US3254331A

US3254331A - Alarm annunciator with independent acknowledgement indication

Info

Publication number: US3254331A
Application number: US238867A
Authority: US
Inventors: Edward S Ida; Edward W Yetter
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1962-11-20
Filing date: 1962-11-20
Publication date: 1966-05-31
Anticipated expiration: 1983-05-31
Also published as: GB1070468A; DE1449058A1

Description

May 31, 1966 E. s. IDA ETAL 3,254,331

I ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION Filed Nov. 20, 1962 7 Sheets-Sheet 1 OCK-IN +s7v. VOLT BUS 57v BUS WGD 22 \JL 0 1 I 23 [9 INPUT SIGNAL l5 CIRCUIT RED 20 I6 GREEN I2 25 4 COMMON FIG-l NON LOCK-IN +57 VOLT BUS I0 NPUT 2o EIIGNAL GREEN cIRcuIT FIGZ f f INVENTORS RD 5. IDA RED EDWA BY EDWARD W. YETTER ATTORNEY y 1966 E. s. IDA ETAL 3,254,331

ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION EDWARD W. YETTER ATTORNEY 7 Sheets-Sheet 3 E. S. IDA ETAL ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION INVENTORS EDWARD S.IDA EDWARD W. YETTER ATTORNEY mo m @E k 1 m2 Emmi. mw mm Tmw m? jilwo I? b m5 M3202 xuwzi n W 5 S w m m D MW H202 wwml m0 no x2325 w j u vm k mam Ema? J mm P S mm 512: Av 6 v F M 5 3 AV 2x54 h. R A Q d W H 1| J aw M3902 9H 2 w an w o\ NP 3 ||||Il||ll|l|| on m V 3 Q 8 8 xuwzE z 5&8 N E on. S L M 4 m2 50 8 A YA 6. 26 5 20 Ema,

May 31, 1966 Filed Nov. 20, 1962 y 1966 E. 8. [DA ETAL 3,254,331 T ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION Filed Nov. 20, 1962 '7 Sheets-Sheet 4 +57 VOLT BUS RNGBACK 98 LAMP 78 +150 VOLT BUS TO SECON D BRABCH CIRCUIT RING BACK AUDlBl BUS I23 FLASHER BUS 1 0 F166 FIGBA 57 VOLT BUS T Lu +|O5 VOLT BUS ACK. BUS

FIG. 8B

FIG-7 INVENTORS EDWARD S. IDA BY EDWARD W. YETTER 1 T- QWE ATTORNEY May 31, 1966 E. s. IDA ETAL ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION '7 Sheets-Sheet 6 Filed Nov. 20, 1962 mOE A E2 25 51 2 A a SEQ? mom m n W n N: 20228 rll Me R mam o2+ INVENTORS EDWARD S. I DA BY EDWARD W- YETTER 7/ gwcm ATTORNEY y 3 1966 E. s. IDA ETAL 3,254,331

ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION Filed Nov. 20, 1962 7 Sheets-Sheet 7 COMMON 5 BUS AUDIBLE BUS FLASHER BUS +57 VOLT BUS INVENTORS EDWARD S. IDA EDWARD W. YETTER ATTORNEY United States Patent 3,254,331 ALARM ANNUNCIATOR WITH INDEPENDENT ACKNOWLEDGEMENT INDICATION Edward S. Ida, Folsom, and Edward W. Yetter, West Chester, Pa., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Filed Nov. 20, 1962, Ser. No. 238,867 6 Claims. (Cl. 340-2132) This invention relates to an alarm annunciator, and particularly to an electrical alarm annunciator which furnishes additional information regarding the state of the point monitored and, further, which is adapted to either pulse type or steady current alarm signal actuation.

Modern manufacturing operations require a more or less continuous monitoring of a multiplicity of operating conditions in rapid sequence, and this has led to a proliferation of independent sensing circuits, each of which is adapted to monitor, or in some instances directly effect, aspecific process step. It is imperative that management have positive assurance at all times as to the moment-bymoment status of each individual operating condition as sensed by the associated monitor circuits, which often total hundreds or even thousands of points, as the individual circuits are customarily called. Thus, there is a strong requirement for simplicity in design in order to reduce the high aggregate cost of the annunciators, coupled with extreme reliability in process surveillance service.

A convenient method of ascertaining whether a control point is, at any given time, in safe or unsafe state is to provide means establishing a unique electrical circuit corresponding to the existing point condition. It is practicable to appraise the status of large numbers of points by rapid, repetitive scanning techniques wherein points are sampled in orderly sequence and a characteristic electrical pulse elicited as the signal of safe or unsafe status, respectively, US. application Ser. No. 108,521, now Patent No. 3,201,572, assigned to the same assignee, teaches a control method and apparatus relying on electrical pulse transmission as the effective control agency, and it is a simple matter to incorporate in such a device additional circuitry routing a tell-tale pulse confirmatory of point status to an annunciator of the design of this invention, which is well-adapted to pulse-type operation,'but is still versatile enough for employment with steady current alarm inputs should this be desired.

An object ofthis invention is to provide an alarm annunciator capable of actuation responsive to electrical pulses as well as to steady current signals. Another object of this invention is to provide an alarm annunciator capable of furnishing more complete information on monitored point status, such as, for example, instant advice of restoration of a point to normality. Another object of this invention-is the provision ofan alarm annunciator particularly adapted to the convenient inclusion of auxiliaries providing additional information with respect to the occurrence of anomalies in the condition monitored, or the indication of steps taken corrective of -any anomalies signaled. Other objects of this invention Patented May 31, 1966 embodiment of basic non lock-in type annunciator according to this invention,

FIGS. 3A-3C are schematic representations of the lefthand branches only of the embodiments of FIGS. 1 and 2, I

detailing three preferred designs of input circuit each employing a different type of alarm signal actuation, FIG. 3A being directed to pulse utilization, FIG. 3B to normally closed contact, steady current utilization and FIG. 3C to normally open contact, steady current utilization,

FIG. 4 is a schematic representation of another embodiment of this invention utilizing a diode as the electronic blocking means in the left-hand circuit branch instead of the transistors employed in the embodiments of FIGS. 1 and 2, this figure showing two complete independent annunciators of which the left-hand one is a lock-in design whereas the right-hand one is a non lock-in design.

FIG. 5 is a schematic representation of a preferred circuit arrangement of audible alarms, acknowledgement pushbuttons, and lamp flasher auxiliaries for the annunciaare to provide an electrical alarm annunciator which is tor of this invention, inter-connection with the annunciator proper being, illustrated with respect to the lock-in embodiment of annunciator shown in FIG. 4,

FIG. 6 is a schematic representation of a preferred embodiment of Ring Back auxiliary adapted for use with the lock-in species only of this invention, inter-connection with the annunciator proper being illustrated with re- .spect to the lock-in embodiment of annunciator shown either the lock-in or non lock-in species of this invention,

interconnection withthe annunciator proper being illustrated with respect to the left-hand branch of the embodiments of annunciator shown in FIG. 4,

' FIG. 7A is a schematic representation of two individual annunciator embodiments, one of the lock-in type and the other a non lock-in, complete with First On, Ringback, flasher and audible alarm auxiliaries,

FIGS. 8A and 8B are schematic representations of embodiments of alarm indication and acknowledgement verification branch circuits, respectively, of a lock-in type annunciator wherein neon lamps are substituted in a dual capacity for the switching element and alarm lamp collectively of the embodiments of FIGS. 1 and 4, with the points of pulse signal introduction rearranged to suit the changed polarity requirements,

FIG. 9 is a schematic representation of two preferred designs of lock-in type annunciatorcircui't utilizing neon lamps as the visual indicators and also as switching elements, the left-hand embodiment being pulse-actuated, whereas the right hand embodiment is steady direct current actuated with a switch in normally closed contact state for the signal input,

FIG. 10 is a schematic representation of yet another embodiment of lock-in type pulse-actuated annunciator utilizing neon lamps and a transistor in the first branch.

circuit thereof, and

ment of alarm indication branch circuit utilizing a switch in normally open contact state for the signal input.

Generally, the electrical annunciator of this invention comprises, in combination, a D.-C. supply, a first bnanch circuit and a second branch circuit connected in parallel circuit relationship one to the other across the DC.

supply, the first branch circuit being'provided with an alarm indication lamp together with alarm indication lamp control means responsive, first, to receipt of a signal signifying the existence of an abnormal state in a point monitored establishing a distinctive illuminated stateof .the alarm indication lamp and, second, to receipt or a signal signifying the restoration of the point monitored by the employment of two more or less self-contained circuits, the purpose of the first of which is to handle alarm indications incident to deviation of the point monitored from normal behavior, whereas the purpose of the second .is to provide an acknowledgement verification facility. Such an approach has very great advantages over that hitherto followed in annunciator design, because there exist three items of information which must be communicated, namely: (a) normal condition, (b) alarm (or abnormal) condition and (c) acknowledged condition. If only one lamp is employed for the entire communication, three states of illumination are required as an absolute minimum, whereas, when two'independent lamps are used, only two states of illumination are necessary. The essential electrical circuitry, especially where solid state components are employed, is much simpler and more reliable in the latter case.

Perhaps an even more important advantage of the twolamp system is the fact that, in rapid scanning, mu-ltiplexed monitoring systems, there exists the ability to accept repetitive information during each successive soan cycle without disturbance to the sequence of operation of any given annunciator. Thus, the scanning alarm monitor is not required to remember that it previously gave an OFF or an ON signal to the annunci ator, so as to require suppression of later-repeated signals.

Referring to 'FIG. 1, there is shown a preferred embodiment of basic lockain type alarm annunciator according to this invention wherein the input signal circuit is represented simply as a block 10 by way of expressing the generality of choice possible in signal input, all as hereinafter described with particular reference to FIGS. 3A to 3C, inclusive.

T-he tannunciator unit, one of which is reserved exclusively to each point monitored, comprises a D.-C. supply represented by leads, 1 1 and :12, of which 11 can typically be la +57 v. lead whereas 12 is a grounded conductor common. Two parallel-connected branch circuits are provided across leads 1 1 and 12, of which the left-hand one shown in FIG. 1 is referred to in this description and the claims 'as the first branch circuit, which is reserved to alarm indication exclusively, whereas the right-hand one is denoted the second branch circuit, which is reserved to acknowledgement verification exclusively.

The first branch circuit has connected therein, in series electrical arrangement, a current-stable, negative resistance switching element which can typically be, as indicated, a 4-l ayer diode 14 (e.g., a Type 4E 40-28, or a IN 3304), a P N-P transistor 15 (typically a Motorola Type 2N398A) as the electronic blocking means and a red alarm indication lamp 516 (typically, a GB. No. 1835, 55 v., 50 ma. miniature lamp). put signal to the annunciator is introduced from input signal circuit '10 via conductor 18 connected to the base of transistor 15.

The second branch circuit includes a 4-1ayer diode 19 (Type 4 E 8028) similar to diode 114, and a green acknowledgement verification lamp 20, similar to lamp 16. The second branch circuit also incorporates a diode 21 (typically a type SR169Z) and is capacitor-coupled to the first branch circuit via capacitor 22 (typically 0.01

The negative polarity inmfd. size) and conductor 23, connected on the one hand between diode '14 and transistor #15, and on the other between diode 2'1 and diode 19. Finally, there is provided a normally closed, manually-operated switch 25 in circuit between the second branch circuit and D.-C. supply leads 1 1 and 12.

The circuit for the preferred embodiment of the basic non lock-in .annunciator according to this invention, shown in FIG. 2, is identical in most respects to that described 'for the lock-in embodiment of FIG. 1. Accordingly, all counterpart elements are therefore denoted by the same reference numerals, but with -a prime appended. The coupling between first and second branch circuits is, in this design, achieved by a capacitor 26 (typically a 0.25 mfd. size) and a conductor 27, connecting, in this embodiment, between transistor and red alarm indication lamp 16 on the one hand, and green acknowledgement verification lamp 20 and diode 19 on the other. It will be noted that the relative location of the acknowledgement verification lamp 20 is changed from that of lamp 20, in that lamp 20 is, in this case,

interposed between

diodes

21 and 19, instead of to one side of them.

Before proceeding with a description of the operation of the apparatuses of FIGS. 1 and 2, it is believed desirable to describe the three principal types of signal input which can be conveniently employed with the annunciator. Thus, FIG. 3A shows a preferred design of signal input circuit intended for use with positive and negative electric pulses, such as those hereinbefore referred to with respect to US. application Ser. No. 108,521. Here it is necessary to utilize a positive polarity transistor biasing bus 30 (typically +37 v., i.e., less than the +57 v. of supply lead 11) connected through resistors 31 and 32 (each typically 3.9K ohms) between which latter the negative polarity 0N pulse signal signifying the existence of an abnormal state in the point monitored, is introduced via lead 33, whereas the positive polarity OFF pulse signal, signifying the restoration of the point monitored to normal state, is introduced via lead 34. Each of these pulses is typically supplied at a voltage level of about :20 v. referred to the +37 v. bus 30.

Another common input is that depicted in FIG. 3B, employing a steady D.-C. signal drawn from D.-C. supply lead 11 through a normally closed switch 36' connected to the grounded common 12 via a resistor 37 (typically 7.5K ohms). In this construction switch 36 is maintained closed via the mechanical connection indicated schematically in broken line representation at 33 at all times during which the point monitored is in normal behavior, being open at all other times. As in FIG. 3A a positive polarity biasing signal is imposed on the base element of transistor 15 via two series-connected resistors 31 and 32 (each typically of 3.9K ohms value), :1 capacitor 40 (typically 1 to 10 f. size) being connected midway between resistors 31' and 32 and positive lead 11 in order to attenuate extraneous interference signals, whereas a diode 41 (typically a type 1N90) is connected in shunt around these resistors between switch 36 and the base element of transistor 15. The function of diode 41 is that of a protective element shunting leakage current from transistor 15, which sometimes exists in the case of a Ge transistor but is usually not a problem where an Si transistor is employed. Such a leakage current interferes with forceful turn-off of transistors at the input shunting resistors; however, the difficulty can also be cured by utilizing a 3 v. turn-off reverse bias as an alternative if desired.

Yet another signal input which is frequently encountered is that illustrated by FIG. 3C, utilizing a steady D.-C. signal current drawn from lead 11 via a branch conductor 43 incorporating resistor 44 (typically 7.5K ohms) and switch 45, which is retained normally open by mechanical connection 46, shown in broken line representation, at all times when the point monitored is in normal behavior, and, conversely, is brought to closed circuit when the point monitored goes abnormal. Again, a positive polarity transistor biasing signal is applied via

resistors

31 and 32" (each typically 3.9K ohms) and resistor 44 connected in series one with the other between branch conductor 43 and the base element of transistor 15, capacitor 40' bridging lead 11 and the resistor midpoint being identical in value and purpose with capacitor 40 of FIG. 3B.

The operation of the basic lock-in annunciator of FIG. 1 is the same regardless of the nature of the input signal circuit. Thus, imposition of a negative polarity signal, either in the form of a relatively transient pulse or a prolonged D.-C. steady current via a specific input circuit such as one of those described, into the base element of transistor 15, signifying the existence of abnormality at the point monitored, biases 4-layer diode 14 and transistor 15 to conductive state. This establishes relatively heavy current passage through the first branch circuit, with consequent illumination of red lamp 16 from full darkness to full brightness. The passage of current exceeds the minimum holding current of 4-layer diode 14, which thereafter maintains lamp illuminating current flow through the first branch circuit.

Simultaneously, referring to FIG. 1, a transfer of voltage from capacitor 22 back-biases diode 21 and forward biases 4-layer diode 19, thereupon exceeding its threshold voltage value, thereby initiating heavy current conduction therethrough, so that lamp illuminating current continues to be supplied through green acknowledgement verification lamp 2%] for so long as manually operated switch 25 remains closed.

When the point monitored is restored to normality, either by corrective action taken by personnel in response to the warning given by the annunciator or in the absence of any human intervention whatever, a corresponding signal is delivered by input circuit 16, which biases transistor 15 to its non-conductive state. This halts all current flow through the first branch circuit and, of course, red lamp 16 immediately reverts to its nonilluminated state; however, this has no effect on the second branch circuit, since capacitor 22 is effective in the lock-in embodiment of this invention solely to turn on the current in the second branch circuit but not to turn it off. Accordingly, illumination of green lamp persists until manual switch 25 .is opened by an attendant, who is instructed to take this action only after taking cognizance of the fact that an abnormality has occurred at the point monitored.

It frequently happens that the abnormality at the point monitored consists of one or more brief duration incidents Which operate successively to' switch the first branch circuit on and off in sequence. Since the second branch circuit responds to each switching on of the first branch circuit, the green acknowledgement verification lamp 20 retains the information that an anomaly has occurred until cleared by opening of switch 25, or switches back on subsequent to any given acknowledgement if the alarm condition repeats, thereby preserving information by a lock-in type action completely independent of the first branch circuit.

The operation of the basic non lock-in annunciator embodiment of FIG. 2 is in all respects the same as that of the lock-in embodiment, except that capacitor 25 is, in this instance, located past transistor 15 of the first circuit branch and is, in addition, of much larger size than capacitor 22, so that it is operative also to extin uish current flow through the second branch circuit (by effectively momentarily reducing the current flow to switching diode L9). The larger size of capacitor 26 as compared with capacitor 22 is to afford the somewhat larger R-C time constant required to effect turn-off of the solid state diode i19, turn-on being inherently significantly faster, as conducted with the embodiment of FIG. 1. Thus, acknowledgement verification lamp 20 reverts to its nonilluminated condition simultaneously with switch off of red alarm indication lamp 16. Nevertheless, this embodiment still provides an acknowledgement facility operable at all times in the same manner as for the embodiment of FIG. 1 prior to return to normality of the point being monitored.

The signal provided by the second branch circuit is, especially with the lock-in design, exceedingly important, in that it, in effect, constitutes the memory that an abnormal condition has, in fact, existed at the point monitored, even though that abnormality may have been of only very brief duration, and thus have escaped notice so far as the transient illumination of the red lamp of the first branch circuit was concerned. It is, therefore, desirable to provide a second green lamp in shun-t with the first as a reserve standf'oy should the first green lamp \burn out or otherwise fail. In addition, audible alarm and flashing illumination of the green acknowledgement verification l-amp are very desirable auxiliary features in order to better gain the notice of an attendant, and all of these features are shown in FIGS. 4 and 5 taken together. Although the embodiments of annunciator per se portrayed in FIG. 4 are dififerent from those of FIGS. 1 and 2 in yet another respect, namely, the substitution of a diode for the transistor as the electronic blocking means in the first branch circuit, it will be particularly understood that this has no bearing whatever on the choice of alarm presentation auxiliaries. Such auxiliaries are completely applicable to all other embodiments of the invention, including those of FIGS. 1 and 2, it being understood that it is then convenient to relocate manual switch 25 (or 25') so that it will simultaneously discontinue any additional alarms co-oper-ating with the acknowledgement verification lamp of the second branch circuit.

Referring to FIG. 4, there are shown two independent annunc-iator units connected across common D.-C. supply leads 11 and 12, the left-hand unit of which is of the lock-in type, whereas the right-hand unit is of the non lock-in type, this choice of representation having been made to conserve drawing requirements.

When diodes are used instead of transistors in the first branch circuit, signal input is restricted to the pulse type hereinbefore elaborated generally with respect to FIG. 3A, with the difference that the abnormality warning ON signal and the abnormality discontinuance OF'F signal must now be applied at different locations in the first branch circuit. Any disadvantage resident in this fact is cured by the latitude afforded the designer in choice of signal polarity and voltage magnitude as well as freedom or" place of signal imposition, which will be understood by persons skilled in the art. For purposes of representation solely, negative polarity ON signals and positive polarity OFF signals are hereinafter described as the circuit actuation agencies.

Referring to FIG. 4, all branch circuits are shown as provided with the identical current-stable, negative resistance switching elements, conveniently in the form of 4-layer diodes (all typically 415 -28 types) 14", 19, 14, and 19', corresponding to 14, 19 and 14, 19', and also with diodes 21" and 21", identical with 21 and 21, respectively, and indication lamps 15", 20" and 16", 20' identical with

lamps

16, 20 and '16, 20', respectively, of FIGS. 1 and 2. However, diodes 49 and 49 (typically type SR1692) are substituted for the transistors 15 and 15', respectively, of the embodiments of FIGS. 1 and 2, requiring imposition of the current-limited negative polarity ON pulse (typically -80 v. 28 ma.) via conductor 50 (or 5'0) connected into the first branch circuit between switching element 14" (or 14") and diode 49 (or 4 9). Similarly, the positive polarity OFF pulse of magnitude imposing effectively zero volts across the switching element is necessarily introduced via conductor 51 (or V 51 connected into the first branch circuit between diode 49 (or 49') and the red alarm indication lamp 16" (or 16"). In the case of the non lock-in embodiment of FIG. 4, the OFF signal pulse is applied simultaneously to both branch circuits via a bridging conductor 52 provided with diodes 53 and 53' (typically type SRl692) in the individual halves reserved to the first branch circuit and the second branch circuit, respectively, which are coupled one to the other in both embodiments by an upper bridging conductor 54 (or 54') provided with capacitor 55 (or 55) typically of 0.01 mfd. size.

As previously mentioned, a reserve green acknowledgement verification lamp 20a (or 20a) is provided in shunt connection with lamp 20" (or 20") in the second branch circuit, and audible and flashing signal auxiliaries are added by way of improving the alarm presentations.

Thus, referring to FIGS. 4 and collectively, an audible bus 58 is preferably provided for servicing a plurality of annunciator units, the connection of only one, e.g., a lock-in embodiment incorporating a standby reserve green lamp, such as the left-hand unit of FIG. 4, being portrayed in FIG. 5 by detailing solely the connections to the green lamps and 20a". The second branch connections to bus 58 are made in all cases through a resistor 59 (or 59), typically 330 ohms, which effectively interposes enough resistance in series with lamps 20" and 20a" to bring them to approximately half brilliance during alternate half cycles of operation of the flasher hereinafter described.

The remaining circuit completion connection for the second branch circuit is via diode 60 (or 60), typically a type SR1692, and conductor 61 (or 61') running to flasher bus 64. Since, in most cases, it is desired to effect acknowledgement of a plurality of points monitored simultaneously, audible bus 58 is provided with a common pushbutton switch 65, and flasher bus 64 is similarly provided with a common pushbutton switch 66 ganged for simultaneous operation with switch by the mechanical connection indicated schematically in broken line representation at 67. These switches together correspond functionally with

manual switches

25 and 25 of FIGS. 1 and 2. All pushbutton switches are shunted by individual resistors 68 (typically 100K ohms each) which restore the voltage across any current-stable, negative resistance switching elements, such as the 4-layer diode 19, and its counterparts, after disruption of the heavy current supply path produced by opening of the switches 65,. 66 and their counterparts. This is a precaution against possible spurious switching action on the part of these diodes which can sometimes result from a rapid voltage rise thereacross in the absence of current-limiting such as provided by these resistors.

The audible alarm, indicated generally by block 70 is a conventional relay or voltage controlled oscillator, which is provided with a voltage-limiting diode 71 connecting audible bus 58 with the common bus 12. Diode 71 is shunted by resistor 72 (typically 100 ohms), so that returning current flow developing a signal in excess of about /2 v. actuates the audible alarm. It might be mentioned that diode 71 limits the voltage drop to about one volt, no matter how many green lamps 20", 20a", or their counterparts are on, whereas resistor 72 averts actuation of audible alarm 70 by any minor leakage currents which could otherwise cause the audible alarm to sound.

Flasher 73 connected between flasher bus 64 and common bus 12 is a conventional motor-driven cam-operated switch, or its solid-state equivalent, which, when its contact 73a is closed, shunts current around resistor 59 via diode 60 through the flasher, which operation repetitively dims

lamps

20 and 20a" during each half cycle of operation of flasher 73. It will be understood that flasher 73 coincidentally also modulates the current supplied to audible alarm 70, so that the audible alarm goes on and off at the flashing rate (typically, one cycle/sec), which is desirable. Finally, the diodes corresponding to diode 60 constituting components of neighboring annunciator units isolate each of these annunciators from concurrent operation with those monitoring'points in alarm.

FIG. 5 shows additional circuitry provided for yet other optional auxiliaries, such as First-On indication and Ring Back; however, description of these features is postponed until the related circuits of FIGS. 6 and 7 are hereinafter taken up.

Turning now to the operation of the specific embodiment of FIG. 4, the introduction of a negative polarity ON pulse via lead 50, signifying the existence of an abnormal state in the point monitored by the annunciator, immediately increases the effective voltage drop across switching diode 14 and, the limiting threshold of diode 14" being exceeded, initiates heavy current flow through the first branch circuit, thereby illuminating the red alarm indication lamp 16". The ON pulse simultaneously develops a charge within capacitor 55 via conductor 54 which immediately transfers a voltage thereacross, effectively increasing the voltage drop across switching diode 19", exceeding the voltage threshold thereof and initiating heavy current flow through the second branch circuit. This illuminates

green lamps

20 and 20a, the acknowledgement verification lamps, by completion of the circuit to common bus 12 via both audible'bus 58 and flasher bus 64, as best shown in FIG. 5. Since the latter'circuit path is cyclically interrupted by opening of motor-driven switch 73a within flasher 73, there is simultaneously obtained both flashing illumination of green lamps 20" and 20a" and a fluctuating audible alarm signal emitted by audible alarm 70, calling the attendants attention to the fact that an abnormality has come into existence at the particular point serviced by the annunciator. In usual practice the attendant will immediately acknowledge that he has become aware of the existence of the abnormality by momentary opening of the normally closed ganged

pushbutton switches

65 and 66, thereby discontinuing both the audible alarm and the flashing illumination of lamps 20" and 20a", whichrevert to their non-illuminated state. However, if the abnormality persists past the time of acknowledgement, red alarm indication lamp 16" remains illuminated. It is only when further action is taken by the attendant in correction of conditions causing the abnormality that a positive polarity OFF pulse is transmitted to the first branch circuit via conductor 51. This positive pulse, by back-biasing diode 49, effectively reduces the. current flow through switching diode 14" to below the minimum holding current of this diode, thereby switching the diode off and discontinuing current flow in the first branch circuit, so that red alarm indication lamp 16" (FIG. 4) goes olf.

Turning now to FIG. 6, it is frequently desirable to incorporate a Ring Back auxiliary with lock-in type annunciators, and this is readily accomplished with the invention design. Ring Back is obtained by providing an independent branch circuit connected in parallel relationship to the first and second branch circuits of the basic annunciator per se across D.-C. supply leads 11 and 12, connection with the latter lead being conveniently made via the common flasher bus 64 shown in FIG. 5 and a separate common Ring Back audible bus 75.

The individual components'connected in series circuit in the independent Ring Back branch circuit correspond generally to those hereinbefore described for the basic annunciator circuit and consist of a current-stable, negative resistance switching element, such as the 4-layer switching diode '77 (typically a type 4E80-28), a Ring Back indication lamp 78 (typically a type No. 1835 identical with lamps 16, 2t) and their counterparts hereinbefore described), which can be of distinctive amber color, and two parallel-connected diodes, 79 and 8t) (typically each of type SR1692), completing the circuits to

buses

64 and 75, respectively. Again, to obtain cyclic-a1 dim-to bright operation of Ring Back lamp 78, a resistor 81 (typically of 680 ohm value) is interposed between diode 8t) and Ring Back audible bus 75. Since a completely independent Ring Back audible signal of distinctive pitch is desirable to distinguish audibly between the eration.

of the Ring Back audible alarm is provided by normally closed Ring Back acknowledgement pushbutton switch S7 interposed in bus 75 ahead of audible alarm 84. Switch 87 is ganged for simultaneous operation through mechanical connection 88 with a companion normally closed pushbutton switch 89, corresponding to switch 66, interposed in flasher bus 64 and, again, shunt resistors 68 are connected across these switches to avert any spurious operation of switching diode 77.

, Co-ordination of the independent Ring Back circuit with the basic annunciator circuit is obtained by coupling with the annunciator first branch circuit, the red alarm indication lamp 16' of which is shown in broken line representation in FIG. 6, via conductor 91 having interposed therein capacitor 92 (typically 0.01 mfd. size), and with the second branch circuit by conductor 93 connected just ahead of green

acknowledgement verification lamps

20 and 20a, also shown in broken line representation. Conductor 93 has interposed therein Zener diode 96 (typically a 56 v. type IN732), and, preferably, a currentlimiting R-C network consisting of parallel-connected resistor 97 (typically K ohms, /2 watt) and capacitor 98 (typically 0.1 rnfd. size). The purpose of resistor 97 is to limit D.-C. current flow while the purpose of capacitor I 98 is to pass A.-C. current flow through Zener diode 96,

Acknowledgement of Ring Back is accomplished simply by the attendants momentary opening of the normally closed Ring Back acknowledgement pushbutton 87 (FIGS. 5 and 7A) together with its gang-associated switch 89 in flasher bus 64.

Yet another optional auxiliary which is frequently advantageous applicableto both lock-in and non lock-in annunciators, is that of First-On indication, a preferred embodiment of sub-circuit for which is shown in FIG. 7. This entails provision of an independent branch circuit reversed to First-On indication at each point monitored, which branch circuit is connected in generally parallel relationship with respect to the annunciator proper first that Ring Back lamp 78 come into illumination when red alarm indication lamp 16 turns off, providing, however, that the attendant has already acknowledged the existence of an anomaly in the monitored point by having previously opened the pushbutton acknowledgement switch 65. The reason for this is that it is ordinarily not desirable to obtain Ring Back action for points only momentarily in alarm. Accordingly, concerted action is called for by both the first branch circuit and the second branch circuit of the annunciator applicable to the independent Ring Back circuit.

The operation of the Ring Back auxiliary involves the transfer of a voltage across capacitor 92 incident to the extinction of red alarm indication lamp 16 which creates a voltage drop across switching diode 77 exceeding its threshold level, thereby initiating heavy current flow through diode 77 into the Ring Back branch circuit. However, if the annunciator second branch circuit is in its ON state, as evidenced by continued illumination of green

acknowledgement verification lamps

20 and 20a prior to abnormality acknowledgement by the attendant through operation of switches 65-66, Ring Back switching diode 77 will be shunted by the existence of a voltage dropping path through lamp 78, Zener diode 96, conductor 93 and the annunciator second branch circuit. Under these circumstances switching diode 77 will be inhibited from switching ON and Ring Back lamp 78 will remain unilluminated.

The foregoing operation is clarified further by reference I to FIG. 7A, 4-layer diode 19 upon heavy current flow therethrough making line 93 swing to a high positive voltage reversing the bias on Zener diode 96, to drive it into high negative conduction. The high negative current thus impressed through 4-layer diode 77 prevents its op- Thereafter, upon ringback, Zener diode 96 is forwardly biased so as to pass little current, and capacitor 92 transfers a negative pulse to trigger on 4-layer diode 77.

and second branch circuits, as well as' with any other auxiliaries, such as the Ring Back hereinbefore described, across D.-C. supply lead 11 on the one hand and a First-On acknowledgement bus 101 connected in turn to the common bus .12- Referring especially to FIG. 7, the independent First-On branch circuit incorporates in series connection individual components identical with those of the annunciator first and second branch circuits, including diode 102 (typically a type SR1692), a First-On indication lamp 103 of any desired color (e.g., white), preferably of the same type as

lamps

16, 20, 20a and their counterparts hereinbefore described, and a current-stable, negative resistance switching element, such as 4-layer switching diode 104 (typically a type 4E80-28 identical with the switching

diodes

14,19 in-the annunciator proper). The First-On branch circuit is coupled to the annunciator first branch circuit, indicated fragmentarily in broken line representation, via conductor 105 provided with capacitor 106 (typically 0.01 mfd. size).

Since all First-On auxiliaries are connected in a v common circuit arrangement which would illuminate the lamps in all of them simultaneously, and thus lose the First-On indication which is the sole function of the auxiliary, each must be provided with means positively preventing such a contingency. This necessitates the use of individual shunting circuits around each of the switching diodes 104 which are of the same design as those hereinbefore described for the Ring Back auxiliary of FIG. 6. Thus, there is provided a Zener diode 108 preferably in series circuit with a current-limiting R-C network, incorporating resistor 109 (typically, 5K ohm size) parallel-connected with capacitor 110 (typically, 0.1 mid. size), connected to the First-On branch circuit between lamp 103 and switching diode 104. The other terminal of the shunting circuit is connected to a common First- On clamp bus 111, to which all other First-On circuits are similarly connected. Clamp bus 111 can either be floating, as shown in FIG. 7, in the sense that no connection whatever with common bus 12 is required, or it can be connected to the latter through a rather large value resistor (typically K ohms).

By way of explaining the operation, it is assumed that the monitored point serviced by the First-On unit shown in FIG. 7 goes abnormal. The alarm condition is immediately signaled by the annunciator first branch as hereinbefore described, which imposes a charge of polarity and magnitude on capacitor 106 via lead exceeding the threshold level of switching diode 104, thereupon causing heavy current flow through the First-On cir-- cuit, together with illumination of the First-On indication lamp 103. The attendant acknowledges receipt of the information by momentarily opening normally closed acknowledgement switch 100 (FIG. 5) interposed in the First-On acknowledgement bus 101, which restores the alarm received from its monitored .point, it is, of course, necessary that the particular First-On circuit of 'FIG. 7.

remain inactive. This operation is assured by Zener diode 108, which prevents clamp bus 111 from ever becoming more than a few volts positive with respect to common bus 12, when a neighboring First-On unit, all of which are connected to the same clamp bus 111, is turned on. Accordingly, the shunting action of Zener diode 108 with respect to switching diode 104 is effective to prevent the latter from ever reaching the 80 v. threshold which is necessary to produce switching action, and no two First-On units can thus ever be actuated simultaneously, provided, of course, that there exists a few millisecs. delay between any two alarm incidents.

As most clearly seen in FIG. 7A, capacitor 106 switches on 4-layer diode 104, Zener diode 108 being highly reverse biased so as to pass a high negative current to clamping bus 111. This high negative current is drawn through 4-layer diode 104 and Zener diode 108 of the right-hand module, as well as the counterpart diodes in all other modules connected in the same system, thereby reverse biasing all other 4-layer diodes corresponding to 104, preventing their subsequent conduction.

Turning now to FIGS. 8A and 813, it is entirely practicable to substitute a neon lamp (typically type LNE48) in the dual capacity of a replacement for both the indication lamp and the switching element of either the first or second branch circuits (or both of them) in any of the annunciator embodiments hereinbefore described.

A preferred pulse-actuated design of first branch circuit is that shown in FIG. 8A wherein the B+ supply lead is denoted 11a, carried at a higher voltage level (typically 105 v.) than its previously described counterpart 11 to accommodate the characteristics of the neon lamp 115. As will become clear from the following description, lead 122, maintained at typically +150 v., is necessary to the signal input, so that it is convenient to derive the +105 v. supply of the D.-C. supply lead pair from lead 122 by connection with it through resistor 116. Voltage dropping resistors 116 (typically 10K ohms value) and 117 (typically 6.8K ohms value) are respectively provided ahead of, and after, lamp 115, thereby establishing convenient base levels for imposition of the ON pulse (typically v.), which is the signal signifying the existence of an abnormal state in the point monitored, via lead 119, and the OFF pulse (typically +50 v.), which is the signal signifying restoration of the point monitored to normal value, via lead 120. In this annunciator design the connection with the associated second branch circuit is via conductor 121, provided with the usual coupling capacitor (not shown), represented in broken line representation in FIG. 8A.

Since lead 11a is the common B+ bus for a plurality of annunciator units, it is necessary to isolate each individual first branch circuit by a diode 118 (typically a type SR1692), and to also provide a clamping Zener diode 124, only .one of which latter is required for a plural annunciator set up, connected from the back side of any specific diode 118 to common bus 12a. With this provision, lead 110 is effectively biased at +105 v., which is a very satisfactory B+ level for this embodiment.

In operation, the negative polarity ON pulse imposes a voltage across neon lamp 115 SUfl'lClfiDt to fire it, which is a substitute for the switching role previously performed by switching diode 14 and its counterparts, at the same time illuminating the lamp, so that an indication of abnormality existence is given equivalent to that of red lamp 16, FIG. 1, or its counterparts previously described. Also, when the abnormality is rectified, or disappears, the OFF pulse imposed via lead 120 effectively lowers the voltage drop across lamp 115, which thereupon goes out, discontinuing its alarm indication. In this connection it should be noted that neon lamps of the type described sustain conduction, once fired, at a potential level of to v., so that the lead 11a at v. potential is entirely ample to keep lamp in illumination, once it is turned on. Turn off of lamp 115 requires the development of a voltage drop in the lamp anode circuit, so that lead 122 at +150 v. merely serves as the necessary current supply lead, via load resistor 116, required on the part of the signal input to efiect this operation.

It will be understood that a first branch circuit utilizing a neon lamp as described for the embodiment of FIG. 8A can be readily combined to form a complete annunciator unit according to this invention with a second branch circuit of any of the designs hereinbefore described or, alternatively, the second branch circuit can utilize a neon lamp in the same general manner as that taught for FIG. 8A.

Thus, referring to FIG. 8B, the second-branch circuit can consist simply of an acknowledgement verification lamp 127 (again typically a type LNE4S) connected, on the one side, to the 13+ lead 111! through a diode 128 (typically type SR1692) and on the other side through a current-limiting resistor 129 (typically 6.8K ohms) to a common acknowledgement bus 130 provided with an acknowledgement switch such as pushbutton switch 100, FIG. 5 (which, in this case, should not be provided with a shunting resistor 53), in turn connected to a common bus 12, which latter two components are not shown in FIG. 83. Finally, the second branch circuit is coordinated with the first branch circuit by a conductor 131. having interposed therein a capacitor 132 (typically 0.01 mid. size), thereby completing the assembly of a basic lock-in type annunciator unit.

Operation is in all respects similar to that of the embodiments hereinbefore described, acknowledgement verification lamp 127 serving in the same dual capacity as already explained for lamp 115 of the first branch circuit, so that lamp 127 fires practically simultaneously with lamp 115 upon transfer of a voltage from capacitor 132 responsive to receipt by the first branch circuit of an ON signal pulse input via lead 119 signifying existence of an alarm condition at the point monitored.

Lamp 127 thereafter continues in illumination until the attendant signifies receipt of the information by momentary opening of the acknowledgement switch (not shown) interposed in circuit with acknowledgement bus 130. The annunciator circuit is thereupon restored to its original state, ready for handling of any new alarm incidents whenever they should occur.

The detailed circuitry for two basic lock-in type annunciators employing neon lamps in the dual capacity described, and provided with audible bus and flasher bus auxiliaries as hereinbefore described for other embodiments, is shown in FIG. 9, the left-hand annunciator being pulse-actuated whereas the right-hand annunciator is steady current-actuated.

Components in the pulse-actuated embodiment of FIG. 9 are represented by the same reference numerals as employed for their counterparts of FIGS. 8A and 813, except with a prime appended, and the identity is believed amply clear, although certain slight alterations were made to accommodate the auxiliaries and the differing signal inputs. Thus, the resistor corresponding to resistor 129, FIG. 8B, is now effectively split into two parts (each, typically, of 6.8K ohm value), the first, 129a, being connected between acknowledgement verification lamp 127' and conductor 133 having in series with it diode 134, which establishes circuit with flasher bus 130", whereas the second, resistor 12%, is interposed after resistor 129a in the circuit path running to the audible bus 130. The operation of this embodiment of annunciator is exactly as hereinbefore described with respect to FIGS. 8A and 8B, and hence is not repeated.

The right-hand annunciator unit employs normally closed contact actuation in the signal input, being in this respect similar to the signal input portrayed in FIG. 313, so that the existence of an alarm condition in the point monitored is signaled by the opening of switch 141 under mechanical actuation denoted schematically in broken line representation at 142. The first branch circuit, connected across D.-C. supply leads 122 and 12a, consists 13 of neon alarm indication lamp 145 (typically a type LNE48) in series with resistor 146 (typically 6.8K ohm value). This connection to the higher voltage (i.e., +150 v. bus 122') is necessary in order to obtain firing of the alarm indication lamp 145, because, while +105 v. derived from supply lead 11a is eflfective as a neon lamp illumination-sustaining voltage, it is below firing level.

Switch 141 is connected from a point between resistor'144 to audible bus 130' and flasher bus 130".

In operation, switch 141 remains closed in the absence of an abnormal condition at the point monitored, effectively shunting alarm indication lamp 145, which therefore remains unilluminated. When an abnormality arises, switch 141 is opened by mechanical actuator 142, thereupon imposing full voltage across lamp 145, firing it and applying, through coupling capacitor 132", a back bias on diode 128" sufiicient to fire the acknowledgement verification lamp 127", which latter then conducts current to both the associated audible and

flasher alarm buses

130 and 130 as hereinbefore described for the embodiments of FIGS, 4 and 5.

When switch 141 recloses upon restoration of the point monitored to normality, lamp 145 is shunted out and therefore goes dark, whereas lamp 127" remains illuminated until the attendant opens an acknowledgement switch (notshown) identical in all respects with those described for FIGS. 4 and 5. The operation cycle then stands completed until a new anomaly arises at the point monitored.

It will be understood that the annunciator embodiments utilizing neon lampsas both visual indicators and switching elements can, if desired, also be provided with any of the other auxiliaries as well, including Ring Back and First-On.

Yet another lock-in type annunciator employing dual capacity neon lamps as visual indicators, together with pulse signal input, is that shown in FIG. 10. Since the second branch circuit of this embodiment is identical in all respects with the second branch circuit of the righthand embodiment of annunciator shown in FIG. 9, the various components thereof are denoted by the same reference numerals.

In this design the first branch circuit is connected across the +105 v. bus 11a and bus 12a as the D.-C. supply leads, and incorporates the alarm indication neon lamp 151 (typically a type.LNE48), P-N-P transistor 152 (typically type 2N598A) and resistor 3 (typically 6.8K ohms value). The base element of transistor 152 is connected to bus 12a through series-connected resistors 155 and 156 (each typically 3.9K ohms), and the signal input is applied intermediate these resistors in the form of a negative polarity ON pulse (typically 50 v.) supplied through lead 159 and a positive polarity OFF pulse (typically +50 v.) supplied through lead 160.

In operation, the existence of abnormality in the point monitored is signaled by the delivery of the negative polarity ON pulse via lead 159 to the base element of transistor 152, and the transistor thereupon develops a large enough voltage drop to fire alarm indication lamp 151,1.hus illuminating it. Simultaneously, a back bias is imposed through coupling capacitor 132" on diode 128", second branch circuit, to develop firing voltage across acknowledgement verification lamp 127", which imme- A ca-- A positive polarity OFF pulse of magnitude approximately +50 v., delivered via lead 160 responsive to restoration of the monitored point to normality, at once reduces the voltage applied across lamp 151, and the lamp goes dark, completing the operation cycle and plac-, ing the annunciator unit once again in serveillance service.

Still another embodiment of first branch circuit, which is exceedingly simple in design, is that shown in FIG. 11. This design requires use of a normally open contact type signal input, which is not generally regarded with favor by persons skilled in the art, because an accidental break in the circuit, or oxidation at the. contacts barring current passage therethrough, are, of course, both indistinguishable from a lamp indication corresponding to a safe state for the point monitored.

In any case, such a first branch circuit consists simply of an alarm indication lamp 16b connected through a normally open switch across D.-C. supply leads 11b and 12b. Alarm condition for the point monitored is signaled by closure of switch 135 through the agency of mechanical connection 136, which closure must, of course,

' the usual manner via conductor 137 having interposed in series therewith a capacitor 138 (typically 0.01 mid. size). The operation of this embodiment is in all respects similar to that of the others already described and is, therefore, not detailed herein.

While this invention has been illustrated by circuits employing P-N-P type transistors, the use of the N-P-N type is equally practicable, provided, of course, that the several circuit connections are modified as required by the polarity reversal thereby involved, Moreover, it is, of course, possible to utilize a single, dual-filament lamp in substitution for the paired individual alarm indication and acknowledgement verification lamps hereinbefore described, reserving one filament exclusively to one function and the other filament to the other function. In the latter case, distinctiveness in the illumination would require steady operation of one filament andflashing operation of the other, or something equivalent, and, also, modification of intracircuit connections would be necessary, all as understood in the art, but the basic principles and circuits hereinbefore disclosed are all fully applicable.

From the foregoing, it will be understood that this invention can be varied in numerous respects within the skill of the art without departure from its essential spirit,

and it is therefore intended to be limited only within the.

scope of the appended claims.

What is claimed is:

1. An electrical annunciator circuit comprising in combination a D.-C. supply, a first electronic bistable switching branch circuit and a second electronic bistable switching branch circuit connected in parallel circuit relation: ship one to the other across said D.-C. supply, said first electronic, bistable switching circuit being provided with an alarm indication lamp together with an alarm indication control means consisting of a solid state electronic blocking means and a current-stable negative resistance switching element connected in series electrical circuit with said alarm indication lamp, said electronic blocking means having applied thereto a-fixed preselected polarity bias of magnitude such that the voltage difference between t the side of said D.-C. supply having said preselected polarity and said bias does not exceed the switching threshold of said switching element and wherein said electronic blocking means has applied to it, first, said signal signifye ing the existence of an abnormal state in a point monitored of said preselected polarity and a voltage magnitude developing a first voltage drop across said switching element exceeding said switching threshold of said switching element, thereby actuating said switching element to its ON state drawing electrical current from said D.C. supply through said first electronic bistable switching branch circuit to establish a distinctive illuminated state of said alarm indication lamp and, second, said signal signifying the restoration of said point monitored to normal state of polarity opposite from said preselected polarity and a voltage magnitude reducing the current flow through said switching element below the holding current value of said switching element, thereby actuating said switching element to the OFF state halting said drawing of electrical current through said first electronic, bistable switching branch circuit, thus disestablishing said distinctive illuminated state of said alarm indication lamp, said second electronic, bistable switching branch circuit being provided with an acknowledgement verification lamp together with acknowledgement verification lamp switch on means establishing a distinctive illuminated state of said acknowledgement verification lamp responsive to the establishment of said distinctive illuminated state of said alarm indication lamp, and manually operated means disestablishing at will said distinctive illuminated state of said acknowledgement verification lamp.

2. An electrical annunciator circuit according to claim 1 wherein said electronic blocking means is a transistor operating in the switching mode to which said signal signifying the existence of an abnormal state in said point monitored and said signal signifying the restoration of said point monitored to normal state are applied via the base element of said transistor.

3. An electrical annunciator circuit according to claim 1 wherein said alarm indication lamp control means consists of a transistor as electronic blocking means and a current-stable, negative resistance switching element connected in series electrical circuit with said alarm indication lamp, provided with signal input means consisting of an independent branch circuit made up of a series-connected resistor and single-pole, single-throw switch connected in parallel circuit relationship with said first electronic, bistable switching branch circuit and said second electronic, bistable switching branch circuit across said D.-C. supply and, via a cross connection running from a point between said resistor and said switch, to the base element of said transistor, said switch being actuated to a first uniquie position responsive to the existence of an abnormal state in a point monitored connecting said base element of said transistor in circuit with the side of said D.-C. supply having a preselected polarity and a voltage magnitude applying said signal signifying the existence of said abnormal state in said point monitored by development of a "oltage drop across said switching element exceeding said switching threshold of said switching element, so as to actuate said switching element to its ON state drawing electrical current from said D.-C. supply through said first electronic, bistable switching branch circuit thus establishing said distinctive illuminated state of said alarm indication lamp, and said switch being actuated to a second unique position responsive to the restoration of said point monitored to normal state connecting said base element of said transistor in circuit with the side of said D.-C. supply having a polarity opposite from said preselected polarity and a voltage magnitude applying said signal signifying said restoration of said point monitored to normal state by reduction of the current flow through said switching element, so as to actuate said switching element to the OFF state halting said drawing of electrical current through said first electronic, bistable switching branch circuit, thus disestarblishing said distinctive illuminated state of said alarm indication lamp.

4. An electrical annunciator circuit according to claim 1 wherein said alarm indication lamp control means consists of a diode as electronic blocking means and a current-stable, negative resistance switching element connected in series electrical circuit with said alarm indication lamp, said signal signifying the existence of an abnormal state in said point monitored is of a first preselected polarity and voltage magnitude introduced at a location in said first electronic, bistable switching branch circuit back-biasing said diode and simultaneously raising the voltage across said switching element to a level actuating said switching element to its ON state drawing electrical current from said D.-C. supply through said first electronic, bistable switching branch circuit to thereby establish said distinctive illuminated state of said alarm indication lamp, and said signal signifying the restoration of said point monitored to normal state is of a second preselected polarity and voltage magnitude introduced at a location in said first electronic, bistable switching branch circuit reducing current fiow through said switching element below the holding current value to thereby actuate said switching element to its OFF state halting said drawing of electrical current through said first electronic, bistable switching branch circuit and thus disestablish said distinctive illuminated state of said alarm indication lamp.

5. An electrical annunciator circuit according to claim 1 provided with a FirsbOn auxiliary consisting of an independent electronic, bistable switching branch circuit connected in parallel circuit relationship with respect to said first electronic, bistable switching branch circuit and said second electronic, bistable switching branch circuit across said D.-C. supply, said independent electric, bistable switching branch circuit being provided in series electrical connection with a diode, a First-On indication lamp, a current-stable, negative resistance switching element and a normally closed, manually operated First-On acknowledgement switch, said independent electronic, bistable switching branch circuit being coupled via a capacitor to said first electronic, bistable switching branch circuit and via a Zener diode connected in shunt with said switching element to a First-On clamping bus, said Zener diode providing a shunting back-circuit with respect to said switching element closed by previous unacknowledged actuation of any other First-On circuits tied to said clamping bus, and said capacitor transmitting a signal of preselected polarity and voltage magnitude responsive to said establishing of said distinctive illuminated state of said alarm indication lamp back-biasing said diode and thereby raising the voltage imposed across said switching element to a level actuating said switching element to On state drawing current through said independent electronic, bistable switching branch circuit to thereby establish a distinctive illuminated state in said First-On indication lamp subject, however, to the concomitant existence of said Zener diode in non-shunting state. i

6. An electrical annunciator circuit according to claim 1 provided with a Ring Back auxiliary consisting of an independent electronic, bistable switching branch circuit connected in parallel circuit relationship with respect to said first electronic, bistable switching branch circuit and said second electronic, bistable switching branch circuit across said D.C. supply, said independent electronic, bistable switching branch circuit being provided in series electrical connection with a current-stable, negative resistance switching element, a Ring Back indication lamp, a diode and a normally closed, manually operated Ring Back acknowledgement switch, said independent electronic, bistable switching branch circuit being coupled via a capacitor to said first electronic, bistable switching branch circuit and via a Zener diode to said second electronic, bistable switching branch circuit, said capacitor transmitting a signal of preselected polarity and voltage magnitude responsive to said disestablishing of said distinctive illuminated state of said alarm indication lamp back-biasing said diode and thereby raising the voltage imposed across said switching element to a level actuating said switching element to ON state drawing current through said independent electronic, bistable switching branch circuit to thereby establish a distinctive illuminated state in said Ring Back indication lamp subsequent to said disestablishment of said distinctive illuminated state of said acknowledgement verification lamp and the concomitant disruption of the shunting eflfect of said Zener diode inhibitory of switching action on the part of said switching element in said independent electronic, bistable switching branch circuit.

References Cited by the Examiner UNITED STATES PATENTS Re. 24,031 Re. 25,214

18 3,029,421 4/1962 Beguin 340213.1 3,081,449 3/1963 Wernlund 340213.1 X 3,084,338 4/1963 Mauer et al. 340213.1 3,098,953 7/1963 Herr. 3,107,349 10/1963 Sperry 340-2132 3,124,793 3/1964 Foster 340213.2

10 Control Engineering, December 1956 pp. 70-76.

NEIL C. READ, Primary Examiner.

ROBERT M. ANGUS, Assistant Examiner.

Claims

1. AN ELECTRICAL ANNUNCIATOR CIRCUIT COMPRISING IN COMBINATION A D.-C. SUPPLY, A FIRST ELECTRONIC BISTABLE SWITCHING BRANCH CIRCUIT AND A SECOND ELECTRONIC BISTABLE SWITCHING BRANCH CIRCUIT CONNECTED IN PARALLEL CIRCUIT RELATIONSHIP ONE TO THE OTHER ACROSS SAID D.-C. SUPPLY, SAID FIRST ELECTRONIC, BISTABLE SWITCHING CIRCUIT BEING PROVIDED WITH AN ALARM INDICATION LAMP TOGETHER WITH AN ALARM INDICATION CONTROL MEANS CONSISTING OF A SOLID STATE ELECTRONIC BLOCKING MEANS AND A CURRENT-STABLE NEGATIVE RESISTANCE SWITCHING ELEMENT CONNECTED IN SERIES ELECTRICAL CIRCUIT WITH SAID ALARM INDICATION LAMP, SAID ELECTRONIC BLOCKING MEANS HAVING APPLIED THERETO A FIXED PRESELECTED POLARITY BIAS OF MAGNITUDE SUCH THAT THE VOLTAGE DIFFERENCE BETWEEN THE SIDE OF SAID D.-C. SUPPLY HAVING SAID PRESELECTED POLARITY AND SAID BIAS DOES NOT EXCEED THE SWITCHING THRESHOLD OF SAID SWITCHING ELEMENT AND WHEREIN SAID ELECTRONIC BLOCKING MEANS HAS APPLIED TO IT, FIRST, SAID SIGNAL SIGNIFYING THE EXISTANCE OF AN ABNORMAL STATE IN A POINT MONITORED OF SAID PRESELECTED POLARITY AND A VOLTAGE MAGNITUDE DEVELOPING A FIRST VOLTAGE DROP ACROSS SAID SWITCHING ELEMENT EXCEEDING SAID SWITCHING THRESHOLD OF SAID SWITCHING ELEMENT, THEREBY ACTUATING SAID SWITCHING ELEMENT TO ITS "ON" STATE DRAWING ELECTRICAL CURRENT FROM SAID D.-C. SUPPLY THROUGH SAID FIRST ELECTRONIC BISTABLE SWITCHING BRANCH CIRCUIT TO ESTABLISH A DISTINCTIVE ILLUMINATED STATE OF SAID ALARM INDICATION LAMP AND, SECOND, SAID SIGNAL SIGNIFYING THE RESTORATION OF SAID POINT MONITORED TO NORMAL STATE OF POLARITY OPPOSITE FROM SAID PRESELECTED POLARITY AND A VOLTAGE MAGNITUDE REDUCING THE CURRENT FLOW THROUGH SAID SWITCHING ELEMENT BELOW THE HOLDING CURRENT VALUE OF SAID SWITCHING ELEMENT BELOW THE CURRENT FLOW THROUGH ING ELEMENT TO THE "OFF" STAGE HALTING SAID DRAWING OF ELECTRICAL CURRENT THROUGH SAID FIRST ELECTRONIC, BISTABLE SWITCHING BRANCH CIRCUIT, THUS DISESTABLISHING SAID DISTINCTIVE ILLUMINATED STATE OF SAID ALARM INDICATION LAMP, SAID SECOND ELECTRONIC, BISTABLE SWITCHING BRANCH CIRCUIT BEING PROVIDED WITH AN ACKNOWLEDGEMENT VERIFICATION LAMP SWITCHTOGETHER WITH ACKNOWLEDGEMENT VERIFICATION LAMP SWITCHON MEANS ESTABLISHING A DISTINCTIVE ILLUMINATED STATE OF SAID ACKNOWLEDGEMENT VERIFICATION LAMP RESPONSIVE TO THE ESTABLISHMENT OF SAID DISTINCTIVE ILLUMINATED STATE OF SAID ALARM INDICATION LAMP, AND MANUALLY OPERATED MEANS DISESTABLISHING AT WILL SAID DISTINCTIVE ILLUMINATED STATE OF SAID ACKNOWLEDGEMENT VERIFICATION LAMP.