should there be a failure of properignition 'of the fuel at an attempted start of operation of the unit, and should the safety controls fail to arrest fuel feed, there would be a strong possibility of a dangerous explosion in the event of a delayed or subsequent ignition of the accumulated fuel in the fire-box. Even more dangerous, however, would be a condition in which ignition and combustion of the fuel failed during unit operation and after the usual starting period, and fuel feed into the hot fire-box cluded in transmission of signals in the event the unit operation is abnormal at the end of a predetermined time interval.

A further object is to provide means whereby the time interval of cyclic operation of the con' trol means preceding transmission of signals can be varied.

Astill furtherobject of the invention is to proi vide means for interrupting the cyclic operation of the control means in the event the unit operation is dnormal whereby transmission of signals is prevented.

was continued. Supervision over the operation of a plurality of installations of this character can be accomplished from a central station if suitable transmitting to that station some code signal denoting the existance of the foregoing and other conditions that require immediate attention. Such attention can be provided by the dispatch of a service attendant from the station. Other conditions at each unit, of which the station can be apprised by code signals, are excessive steam pressure, lack of water or low water, unduly low temperature, and. if desired, supervision of a v still further nature likewise can be carried out.

means be provided at each unit for automatically Accordingly, an object of the inventionis to provide means for causing transmission of code signals in responsive vto abnormal conditions in a unit utilizing oil or other fluid fuel.

Another object of the invention is to provide, in combination with a code transmitter, control means set in operation at each start of unit op-V eration, said control means being operative to cause transmission of code signals in response to abnormal unit conditions and to prevent transmission of signals when u'nit conditions are normal.

Another object of the invention is 'to provide, in combination with a code signal transmitter, control means for the transmitter, said control means being associated with the burner unit in such fashion as to begin a cycle of operation at each starting of the unit, such cycle being c011- 56 'Ihe control means utilized for deenergizing the Another object of the invention is toprovide means whereby code signals are transmitted automatically substantially instantaneously upon the occurrence of certain abnormal conditions of a unit oi.' the type before described.

`An additional object of the invention is to provide means whereby distinctive code signals are transmitted when the safety controls of a unit have operated. or when a power failure of more than a predetermined duration has occurred.

' An ancillary object of the invention is to prov'ide apparatus, associated with the controls of a unit of the type previously described, operative to transmit a codev signal upon the failure of fuel ignition and combustion within a predetermined interval after start of the unit, and also-upon failure of fuel ignition and combustion during a period in which the same must occur as a requisite of successful safe operation.

In carrying out the foregoing and other objects of the invention, it is contemplated that code signaling mechanism can be associated with the normal control system of a fluid fuel unit of the type previously described. To this end, use is made of a code transmitter of well known type adapted to be operated for the transmission of a code signal of one length upon the deenergization of the holding coil of the transmitter and to transmit a code signal of another length upon reenergization of such holding means. The holding means can be deenergized instantaneously upon the occurrence of several abnormalities existent in the operation of the unit and also can be deenergized within a predetermined time interval after the start of operation of the'unit should there be a failure of fuel ignition and combustion. In addition, a second transmitter for code signals can be associated with the system, such transmitter being similar to the first transmitter but being deenergized upon the opening of switches 0f a nature providing certain other supervisory functions.

cam wheel substantially 240.

first transmitter upon failure of fuel ignition and combustion can have the time interval of operation thereof varied as may be desired to t existing circumstances, and operating mechanism is included in this control means for preventing deenergization of the first transmitter upon the ignitlon and proper combustion of fuel within the delay time interval. The component parts of the control means will be described hereinafter in detail as well as the operation of the code transmitters associated therewith.

Other` features, objects, and advantages of the invention will become apparent by reference to the following detailed description of the accompanying drawing, wherein Fig. is a schematic circuit diagram of a supervisory signaling system embodying the invention, and.

Fig. 2 is a representation of the principal part of a transmitter used in this invention.

Referring now to the drawing, i@ indicates generally a code transmitter of weil lrnown type. This transmitter briey described comprises a spring-motor driven rotary wheel li normally held against rotation by a holding coil i2. The wheel Ii has a plurality ofteeth or projections thereon with their path of rotation so disposed relative to a spring contact member id that rotation of the wheel causes intermittent breaking of a circuit, closed by the contact la, in accordiance with the number and spacing of the teeth. This circuit, which includes the lines i5 and i, extends to a central ohice with a second transmitter, indicated generally at il, in series with the first transmitter. The transmitter i 1 is simllar in construction to that previously described, with the exception that a diiferent number of teeth in different spacing maybe employed on the wheel thereof.

These transmitters are of the type in which deenergization of the holding coil I2 releases the wheel I I for rotation and, under the control of suitable cam means, such rotation continues until the wheel has rotated through two complete circuits or rounds, at the completion of which the wheel is locked against further rotation. The cam means is of such nature that, when the coil I2 is reenergized, the wheel is 'released for one circuit or round of rotation. A transmitter of the foregoing type which is welll known to the art has been illustrated representatively in Fig. 2 wherein it will be seen that use is made of e.l pair of holding coils I2 operating an amature t@ having a depending portion 6I at the lower end of which is located a cam follower i. The follower S2 rides in a cam slot 64 cut in a cem wheel 85. The

' outer wall of this slot St has a recess 5 therein and the inner wall likewise has a recess 5'! therein spaced apart in the direction of rotation of the Cam wheel t5 is adapted to be driven by the usual spring motor 68 fastened to the shaft G9 to one end of which is a gear 'IG meshed with a gear 'il on the same shaft with the toothed wheel I I. The ratio of gears 'IB and 'II is approximately three to one so that one complete revolution of cam wheel 55 causes three revolutions of code wheel II. Normally when the coils I2 (one of which would be sufficient) are energized, the cam follower 52 is retained in the recess 66, locking the cam wheel and consequently wheel ll against rotation. When coils l2 are deenergized, the member 6I falls due to gravity, dropping the follower 62 out of the recess 6B into the slot 64, permitting clockwise rotation of the II has made two complete revolutions. Likewise, when the coils I2 are again r'eenergized, the follower is elevated, bearing against the upper wall of the cam slot until recess 66 is again in line wlvh the follower, at which time the follower is moved into this recess, locking the transmitter in normal condition. This latter -arc of movement of approximately 120 results in one complete revolution of the code wheel I I.

Direct current for maintaining the holding coil I2 energized is supplied from a source of direct current, usually a local battery, or its equivalent, indicated by the plus and minus signs, by line 2l, through three switch mechanisms in series, contact Al -of relay A, through the coil I2 to the return line 22. The three switches just mentioned comprise a low water cut-off switch mechanism, a pressure switch mechanism operable to open its contacts upon excessive steam pressure, and a thermostat mechanism adapted to open its contacts when room temperature or the like drops below a predetermined minimum. Devices of this nature are well known and hence have been indicated diagrammatlcally only. Direct current for maintaining the holding coil of transmitter il energized is supplied from the same source through line 2l and through a plurality of supervisory devices through this coil again to the return line 22. These supervisory mechanisms may be of various natures, such as an aquastat, a power phase failure indicator, Aor other equipment of a nature customarily employed in connection with burners of this type.

A direct current circuit can also ce established from the same source through a name detector device, line 24, winding Pf.' of relay B, to the return line 22 for a purpose to be explained later. The dame detector device may be of any' well known character, such as a thermostatic heat detector usually inserted in the stack of the unit.

and utilized with intermittent flame type burners, a stack switch of similar type usually used with intermittent modulated flame type units, a radiant energy detector ordinarily set in an opening in the nre-box or ash pit of the unit, a photoelectronic name detector usually installed in an opening in the fire-box or ash pit of a, unit, or a sensitive thermostatic element designed to be mounted in an opening of the fire-box or ash pit. inasmuch as devices of this character are well known to the art, illustration of any particular one thereof has been omitted, since all operate on the principle of closing a circuit under certain conditions, i. e., satisfactory ignition and combustion of fuel.

'Ilia time delay mechanism utilized in this invention for cooperation with the transmitter IU at the start of operation of a unit and during operation thereof, so far as flame detection. is concerned, is shown as being made up in part of a vacuum tube 25 which has two similar sections SI and S2. Since these sections are similar and each acts independently of the other, they constitute in eiect two separate vacuum tubes in the same glass envelope. The only common element within .this envelope or tube -Zi' is the lament, which can be energized either by a secondary winding 25 of transformer 21 when a supply source of 110 volts A. `C is used, or also energized by winding 26 and the secondary 28 when a 220 volt source is used. In additionto the transformer 21, use is made of a transformer 30, the primary of which is in effect a center-tapped primary with the top part there-A of being used on volt power and the entire primary being used on 220 volt power. In the illustrated equipment I1.10 volt powerA only is used,

though connections have been shown for 220 volt work. Accordingly, the following description and reference to the two transformers will be made on the basis only of 110 voit operation.

The primary of transformer 30 is connected in series with the burner motor M across the power- Asupply line (a source of A. C.) in such a way that the closure of the burner motor starting contacts 3i will shunt the primary of transformer 3l.

Contacts 31 are closed by relay R. which `can be j energized through the secondary of a transformer connected to lthe power supply line through the control thermostat CT which is the thermostat operating a burner unit to control the demand` of tube 25 has such characteristics that the re.

spective grids do not draw-current and consequently, even though a connection is made between the secondary of transformer Scand the condenser 45 of the order of 20 microfarads, and the cathode of section B2. -Between these two circuits is a connecting link, indicated by line 45,

contact 41 of relay B, line 4l, and resistor 40 of' the order of 500 ohms. These two circuits combine to provide the retard or delay period attendant uponl the operationl of transmitter I0 in association with the flame detector.

Due to the connection between the two circuits of section S2, which connection includes the contact 41 of relay B and the resistor 40, the switch 40 and consequently the grid of section S2 are kept essentially at the same potential as the cathgridof section SI, there will be no load on this the point to which is connected the line 35, termed the return wire. The lower end of this plate voltage winding is connected by line 34 tothe two plates of sections SI and S2 of tube 25'. The voltage of that portion of the secondary of transformer 21 in series with the secondary of transformer 30 is opposite in phase to the transformer 30 secondary. The purpose of this arrangement is tov drive the grid of section SI more negative when the voltage applied. by the secondary of transformer 30 is removed. With this secondary voltage of transformer 3l acting between the return wire l5 and the grid in this manner, the grid becomes suniciently positive' on each positive half cycle to permit current to flow through section SI of the tube from plate to cathode.k This current is.sumcient to energize relay B through its lef-t winding BI over a circuit including contact 3l and to charge condenser l1 sufficiently for this condenser to maintain winding Bi in holdingcon-- dition during the negativehalf cycles in which no' current is passed by section/SI. 'I'he condenser 31 may be ofthe order of, say, 40 microfarads.

Windings BI and-B2 of relay B are of additive eilect As before stated, since the two sections of tube 25 are of such character that their grids do not draw current, the result is that the only current existing in the primary of transformer IU is a small magnetizing current-which is of considerably lower value than the current necessary to operate the motor M even if that motor be of the smallest size used in umts of this character. As a further protection, a fuse 24 of value considerably lower than that necessary for the operation of the motor M is provided for protection in the event the primary of transformer $0 should become shorted.

The circuits are connected to the section S2 of tube 25. One of thesey circuits includes an eightpoint switch 40,' a resistor 4l of, say, 600,000 ohms,

ode of this section. The resistors between .the grid and the Switchpoint to which the switch arm 40 may be connected have no effect on the voltage of the grid for the reason, as explained previously, that the grid of Ithis type of tube does not draw current. Consequently, with the grid ofV section S2 maintained at the cathode potential in this manner,A sufficient current flows from the plate to the cathode of section S2 on each positive half cycle of the plate voltage to energize relay A and charge condensers 42 and 45. Condenser discharges on the negative half cycles through the resistor 44 and relay A and, since resistor 44 is of the order of. 15,000 ohms, and condenser 45 is of the order of 20 microfarads, the discharge period thereof is sumciently long to keep relay A from chattering.

Condenser 42 on the negative half cycles discharges through a portion of switch 40 and resistance 4I, the latter resistance. as before mentioned, being in the nature of 600,000 ohms. This resistance is so high, therefore, that the amount of discharge of condenser 42 is negligible. and

- hence it may be assumed that this condenser remains charged. In addition, each section between the taps of switch 40 is of the nature of 50,000

ohms so that, depending on the position of the contact arm 40', the resistance through which condenser 42 can discharge may be increased or decreased, it being understood that the total time necessary for discharge of the condenser may be increased by cutting in additional resistor secbe established whereby the winding BI of relay B can be energized. This circuit extends from the cathode of section SI through the contact A2 of relay A (when relay A is deenergized) line v 5,5, to and through winding BI to return line 35.

a condenser 42 of the order of 40 microfarads, and

the grid of lsection B2. The other circuit includes The use and operation of this supervisory control system in relation to the operation of the burner unit will be described, first. during normal operation of the unit under the heading Normal operation, then under such circumstances of abnormality as result in the transmission of tworound signals under the heading Transmission of two-round signals, next operation of the system under certain circumstances causing transmission of a dierent type of signal under the heading "Transmission of three-round signals," and nnaily in connection with restoration of normal-conditions for certain equipment under the heading Restoration after two-round signals.

Normal Operation petit be assumed that the signaling system is in the condition shown in the drawing wherein relay A, resistor 44l of the order of 15,000 ohms, 75 it will be seen that burner motor contacts 4l are open with the result that potential is applied to the grid of section SI of tube 25, causing energization of winding Bi through the circuit including the contact 33 of this relay. Likewise, the relay A is energized, closingA its contact Ai. Since relay B has one winding Bi energized, it follows that both the contact 33 and the contact 41 will be closed.

When the control thermostat CT of the unit operates to cause starting of operation vof the unit, contacts 3l close, energizing the motor from the source of 110 volts A. C. and shunting theA transformer 30. The secondaryvoltage of transformer 30 immediately drops to zero with the result that positive half cycles of voltage are no longer applied to the grid of section SI of tube 25. Consequently, this section stops `passing current and the winding BI of relay B is deenergized, breaking its own circuit at the contact 33 and likewise breaking the connecting link between the grid and cathode circuits of vsection S2 of tube 25 at contact 4l. When the latter occurs, the voltage on the grid of section S2 does not drop to zero immediately due to the fact that condenser 42 is in a charged state, as previously described. This 'condenser starts discharging through the resistor 4| and such sections of the switch 40 as may be in series therewith, depending on the position of the contact pointer 40.

Since the resistor 4I is of such large value as before described and may have added thereto resistor sections of switch 40, a considerable length of time may be required for full discharge of condenser 42 to take place. As the charge on condenser 42 diminishes, the Ivoltage of the grid more nearly approaches zero and becomes, therefore,'

more negative with respect to the cathode of section S2. This decrease in the voltage on the grid causes a slow reduction in the current passed from the plate to the cathode of section S2 and, if this reduction continues long enough, it will result in the plate-cathode current falling below that value necessary to maintain relay A energized.

However, during this reduction of current passing through relay A, and before relay A. is deenergized, under normal operation the name detector, if ignition is of a satisfactory character, l

gizing relay B and causing both contacts 33 and 4l to close. Closure of contact 41 reestablishes the connecting link between the grid and cathode circuits of section S2, causing the condenser 42 to again become charged and restoring cathode potential to the grid in the manner beforedescribed with the result that full plate cathode current flows through section S2 of tube 25. The timing cycle, determined by the interval necessary for discharge of condenser 42, is interrupted. and the transmitter I0 remains energized, since the plate cathode current through relay- A did not reach such -a low value as to cause this relay to fall back and open contact AI. Consequently, no signals were transmitted by transmitter I0. since the llame detector had operated, indicating normal ignition and combustion.

When the unit control thermostat operates to stop operation of the unit, contacts 3| are opened and transformer 30 immediately reenergized with the result that section SI starts passing current (since contact 33 was closed upon energization of winding B2). Flow of current through section Si again energizes the winding Bi of relay B, creating a condition similar to that existing at the start of operation. After a short time, during which the heat requirement has been satisfied, the flame detector contacts FD will open, thereby opening the circuit to winding B2, but contacts 33 and 41 will remain closed, since winding BI has lbeen energized upon energization of transformer 30. As a result of this operation, the signal system is restored completely to its initial condition and, as before stated, no signals of any type were transmitted.

Transmission of two-round signals intended fashion, then the action described under the heading Normal operation will takel place to the point at which the flame detector contacts FD should close. Under the assumption made, however, that normal ignition did not take place, these contacts would not close, and therefore winding B2 of relay B would not be energized from the local source of DC. As a result of failure4 to energize winding B2, the timing cycle determined by discharge of condenser42 will continue until the grid of section S2 of tube 25 becomes so negative with respect to the cathode of this section thatthe current passed by section S2. is not suiilcient to maintain relay A in such state of energization as to hold contact AI closed. When this state is reached, contact A'I opens instantaneously, breaking the direct current circuit energizing the holding coil I2 of transmitter l0 and, as explained previously, such deenergization of this holding coil immediately releases the wheel Il so that it begins rotation and continues rotation through two complete circuits or rounds, transmitting two rounds o! code signals to the central oillcc. At the same time contact AI opened, contact A2 closed, establishills' the branchv circuit between the cathode of section Si and the return line 35, through winding BI of relay B, but since section SI is not passing current at this time the establishment of this circuit has no effect on winding BI.

Should ignition and combustion ofthe fuel be satisfactory at the beginning of operation of the unit but such ignition and combustion fail prior to the control thermostat reaching its cutoif point without the safety controls operating in their normal fashion, the action of the supervisory signal system will be the same as described under Normal operation up to and including the point at which closure of the flame detector contacts FD energize winding B2 of relay B. When ignition and combustion fail, contacts FD will open, opening the circuit. of winding B2, causing contacts 3l and 41 to again open'evenv though a circuit had been established which ,could energize winding BI but which does not so act due to section Si failing to pass current therethrough. This failure is causedby zero potential on the grid of section Si due to operation of the unit motor. When relay Bi is deenergized as just explained. opening of contact 41 starts the timing, cycle of condenser 42 discharge in the same manner as previously described, and at the expiration of this timing cycle or retard period relay A will be deenergized and transmitter I0 will operate to transmit two rounds of code signais.

In addition to the operation of the system in length of time as is necessary to permit these controls to operate, is then reenergized when the contacts 3| open by action of the safety controls. Whena safety control such as 'a relay for preventing overloading of the ignition transformer operates, the result is to open the motor energizing circuit thereby permitting deenergization of the transformer 30. This same tem- I n porary deenergization of transformer 30 occurs Under these conditionsv cuits of rotation and send twov rounds of code signals. 'This will take place regardless ofthe state of the supervisory control circuit in its association with the flame detector or the manner in which the burner unit is otherwise functioning. y

Similar signals of two-round duration will be transmitted should the control circuit power supplying sections SI 4and S2 of tube 25 fail for a period of several seconds or more. Failure of this power naturally deprives these two sections of current with the result that relays A and B length of time.

will both be deenergized, and upon the opening coil of the transmitter is opened, causing the von a short control power failure. When transformer is deenergized, winding BI of relay B likewise isdeenergized in the manner described under Normal operation, opening its own contacts 33 and 41 and starting the timing or retard' cycle by the opening of the latter. vThe flame detector would not close its contacts, however, if improper ignition and combustion of fuel took place, causing the safety controls to operate, rcenergizing transformer 30. When transformer 30 is reenergized relay B cannot be ener-v gized immediately throughreither one of its coils because its energizing circuits are open at contacts A2 and 33, and also at FD. lConsequently, the timing or retard cycle continues uninterruptedly4 until relay A deenergizes in the manner previously described. When this occurs, contact AI immediately'opens, causing transmitter l0 to .be operated to send two rounds of signals as transmitter to operate for the desired transmission of signals.

All of the conditions described under this heading will cause two-round signals to be sent by the transmitter, and in addition this mechanism is capable of fully supervising itself and its associated wiring-so that two-round signals are transmitted to indicate to the central office the existence of abnormal conditions. In other words, a blown fuse, a defective transformer winding, a burned out tube, a defective relay,

` or transmitter winding, failure of the local source of D. C. supply, or faults occurring in any ofthe external wiring except that between the terminals of the contacts marked FD would immediately result in two-round code signals being transmitted. v A fault occurring in the external wiring to the terminals of the .contacts marked FD would be effective to cause the transmission of this desired signal as soon as the unit started operation, since these contacts are effective only during ignition and combustion of the fuel.

Transmission of three-round signals This signaling system operatesto transmit three rounds of signals in the event the safety controls of the unit function in their normal manner or if the control power (the A. C. source) A failure of fails for from one to five seconds. this control power for less than one seconds duration normally should have no effect on the system, since the condensers 31 and IB are sufiiciently large -to hold charges which can, in discharging.' hold relays Band A energized for that Safety controls may be of various types, illustration of one of which can be found in Schneider Patent No. 2,293,474, issued August 18, 1942, for Control'for automatic heating systems, in which relays are provided to prevent overloading of an oil burner compressor motor or ignition transformer, such relays in turn controlling the energization of another relay l which when deenergized opens the motor circuit.A

Y When the safety controls of the unit operate after start of Vunit operation, the result is that previously described. Simultaneously, contact A2 is closed, completing the circuit .from the cathode of section SI through winding Bl of relay B,

and since this tube is now in condition to pass current, winding BI will be energized, picking up both contactsv of relay B. Closure rof contact 33 in effect shunts the circuit through contact A2 so'vthat relay B will remain energized when contact A2 is opened. Contact 41 in closing restores the connecting link between the grid and cathode circuits of section S2 of tube 25, causing condenser a 42 -again to become charged. While this happens in rapid sequence after relay A first is deenergized, the presence of the resistor 4'9 in the connecting link reduces the charging current to condenser I2 to such an extent that it takes approximately one second for that condenser to charge sufllciently to restore the potential of the grid of section S2 to a value which will permit suiilcient plate cathode current to ow through section S2 and through relay A to energize the same. This delay in recharging of condenser 42, therefore, is of such duration that relay A cannot pick up before transmitter l0 has,l actually started its operation or rotation of wheel ll thereof, and slight creep only of the transmitter without full release thereof, as might occur if relay A picked up too quickly, is prevented. Relay A being againenergized,

closing contact AI, it follows that the holding coil of the 4transmitter I0 is reenergized. However, the transmitter continues its two roundsof rotation oi' wheel Il and then immediately continues through a third round of rotation, "since the arresting cam follower has been movef. from "of an additional round of rotation. This sef ouence or cycle of operation, therefore, causes three rounds of code signals to be transmitted to the central station, indicating clearly to thatv station that the unit is insuch condition as to require manual restarting, since its safety contransformer l0, which is deenergized for such 'It trol circuits or equipment have been operated, or

6 Y that a power iaiiure of shortiduration has occurred, making checking of the unit advisable.

Restoration after two-round signals After a two-round signal has been transmitted to the central oice and the system is subsequently restored to normal, a single round of signals will be transmitted to the central cnice due to the reenergization of the holding coil I2.

Similarly, should either of the three devices in series with the holding coil I2, such as the low water cut-oil, pressure switch, or thermostat, open to cause thetransmission of a two-round signal, closingtv of the same device will reenergize the holdingricoil I2 and cause it thereby to eiect the transmission of a one-round restoration signal.

In addition to the supervision afforded by the devices in series with the holding coil i2, other Services can be rendered by means of the three devices labeled "supervisory devices shown in series with the transmitter IT. While three such members have been shown, it will be apparent that any number may be used. Opening of the contacts of any one of these devices will cause the transmission of a two-round signal by transmitter I, and likewise closing of a once opened device will cause this same transmitter to send its one-round restoration signal.

From the foregoing it will be seen that the present invention providesnovel and efficient means for so supervising the operation of a uid burner unit as to make possible the transmission of` signals to a central ofilce with the signals being of various distinctive characters to indicate approximately to that omce the difiiculty existing at the uiit.\ It will be understood that the invention-is capable of modication beyond the illustrated em limitations to be imposed upon the same are only those set forth in the following claims.

What is claimed is:

1. The combination with a fluid fuel lburner iment, and consequently anyaaoaoee unit of a code signal transmitter, a relay governing said transmitter and holding it inoperative to transmit signals while the relay is energized, a space current path normally energizing said relay, a normally closed link circuit for said space current path, said link circuit being opened by start of operation of said unit, retard means activatedby opening of said link circuit for decreasing current through said space current path and said relay until said relay is deenergized at the end of a predetermined interval to release said transmitter for transmission of signals, and means responsive to successful fuel ignition for closing said link circuit to' arrest decrease of current through said path and said relay prior to deenergization of said relay to prevent transmission of signals.

2. Supervisory means for a fluid fuel burner unit comprising a pair of space current paths, a relay operated by the rst of said paths, a second relay operated by the second of said paths, control means for said second path governed by said first relay, means whereby current flow through said iirst path is interrupted by start of operay tion of said unit causing said control means to interrupt current flow through said second path at the end of a predetermined interval, and a code signal transmitter having a control circuit and a signaling circuit, said transmitter being driven independently of the power energizing said unit and having its control circuit so controlled by said second relay that interruption of current ilow through saidv second path causes transmission of a distinctive code signal.

3. A supervisory system in accordance with claim 2 having a name detector device, means for so connecting said flame detector to said rst relay that operation of said ame detector upon proper fuel ignition energize said first relay thereby toarrest action of said control means prior to the end of said predetermined interval.

DWIGHT W. BLOSER. FRANCIS C. EVANS.

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