Patent Publication Number: US-2021166670-A1

Title: Power control for piezo sounder

Description:
BACKGROUND 
     Fire alarm and mass notification systems are used to notify the public of the presence of fire, smoke and other potentially harmful conditions. A notification appliance circuit (NAC) may be part of such a system and include many notification devices powered and controlled by a common source and control panel. 
     A notification appliance may include a notification horn that generates a sound at predetermined intervals with a predetermined acoustic pattern. The notification appliance is typically rated at the lowest sound output and the highest input current across its specified working input voltage range. The sound output may increase in response to increasing input voltage. However, the increased sound output is typically not utilized for rating the notification appliance. Accordingly, any increase in current beyond that required to provide the lowest sound output is not efficient. Manufacturers are continually seeking to improve efficiencies in the manufacture and operation of notification appliances. 
     SUMMARY 
     A method of powering a sounder according to an exemplary embodiment of this disclosure includes, among other possible things, providing a constant input current and regulating an input voltage to a phase of a sound engine corresponding with the acoustic signal generated by a sound engine. 
     In a further embodiment of the foregoing method, regulating a sound output of the sound engine to a constant volume. 
     In a further embodiment of any of the foregoing methods, input current is stored in an energy store responsive to the sound engine being between phases. 
     In a further embodiment of any of the foregoing methods, sounds are not generated between phases. 
     In a further embodiment of any of the foregoing methods, the sound engine draws energy from both the constant input current and the energy store when generating sound. 
     In a further embodiment of any of the foregoing methods, a power control decreases the input voltage delivered to the sound engine to reduce a sound level generated by the sound engine. 
     In a further embodiment of any of the foregoing methods, the power control selects from one of a several input voltage levels to provide a corresponding acoustic signal at a corresponding volume. 
     In a further embodiment of any of the foregoing methods, the ramp rate of voltage is varied to correspond with a sound pattern. 
     A notification appliance according to another disclosed exemplary embodiment, includes among other possible things, a sound engine generating a sound according to an acoustic pattern and a power control regulating input voltage to the sound engine that is matched to the acoustic pattern. 
     In a further embodiment of the foregoing notification appliance, the sound engine generates sound when voltage is input. 
     In a further embodiment of the foregoing notification appliances, including an energy store and an input current to the power control is constant and when the sound engine is not generating sound the input current charges the energy store. 
     In a further embodiment of any of the foregoing notification appliances, the energy store provides energy to the sound engine when generating sound. 
     In a further embodiment of any of the foregoing notification appliances, the power control regulates the input voltage to the sound engine to provide a constant volume. 
     In a further embodiment of any of the foregoing notification appliances, the power control is configurable to adjust a sound level generated by the sound engine. 
     In a further embodiment of any of the foregoing notification appliances, the power control is configurable to select between one of several input voltage levels to provide a corresponding sound level. 
     In a further embodiment of any of the foregoing notification appliances, the power control is configurable to adjust a voltage ramp rate to match an acoustic pattern. 
     A notification appliance circuit (NAC) according to another disclosed exemplary embodiment, includes among other possible things, a plurality of notification appliances connected by circuit wiring to provide electric power, wherein at least one of the plurality of notification appliances includes a sound engine generating a sound according to an acoustic pattern, and a power control regulating input voltage from the to the sound engine that is matched to the acoustic pattern. 
     In a further embodiment of the foregoing NAC, the power control includes an energy store and wherein an input current from the NAC to the power control is constant and when the sound engine is not generating sound the input current charges the energy store and the energy store provides energy to the sound engine when generating sound. 
     In a further embodiment of any of the foregoing NACs, the power control is configurable to adjust a sound level generated by the sound engine. 
     In a further embodiment of any of the foregoing NACs, the power control is configurable to select between one of several input voltage levels to provide a corresponding sound level. 
     In a further embodiment of any of the foregoing NACs, the power control is configurable to adjust a voltage ramp rate to match an acoustic pattern 
     Although the different examples have the specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
     These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example notification appliance circuit (NAC). 
         FIG. 2  is a block diagram of a portion of a notification appliance. 
         FIG. 3  is a group of graphs illustrating an example acoustic pattern. 
         FIG. 4  is a block diagram of a power control for a notification appliance. 
         FIG. 5  is a group of graphs representing electrical inputs and sound output of the notification appliance. 
         FIG. 6  is a graph illustrating input voltages for different sound patterns. 
     
    
    
     DETAILED DESCRIPTION 
     Fire alarm and mass notification systems are used to notify the public, such as occupants of a building or campus, of the presence of fire, smoke and other potentially harmful conditions. It may be appreciated that in case of fire or other event likely to trigger use of the alarm or mass notification system, it is desirable to output sound likely to attract the attention of those within range of a notification appliance such as a sounder or horn. 
     Referring to  FIG. 1 , a notification appliance circuit (NAC)  10  includes a control panel  12  that receives power from an AC power source  14 . The control panel  12  powers and controls a plurality of notification appliances  24  connected by a two wire circuit  18   a ,  18   b  and a termination resistor  20 . The control panel  12  may also receive power from a backup power supply  16 . The control panel  12  provides power and control signals for operation of the notification appliances  24 . While the example NAC  10  includes three notification appliances  24 , other numbers of notification appliances could be utilized and contemplated with the context of this disclosure. Each of the example notification appliances  24  include a power control  22  that controls power supplied to a sound engine  28  and a sound temporal pattern generator  38 . 
     Referring to  FIG. 2  with continued reference to  FIG. 1 , a portion of an example notification appliance  24  is schematically shown and includes the sound engine  28  that receives a driver current  55  and driver voltage  128  from the power control  22 . The sound engine  28  includes a transducer driver  30 , an electro-acoustic transducer  32  and an acoustic chamber  34  that outputs a generated sound spatial pattern  36 . The generated sound spatial pattern  36  is the sound as would be heard based on a location and orientation relative to the notification appliance  24 . The transducer driver  30  excites a piezo diaphragm and receives sound control information  35  from the sound temporal pattern generator  38 . The electro-acoustic transducer  32  is the piezo diaphragm and converts electrical energy into mechanical movement and acoustic energy. Although a piezo diaphragm is disclosed as an example, a sound generator of any known configuration may be utilized and is within the contemplation of this disclosure. 
     The sound temporal pattern generator  38  includes a temporal code generator  40 , an acoustic roughness module  42  and a tone generator  44  that supplies the sound control information  35  to the transducer driver  30 . The temporal pattern generator  38  generates the control information  35  utilized by the transducer driver  30  to produce sounds of different frequencies for different alarm sound patterns. A sound pattern selector  124  provides a signal  122  to the temporal code generator  40  and the power control  22 . The sound pattern selection signal  122  is selected by an installer at the time of installation of the appliance  24 . Selection of the signal  122  can be made by selecting one position of a four position switch to select between two sound patterns and at least two levels of sound power. It should be appreciated that other selection mechanisms could be utilized and are within the contemplation of this disclosure, including but not limited to mechanical mechanisms, and remote wireless or hardwired electronic mechanisms. 
     The example pattern generator  38  creates signals for generating sounds of different frequencies and patterns including a temporal code (T3) that provides a fire alert sound pattern. One example fire alert sound pattern provides a sound for ½ second followed by no sound for ½ second that is repeated 3 times followed by a delay of 1 second, than repeated. The temporal pattern generator  38  may also instruct a general alarm tone. The T3 temporal code is disclosed and explained by way of example, however, other temporal patterns could be utilized within the contemplation and scope of this disclosure including a temporal pattern that provides a Carbon Monoxide (CO) detection alert sound pattern commonly referred to as T4. 
     The temporal pattern generator  38  includes the acoustic roughness module  42  that generates a modulation of the sound produced that is intended to enhance the ability of the output sound pattern  36  to attain the attention of those being warned. 
     Referring to  FIG. 3  with continued reference to  FIG. 2 , the purpose of the sound engine  28 , and the output sound pattern  36  is to attract the attention of those within range. Accordingly, a sound waveform is selected that is effective to alert those within range. One model for the sound waveform is the human scream that provides a certain depth and amplitude modulation that is known to be effective at attracting attention. The amplitude modulation utilized to generate the desired sound is referred to as the acoustic roughness. In this disclosed example, the acoustic roughness provides a modulation frequency of around 50 Hz 
     The graphs shown in  FIG. 3  show the underlying signals that generate the acoustic roughness for a fire alert sound pattern  72 . The fire alert sound pattern  72  is shown in the graph indicated at  64  where three periods of sound  68  of ½ second each are generated between ½ second intervals  66  of no sound. The six periods  68  and  66  are followed by a delay  70  of one second and then repeated again. Graphs  74 ,  78  and  80  zoom in on one period  68  to show the smallest increments of actuation utilized to generate each period  68 . Each of the periods  68  comprise a number of higher frequency bursts indicated at  76  in graph  74 , and at an increased zoom in graph  78 . The bursts  76  are further generated by tones  84  shown in graphs  78  and shown in expanded form in graph  80 . Power indicated at  88  in graph  86  is consumed by the electro-acoustic transducer  32  only during the generation of tones. 
     The power control  22  receives a power control signal  45  from the tone generator  44  that predicts generation of the driver current  55  that powers the sound engine  28 . The power control  22  also receives the sound pattern selection signal  122 . Power to generate the sound pattern  36  is provided from the input current  15  from the NAC  10 . 
     If the sound engine  28  is configured to produce a sound at a volume that corresponds with the input voltage  126  from the NAC  10 , then any rise or change in the input voltage  126  from the NAC  10  would cause a corresponding increase in sound. Accordingly, the input voltage  126  from the NAC  10  would control the volume of the sound output from the sound engine  28 . As the sound power output from the sound engine  28  varies, so would the current input  15 . Performance of the notification appliance  24  is determined utilizing defined conditions such as input voltage and is utilized for comparison to other appliances and as a means of selecting appliances when designing and planning a NAC. The sound output and input current of the notification appliance at the defined conditions are known as that appliances rating. One example rating records a minimum sound and a maximum current across their specified operating voltage range for the appliances  24 . The value of the minimum sound and maximum current is identified as the rating for the appliance  24 . The ratings for each appliance  24  are used as comparison to other appliances. As appreciated, an efficient appliance minimizes the rated current required to provide the rated sound output. Sound output above the minimum sound output is not beneficial to the rating. Accordingly, increases in the input current  15  that result in a sound level above the minimum sound output level is a waste of current. 
     Referring to  FIG. 4 , with continued reference to  FIGS. 2 and 3 , the example power control  22  includes features that control the sound output from the sound engine  28  and enable a constant and lower input current  15 . The power control  22  decouples the sound output from the NAC  10  voltage  126  by regulating a driver voltage  128  to the sound engine  28  to match a phase of a sound control  35 . The power control  22  includes voltage regulator functionality in the power controller  114  that produces a current control signal  112  that is used to regulate the charging current  110  communicated to the energy store  46  from a current controller  48 . The energy store  46  integrates the charging current  110  to provide a driver voltage  128  and driver current  55  to the sound engine  28 . The energy store  46  provides a charge level signal  116  to the power controller  114  for use in a feedback loop for determining the current control signal  112 . 
     Referring to  FIG. 5 , with continued reference to  FIG. 4 , the example power control  22  keeps the input current  15  constant by adjusting the current control signal  112  to maintain the driver voltage  128  at a phase  134  ( FIG. 5 , graphs  56 A and  56  B) of the voltage level selected by the sound pattern selection signal  122 . Graph  56 A and  56 B are of the same input voltage  58  shown in different scales to show the small variation and corresponding high and low points that correspond with the sound shown in graph  50 . In this example the phase  134  is selected to be synchronous with the transition between no sound and sound shown as phase  132  of graph  50 , however, the phase  132  could by any other arbitrary phase of the sound signal level cycle  130 . The phase  132  is synchronized to the power control single  45 . Adjustment of the current control signal  112  is accomplished by known methods including feed-forward, proportional integral derivative, or proportional integral controller. 
     The disclosed input current  15  is therefore constant within recognized variations which may be due to factors such as manufacturing tolerances of components, temperature variations for any one appliance, and differences in temperature between several different appliances. Additionally, the disclosed example constant input current  15  may also include variations that are present due to a dither between discrete levels provided as part of a digital signal. Moreover, the example constant input current  15  may include any additional variations that are present in any electrical device that are otherwise understood to provide a constant input current. 
     Referring to  FIG. 5  with continued reference to  FIGS. 2 and 4 , during continuing operation (not at startup) the power controller  114  senses driver voltage  128  through its analog the charge level signal  116  and determines a phase  134  based upon power control signal  45 . At startup the power controller  114  tailors the input current to achieve ramp rates as described below, and takes initially as input a startup control signal from the startup controller  120  (initially the charge level signal  116  will be close to 0, and will ramp up as charging levels increase). The power controller  114  regulates a selected phase  134  of the driver voltage  128  by adjusting charging current  110  from the current controller  48  through the current control signal  112 . Graph  50  illustrates sound pulses  57  that are provided at period  130 . Each sound pulse  57  is output for a defined duration 54 followed by an interval of no sound  52 . The power controller  114  regulates voltage  58  at a phase  134  shown on graphs  56 A and  56 B to correspond to the sound level phase shown on graph  50  at  132 . 
     The drive voltage  128  to the transducer driver  30  is illustrated in graphs  56 A and  56 B and shown as  58 . When the transducer  32  is not generating sound, it does not require energy and the current  15  flowing from the NAC  10  is stored in the energy store  46  ( FIG. 4 ). Storage of energy in the energy store  46  increases the charge level  116  of the energy store  46 . When the transducer  32  is active and generating sound as shown in graph  50 , the sound engine  28  receives energy from the input current  15  along with the energy stored in the energy store  46  when the transducer  30  was not sounding. By buffering energy in the energy store  46  during intervals  52 , the input current  62  shown in graph  60  is kept constant and creates a small ripple in the energy store charge level voltage  58  shown in graph  56 A. 
     The power controller  114  is programmable to provide phased regulation of the input voltage  58  to the transducer driver  30 . The example input voltage  58  is phase matched to the acoustic pattern shown in graph  50 . In this example, the voltage is regulated to a phase just prior to the generation of sound indicated at  57  in graph  50 . 
     The example power control  22  is programmable to set sound power level for a specific application. A notification appliance  24  may need to operate at a reduced volume to accommodate smaller areas and rooms. The use of a resistor to dissipate energy does not provide an optimal decrease in input power and may therefore waste power. The example power control  22  is adjusted to reduce the input voltage  58  to provide the reduced sound power. In one disclosed example, the power controller  114  is programmable at the time of installation to provide several volume settings by reducing the piezo driver input voltage  58 . The volume settings can be implemented during installation to match volume to a specific location of installation. The selection can be with a selector switch or through other known means. The power control  22  may also be programmed at the manufacturing and design stage to provide modifications to sound output based on each sound pattern and sound-power combination. In one example, an input voltage  58  can be reduced for intermittent sound patterns as compared to the input voltage  58  utilized for continuous sound patterns. For example, the fire alert pattern  72  may require less sound power as compared to a continuous-high sound pattern. 
     Referring to  FIG. 6  with continued reference to  FIGS. 2 and 4 , the notification appliance  24  is rated according to current during a running condition and during startup. During startup energy stores are charged to a predefined level prior to generation of a sound. A single fixed ramp rate at a single fixed current for all sound patterns wastes energy for all but the highest sound levels. The example power control  22  tailors the input current to provide different voltage ramp rates for each sound pattern. By varying the voltage ramp rates, the startup current can be maintained below the running current to provide improved current ratings. The control of charging the energy store  46  during startup is by the startup controller  120 , as different from the temporal pattern generator  38  which controls the charging of the energy store during running conditions. 
     The example graph  90  illustrates control of the input current  15  by the power control  22  to tailor the voltage ramp rates  96 ,  98 ,  100  and  104  to a corresponding sound pattern. Graph  90  illustrates the running voltage and ramp-rate for different sound patterns. The example ramp-rate is between 7 and 75 volts/second. In another example, the ramp-rate may be between 1 and 110 volts/second. Moreover, it is within the contemplation of this disclosure that the ramp-rate maybe between 0.1 and 1000 volts/second. The voltage indicated at  92  corresponds with a continuous sound pattern with a high sound level  92 . The voltage indicated at  94  corresponds with a continuous sound pattern with a low sound level  94 . The voltage indicated at  102  corresponds with a fire alert sound pattern at high sound level. The voltage indicated at  106  corresponds with a fire alert sound pattern at a low sound level. Continuous sound levels may require a faster start time and therefore the voltage ramp-rates may be higher. 
     The start-time for the fire alert sound patterns may be lower and therefore the voltage ramp rates for these sound levels are reduced to reduce the corresponding running current rating. In this example, each voltage  92 ,  94 ,  102  and  106  include different ramp rates  96 ,  98 ,  100  and  104  that corresponds to the each individual sound pattern. By tailoring the voltage ramp rate to the power needs of each sound pattern, each of the sounds can be rated at the running current instead of a higher startup current needed for only one sound pattern. 
     The disclosed example appliance  24  includes a power control  22  that utilizes less current by controlling and matching the input voltage to the sound pattern. Control of the input voltage relative to the desired acoustic pattern and shunting current to an energy store  46  when not generating a sound enables the input current to be lower and quasi-constant to provide an overall decrease in current use by the notification appliance. 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this disclosure.