Synchronization circuit for visual/audio alarms

Abstract

A strobe alarm system which includes multiple normally self-timed strobe circuits connected in a common loop to a fire alarm control panel, and a sync control circuit, which may be incorporated in the fire alarm control panel, for causing the strobes to flash in synchronism at a predetermined rate which will insure that a person viewing the multiple strobes would not see flash rates higher than the predetermined synchronized rate, which is preferably less than five flashes per second. The sync control circuit does not interfere with the supervision functions of the alarm system, and when an alarm condition is present it supplies power to the strobe circuits which it then interrupts once every flash cycle to cause a sync trigger circuit in each strobe to fire its flashtube, and to reset the internal timer of each strobe to ready it for arrival of the next sync signal. Each strobe circuit in the loop includes a resettable timer for recycling its own flash unit in a non-synchronous fail-safe mode in case the sync signal should fail to appear within a finite period following the last previous flash. That is, normally the strobes are all fired at the same time in response to sync signals applied to their sync trigger circuits, but in the event the sync signal is lacking the strobes will continue to flash, each at a rate determined by its internal timer.

We claim:  
     
       1. A control circuit for synchronously firing at a predetermined rate of plurality of flash units each of which has a timer trigger circuit which normally fires the unit independently of the others, comprising: 
       a two-conductor power distribution line to which each of a plurality of flash units is connected through a respective timer trigger circuit and through a respective sync trigger circuit connected in parallel with a corresponding timer trigger circuit;  
       a sync control circuit having input terminals connected across a D.C. power source and output terminals connected to said power distribution line, said sync control circuit comprising:  
       first controlled switching means connected in series between said input terminals and said output terminals for supplying power from said D.C. power source to said plurality of flash units when and only when an alarm condition is present ; and  
       timer means connected across said input terminals and receiving power from said D.C. power source when and only when an alarm condition is present, for actuating said first controlled switching means and briefly interrupting the supply of power to said power distribution line at said predetermined rate for producing a sync signal for causing said sync trigger circuits all to simultaneously fire its respective flash unit and for re-setting the timer trigger circuit of each flash unit to enable it to trigger the unit in the event no sync signal arrives after elapse of a predetermined period following the last previous sync signal.  
     
     
       2. A control circuit according to  claim 1 or  claim 25 , wherein said first controlled switching means comprises relay means having normally closed contacts connected between said input terminals and said output terminals, and a coil connected in series with a normally open switch across said input terminals, wherein said switch is closed at said predetermined rate by pulse signals generated by said timer circuitmeans for causing said normally closed contacts to briefly open. 
     
     
       3. A control circuit according to  claim 2 , wherein said timer circuit  means comprises a microcontroller programmed to generate pulse signals having a duration in the range from 10 to 30 milliseconds at intervals of about 2.9 seconds. 
     
     
       4. A control circuit according to  claim 1 , wherein each flash unit comprises a first capacitor connected in parallel with a flash tube across said two-conductor power distribution line, first switch means for connecting and disconnecting an inductor across said two-conductor power distribution line to store energy in said inductor during periods of connection and causing energy to be transferred from said inductor to said capacitor during periods of disconnection of said first switch means, means including optocoupler means connected across said power distribution line for repetitively cycling said first switch means between open and closed states, and wherein the timer trigger circuit includes second switch means coupled to and operable to fire a respective flashtube when the timer trigger circuit has timed out. 
     
     
       5. A control circuit according to  claim 4 , wherein each flash unit further comprises means for limiting the energy coupled from said inductor to said first capacitor to that necessary to cause firing of said flashtube with a specified brightness at a specified rate. 
     
     
       6. A control circuit according to  claim 5 , wherein said optocoupler means comprises a light-emitting diode and a transistor having base, emitter and collector electrodes, and wherein said energy-limiting means comprises a Zener diode connected between the base electrode of the optocoupler transistor to a terminal of said first capacitor and poled to cause said optocoupler to stop cycling said first switch means when the voltage on said first capacitor has attained the threshold firing voltage of said flashtube. 
     
     
       7. A control circuit according to  claim 4 , wherein said second switch means of each timer trigger circuit includes an SCR. 
     
     
       8. A control circuit according to  claim 7 , wherein each sync trigger circuit includes a first resistor and a second capacitor connected in series across a supply of D.C. voltage having an amplitude lower than that of said D.C. power source, third switch means and a second resistor serially connected across said second capacitor, and means connecting the junction between said third switch means and said second resistor to a gate electrode of the SCR included in the respective timer trigger circuit. 
     
     
       9. A control circuit according to  claim 7 , wherein the timing trigger circuit and the sync trigger circuit in each flash unit share a common timing signal generator which in the absence of sync signals generates and applies trigger pulses to the gate electrode of said SCR at a predetermined frequency for causing said flashtube to flash at a first rate, and which in response to application of sync pulses generates and applies trigger pulses to the gate electrode of said SCR at said predetermined rate. 
     
     
       10. A control circuit according to  claim 1 , wherein each flash unit comprises a first capacitor connected in parallel with a flashtube, means including first switch means for connecting and disconnecting an inductor across said power distribution line to store energy in said inductor during periods of connection and causing energy to be transferred from said inductor to said first capacitor during periods of disconnection of said first switch means, means including microcontroller means connected across said power distribution line programmed for repetitively cycling said first switch means between its open and closed states until said first capacitor is charged to the threshold firing voltage of said flashtube, 
       wherein the timer trigger circuit and the sync trigger circuit of each flash unit share a triggering circuit which includes an SCR connected in parallel with  electrically coupled to said flashtube, and  
       wherein said microcontroller means, in the absence of sync signals, generates and applies trigger pulses to a gate electrode of said SCR at a predetermined frequency for causing the flashtube to flash at a first rate, and in response to the application of sync signals generates and applies trigger pulses to the gate electrode of said SCR at said predetermined rate.  
     
     
       11. A control system for synchronously firing at a predetermined rate separate groups of flash units, each group for providing visual alarm signals to a given zone and consisting of  comprising a plurality of flash units each having an individual timing trigger circuit which normally fires independently of one another comprising: 
       for each zone, a two-conductor power distribution line to which each of the plurality of flash units included in the group is connected through a respective timer trigger circuit, and a respective sync trigger circuit;  
       a sync control circuit which includes, for each zone, first controlled switching means having input terminals connected across a D.C. power source and output terminals connected to said power distribution line for supplying power from said source to all of the plurality of flash units in the zone when, and only when, an alarm condition is present in that zone ; and  
       circuit means including a microcontroller and a power supply therefor connected to the first controlled switching means for all of said zones for supplying power to said microcontroller when, and only when, power from said D.C. source is applied to at least one group of flash units, and wherein said microcontroller is coupled to and is programmed to ascertain to which zone or zones power is being supplied and to  generate and apply to the first controlled switching means of said powered  a zone or zones a signal for actuating the same for briefly interrupting the supply of power to the power distribution line connected to the powered zone or zones and producing a sync signal for causing the corresponding sync trigger circuits to fire all of the flash units connected to the powered distribution line or lines, and for re-setting the timer trigger circuit of all of the flash units connected to the powered distribution line or lines for enabling them to trigger a respective flash unit in the event no sync signal arrives after elapse of a predetermined time period following the last previous sync signal.  
     
     
       12. A control system according to  claim 11 or  claim 26 , wherein each of said first controlled witching means comprises relay means having normally closed contacts connected between said input and output terminals, and a coil connected in series with a normally open switch across a D.C. voltage source, wherein said normally open switch is briefly closed at said predetermined rate by pulse signals generated and applied thereto by said microcontroller for causing brief opening of said normally closed contacts. 
     
     
       13. A control system according to  claim 12 , wherein said microcontroller is programmed to generate pulse signals having a duration in the range from 10 to 30 milliseconds at intervals of about 2.9 seconds. 
     
     
       14. A control circuit  system according to  claim 11 , wherein each flash unit comprises a first capacitor connected in parallel with a flashtube across said two-conductor power distribution line, means including first switch means for connecting and disconnecting an inductor across said two-conductor power distribution line to store energy in said inductor during periods of connection and causing energy to be transferred from said inductor to said first capacitor during periods of disconnection of said means, means including optocoupler means connected across said power distribution line for repetitively cycling said first switch means between open and closed states, and wherein the timer trigger circuit includes second switch means coupled to and operable to fire its respective flashtube when the timer trigger circuit has timed out. 
     
     
       15. A control circuit  system according to  claim 14 , wherein each flash unit further comprises means for limiting the energy coupled from said inductor to said first capacitor to that necessary to cause firing of said flashtube with a specified brightness at a specified rate. 
     
     
       16. A control circuit  system according to  claim 15 , wherein said optocoupler means comprises a light-emitting diode and a transistor having base, emitter and collector electrodes, and wherein said energy-limiting means comprises a Zener diode connected between the base electrode of the optocoupler transistor to a terminal of said first capacitor and poled to cause said optocoupler to stop cycling said first switch means when the voltage on said first capacitor has attained the threshold firing voltage of said flashtube. 
     
     
       17. A control circuit  system according to  claim 14 , wherein said second switch means of each timer trigger circuit includes an SCR. 
     
     
       18. A control circuit  system according to  claim 17 , wherein each sync trigger circuit includes a first resistor and a second capacitor connected in series across a supply of D.C. voltage having an amplitude lower than that of said D.C. power source, third switch means and a second resistor serially connected across said second capacitor, and means connecting the junction between said third switch means and said second resistor to the gate electrode of the SCR included in the respective timer trigger circuit. 
     
     
       19. A control circuit  system according to  claim 17 , wherein the timing trigger circuit and the sync trigger circuit in each flash unit share a common timing signal generator which in the absence of the sync signals generates and applies trigger pulses to the gate electrode of said SCR at a predetermined frequency for causing said flashtube to flash at a first rate, and which in response to application of sync signals generates and applies trigger pulses to the gate electrode of said SCR at said predetermined rate. 
     
     
       20. A control circuit  system according to  claim 11 , wherein each flash unit comprises a first capacitor connected in parallel with a flashtube, means including first switch means for connecting and disconnecting an inductor across a respective power distribution line to store energy in said inductor during periods of connection and causing energy to be transferred from said inductor to said first capacitor during periods of disconnection of said first switch means, mean including microcontroller means connected across said power distribution line programmed for repetitively cycling said first switch means between open and closed states until said first capacitor is charged to the threshold firing voltage of said flashtube, 
       wherein the timer trigger circuit and the sync trigger circuit of each flash unit share a flashtube triggering circuit which includes an SCR, and  
       wherein said microcontroller means, in the absence of sync signals, generates and applies trigger pulses to a gate electrode of said SCR at a predetermined frequency for causing the flashtube to flash at a first rate, and in response to the application of sync signals generates and applies trigger pulses to the gate electrode of said SCR at said predetermined rate.  
     
     
       21. A control system comprising two or more control systems as defined in  claim 11 or  claim 26 each for synchronously firing at a predetermined rate respective separate groups of flash units, 
       wherein the microcontroller of each of said two or more control systems includes an expansion circuit having expansion input terminals and expansion output terminals, and wherein the expansion output terminals of each are connected to the expansion input terminals of another in “daisy-chain” fashion, and  
       wherein each expansion circuit includes means for transferring sync signals from its expansion input terminals to its expansion output terminals whether or not its respective microcontroller is powered.  
     
     
       22. A control system according to  claim 21 , wherein said means for transferring sync signals when the respective microcontroller is not powered comprises relay means having normally closed contacts connected between said expansion input terminals and said expansion output terminals and a coil connected across its power supply for said microcontroller, and 
       wherein said means for transferring sync signals when the respective microcontroller is powered, and therefore energizes said relay means to open said normally closed contacts, comprises means including optocoupler means connected between said expansion input terminals and said microcontroller for receiving and forwarding any sync signals appearing on said expansion input terminals to the optocoupler means of the next successive microcontroller.  
     
     
       23. A control system for firing separate groups of flash units sequentially all within a predetermined time interval and each at a predetermined rate, each group for providing visual alarm signals to a given zone and consisting of  comprising a plurality of flash units each having an individual timing trigger circuit which normally fires the unit independently of the others, comprising: 
       for each zone, a two-conductor power distribution line to which each of the plurality of flash units included in the group is connected through a respective timer trigger circuit and a respective sync trigger circuit;  
       a sync control circuit which includes, for each zone, first controlled switching means having input terminals connected across a D.C. power source and output terminals connected to said two-conductor distribution line for supplying power from said source to all of the plurality of flash units in that zone when, and only when, an alarm condition is present in that zone ; and  
       circuit means including a microcontroller and a power supply therefor connected to the first controlled switching means for all  each of said zones for supplying power to said microcontroller when, and only when, power from said D.C. source is applied to the flash units associated with at least one zone, and wherein said microcontroller is coupled to and is programmed to ascertain to which zone or zones power is being supplied and to  generate and to sequentially apply to the first controlled switching means of each of said zones a pulse signal for actuating the same at staggered times within a predetermined time interval for briefly interrupting the supply of power, if present, to the associated power distribution line and producing a sync signal for causing the corresponding sync trigger circuits to be fired, and for re-setting the timer trigger circuit for all flash units connected to a powered distribution line for enabling them to trigger a respective flash unit in the event no sync signal arrives after elapse of a predetermined time period following the last previous sync signal.  
     
     
       24. A control system according to  claim 23 or  claim 27 , wherein said system includes four groups of flash units, and 
       wherein said microcontroller is programmed to generate four equally spaced pulse signals within an interval of about 2.9 seconds and to apply successive pulse signals each to a different one of said four groups of flash units.  
     
     
       25. A control circuit for synchronously firing at a predetermined rate a plurality of flash units of a fire alarm warning system, said system including a fire alarm control panel having a power supply for the system, comprising: 
         a two - conductor power distribution line to which each of said plurality of flash units is connected through a respective sync trigger circuit;    
       
         a sync control circuit having input terminals connected to said system power supply and output terminals connected to said power distribution line;  
       
         said sync control circuit further including  (1)  first controlled switching means electrically connected between said input terminals and said output terminals for supplying power from said system power supply to said plurality of flash units and  (2)  means connected to said input terminals and receiving power from said system power supply when, and only when, an alarm condition is present for actuating said first controlled switching means and briefly interrupting the supply of power to said power distribution line at said predetermined rate to produce sync signals at said predetermined rate; and    
       
         said sync signals being operative to simultaneously actuate the respective sync trigger circuits of said flash units and cause said strobe alarm units to flash at said predetermined rate. 
       
     
     
       26. A control circuit according to  claim 25 , wherein each flash unit comprises a first capacitor connected in parallel with a flash tube across said two- conductor power distribution line, first switch means for connecting and disconnecting an inductor across said two - conductor power distribution line to store energy in said inductor during periods of connection and causing energy to be transferred from said inductor to said capacitor during periods of disconnection of said first switch means, and means including optocoupler means connected across said power distribution line for repetitively cycling said first switch means between open and closed states.   
     
     
       27. A control circuit according to  claim 26 , wherein each flash unit further comprises means for limiting the energy coupled from said inductor to said first capacitor to that necessary to cause firing of said flashtube with a specified brightness at a specified rate. 
     
     
       28. A control circuit according to  claim 27 , wherein said optocoupler means comprises a light- emitting diode and a transistor having base, emitter and collector electrodes, and wherein said energy - limiting means comprises a Zener diode connected between the base electrode of the optocoupler transistor to a terminal of said first capacitor and poled to cause said optocoupler to stop cycling said first switch means when the voltage on said first capacitor has attained the threshold firing voltage of said flashtube.   
     
     
       29. A control system for synchronously firing at a predetermined rate separate groups of flash units, each group for providing visual alarm signals to a given zone and comprising a plurality of flash units, comprising: 
         for each zone, a two - conductor power distribution line to which each of the plurality of flash units included in the group is connected through a respective sync trigger circuit;    
       
         a sync control circuit which includes, for each zone, first controlled switching means having input terminals connected to a power source and output terminals connected to said power distribution line for supplying power from said source to all of the plurality of flash units in that zone; and  
       
       
         circuit means including a microcontroller and a power supply therefor connected to the first controlled switching means for each of said zones for supplying power to said microcontroller when, and only when, power from said source is applied to at least one group of flash units, and wherein said microcontroller is coupled to and is programmed to generate and apply to the first controlled switching means of one or more of said zones a signal for actuating the same for briefly interrupting the supply of power to the power distribution line connected to the said one or more zones and producing a sync signal for causing the corresponding sync trigger circuits to fire all of the flash units connected to the powered distribution line or lines. 
       
     
     
       30. A control system according to  claim 29 , wherein each flash unit comprises a first capacitor connected in parallel with a flashtube across said two- conductor power distribution line, means including first switch means for connecting and disconnecting an inductor across said two - conductor power distribution line to store energy in said inductor during periods of connection and causing energy to be transferred from said inductor to said first capacitor during periods of disconnection of said means, and means including optocoupler means connected across said power distribution line for repetitively cycling said first switch means between open and closed states.   
     
     
       31. A control system according to  claim 30 , wherein each flash unit further comprises means for limiting the energy coupled from said inductor to said first capacitor to that necessary to cause firing of said flashtube with a specified brightness at a specified rate. 
     
     
       32. A control system according to  claim 31 , wherein said optocoupler means comprises a light- emitting diode and a transistor having base, emitter and collector electrodes, and wherein said energy - limiting means comprises a Zener diode connected between the base electrode of the optocoupler transistor to a terminal of said first capacitor and poled to cause said optocoupler to stop cycling said first switch means when the voltage on said first capacitor has attained the threshold firing voltage of said flashtube.   
     
     
       33. A control system for firing separate groups of flash units sequentially all within a predetermined time interval and each at a predetermined rate, each group for providing visual alarm signals to a given zone and comprising a plurality of flash units, comprising: 
         for each zone, a two - conductor power distribution line to which each of the plurality of flash units included in the group is connected through a respective sync trigger circuit;    
         a sync control circuit which includes for each zone, first controlled switching means having input terminals connected to a power source and output terminals connected to said two - conductor distribution line for supplying power from said source to all of the plurality of flash units in that zone; and    
       
         circuit means including a microcontroller and a power supply therefor connected to the first controlled switching means for each of said zones for supplying power to said microcontroller when, and only when, power from said source is applied to the flash units associated with at least one zone, and wherein said microcontroller is coupled to and is programmed to generate and to sequentially apply to the first controlled switching means of each of said zones a pulse signal for actuating the same at staggered times within a predetermined time interval for briefly interrupting the supply of power, if present, to the associated power distribution line and producing a sync signal for causing the corresponding sync trigger circuits to be fired. 
       
     
     
       34. An alarm unit for use in an alarm system, comprising: 
         means for connection to a two - conductor power distribution line as the sole source of power for the alarm unit;    
         means for producing a visual alarm signal, the visual alarm signal producing means comprising a first capacitor connected in parallel with a flash tube, first switch means for connecting and disconnecting an inductor across said two - conductor power distribution line to store energy in said inductor during periods of connection of said first switch means and causing energy to be transferred from said inductor to said capacitor during periods of disconnection of said first switch means, and means for repetitively cycling said first switch means between open and closed states;    
       
         means for detecting interruptions of power to the alarm unit over said power distribution line; and  
       
       
         means for triggering the visual alarm signal producing means in response to the detection of a first interruption of power of a first predetermined duration of time. 
       
     
     
       35. The alarm unit of  claim 34 , wherein each flash unit further comprises means for limiting the energy coupled from said inductor to said first capacitor to that necessary to cause firing of said flashtube with a specified brightness at a specified rate. 
     
     
       36. The alarm unit of  claim 35 , wherein: 
         said repetitively cycling means includes optocoupler means comprising a light - emitting diode and a transistor having base, emitter and collector electrodes; and    
         said energy - limiting means comprises a Zener diode connected between the base electrode of the optocoupler transistor to a terminal of said first capacitor and poled to cause said optocoupler to stop cycling said first switch means when the voltage on said first capacitor has attained the threshold firing voltage of said flashtube.   
     
     
       37. An alarm unit for use in an alarm system, comprising: 
       
         means for producing a visual alarm signal;  
       
         means for connection to a two - conductor power distribution line as the sole source of power for the alarm unit;    
       
         means for detecting interruptions of power to the alarm unit over said power distribution line;  
       
       
         means for triggering the visual alarm signal producing means in response to the detection of a first interruption of power of a first predetermined duration of time; and  
       
       
         timer means for triggering the visual alarm signal producing means in the event no power interruption is detected within a predetermined time interval following the detection of a prior power interruption. 
       
     
     
       38. The alarm unit of  claim 37 , wherein the timer triggering means includes switch means coupled to and operable to fire said flashtube upon the expiration of said predetermined time interval. 
     
     
       39. The alarm unit of  claim 38 , wherein: 
       
         the switch means of the timer trigger means includes and SCR; and  
       
       
         the timer means for triggering the visual alarm signal producing means includes a first resistor and a capacitor connected in series across a voltage supply having an amplitude lower than that of the power supplied to the alarm unit, second switch means and a second resistor serially connected across said capacitor, and means connecting the junction between said second switch means and said second resistor to a gate electrode of said SCR. 
       
     
     
       40. The alarm unit of  claim 37 , wherein: 
       
         the visual alarm signal producing means comprises a first capacitor connected in parallel with a flashtube, means including first switch means for connecting and disconnecting an inductor across said power distribution line to store energy in said inductor during periods of connection of the first switch means and causing energy to be transferred from said inductor to said first capacitor during periods of disconnection of said first switch means, and means including microcontroller means programmed for repetitively cycling said first switch means between its open and closed states until said first capacitor is charged to the threshold firing voltage of said flashtube;  
       
       
         the timer trigger means and the means for triggering the visual alarm signal producing means in the absence of a power interruption share a triggering circuit which includes an SCR electrically coupled to said flashtube; and  
       
       
         the microcontroller means, in the absence of said power interruptions, generates and applies trigger pulses to a gate electrode of said SCR at a predetermined frequency for causing the flashtube to flash at a first rate and, in response to the detection of power interruptions, generates and applies trigger pulses to the gate electrode of said SCR. 
       
     
     
       41. An alarm unit for use in an alarm system, comprising: 
         means connectable to a two - conductor power distribution line for receiving power as the sole source of power for said alarm unit;    
       means for generating a visual alarm signal;  
         means for detecting predetermined - pattern variations in said power signal and, in response thereto, for controlling the operation of said visual alarm generating means; and    
         means for causing said visual alarm signal generating means to generate a visual alarm signal in the event a first predetermined - pattern variation in said power is not again detected within a predetermined time period following the preceding detection of said first predetermined - pattern variation in said power signal.   
     
     
       42. A sync control circuit for use in an alarm system having (1)  a fire alarm control panel with a power source,  (2)  a plurality of alarm units, and  (3)  a two - conductor power distribution line as the sole source of power for said plurality of alarm units, each of said alarm units comprising means for producing a visual alarm signal and means for triggering said visual alarm signal producing means in synchronization with all other alarm units upon receiving a sync pulse, the sync control circuit comprising:    
         a set of input terminals and a set of output terminals, the set of input terminals receiving power from said power source which is to be supplied to the alarm units over said two - conductor line;    
       
         a switching means connected between said set of input terminals and said set of output terminals; and  
       
       
         control means for actuating the switching means to interrupt power to the alarm units at a predetermined rate for producing a sync pulse to cause each alarm unit to produce a visual alarm signal simultaneously with the other alarm units in the system. 
       
     
     
       43. The sync control circuit of  claim 42 , further comprising timer means connected across said set of input terminals, and receiving power from said power source when, and only when, an alarm condition is present, for actuating said switching means and briefly interrupting the supply of power to said power distribution line at a predetermined rate for producing sync signals for causing the visual alarm signal producing means of the alarm units all to simultaneously generate visual alarm signals. 
     
     
       44. The sync control circuit of  claim 43 , wherein said switching means comprises relay means having normally closed contacts connected between said set of input terminals and said set of output terminals, and a coil connected in series with a normally open switch across said set of input terminals, wherein said switch is closed at said predetermined rate by pulse signals generated by said timer means for causing said normally closed contacts to briefly open. 
     
     
       45. The sync control circuit of  claim 44 , wherein said timer circuit comprises a microcontroller programmed to generate pulse signals having a duration in the range of from  10  to  30  milliseconds at said predetermined rate. 
     
     
       46. A control system according to any one of claims  11 ,  23 ,  29  and  33  wherein said microcontroller is further coupled to and programmed to ascertain to which zone or zones power is being supplied. 
     
     
       47. A system comprising two or more control system as defined in any one of claims  11 ,  23 ,  29  and  33 , wherein the respective sync control circuits of said two or more control systems include expansion circuits that are electrically interconnected such that signals generated by any one of said microcontrollers for actuating the first switching means of a zone or zones controlled by said one microcontroller are electrically coupled to the other one or more microcontrollers for control of the first switching means of a zone or zones controlled by said other one or more microcontrollers.