Abstract:
A hazard alarm includes: a detector for detecting a hazard parameter; trigger logic; and reset logic. The trigger logic triggers an alarm state when the measured parameter reaches a predetermined trigger threshold. The alarm state is maintained until a reset is successfully performed. The reset logic, upon a reset command, resets the alarm state if the measured parameter is below a predetermined reset threshold, and inhibits resetting of the alarm state if the measured parameter is above the predetermined reset threshold.

Description:
RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/502,335, filed Sep. 12, 2003.  
         [0002]     The entire teachings of the above application are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0003]     Conventional fire and smoke detection methods and apparatus generally include the use of well-known smoke and heat detectors, such as ionization smoke detectors and photooptical smoke detectors. These devices can be used as independent detector systems, such as those typically found in home use, or as peripheral devices reporting alarm conditions to a centralized system as is commonly used in larger buildings and in industrial use.  
         [0004]     Whether these devices are used as stand-alone systems or peripheral devices, the principle of their operation is generally the same. For example, a light-scattering type photooptical detector generally comprises a light-emitting source, such as a light-emitting diode (LED), and a light sensor, such as a photo diode, contained in a substantially light proof sample chamber having low reflectance walls. Light from the light-emitting source is reflected off the low reflectance walls to the light sensor, which is out of the direct path of light. Air surrounding the photooptical detector passes generally freely in and out of the sample chamber. When ambient air is relatively free from fire or combustion products, such as smoke, only a relatively small amount of light from the LED is reflected off the chamber walls to be detected by the light sensor. This low light receiving condition is the normal or no-alarm state in the photooptical detector.  
         [0005]     As the amount of combustion products increases, the amount of light reflected or scattered by the combustion products increases. The increased light scattering generally increases the amount of light reaching the light sensor proportionally. This phenomenon generally correlates to percent obscuration per foot. Simply put, percent obscuration per foot is a measurement of the reduction in visibility the human eye would see in a room containing combustion products.  
         [0006]      FIG. 1  is a graph  10  illustrating the typical operation of an existing alarm. The amount of light detected by the light sensor may be represented as a voltage output, for example in the range of 0 volts and 5 volts. The curve  12  represents the detector voltage output as it varies in time due to circumstances presented for exemplary purposes. As the amount of light detected by the light detector increases due to increased combustion products, the voltage output generally increases. Conventional ionization detectors also output increasing voltage as the smoke condition rises. When, at  16 , the detector voltage output reaches a predetermined alarm threshold  14 , an alarm condition is indicated by audible, visual or other indications for appropriate investigation or evacuation of the alarm area.  
         [0007]     Many home alarm detectors automatically reset at  18  when the measured parameter (the detector voltage output) again falls below the alarm threshold  14 . A small amount of hysteresis (not shown) may be provided to prevent the alarm from needlessly and annoyingly transitioning back and forth between alarm and non-alarm states when the measured parameter hovers for a time at or near the alarm threshold  14 .  
         [0008]     In other typical fire alarm operation, the alarm does not automatically reset itself, and emergency personnel must reset the fire alarm system after investigating the source of an alarm, for example, at  20 . For an alarm reset to take place, the heat and/or smoke sensor(s) must be at a reading (temperature or “% smoke obscuration”) lower than the alarm threshold  14 .  
         [0009]     For example, a 135° F. heat sensor will transition into an alarm state when the ambient temperature reaches 135° F. In the present art, a fire alarm system allows the system to reset to a normal (non-alarm) state as long as the measured parameter, at the time the reset key is pressed, is below the alarm threshold  14 . The same holds true for smoke sensors, which are rated in “% obscuration per foot.” As long as the sensor reading at reset is below the alarm threshold  14 , a fire alarm control panel will perform a reset and indicate a normal condition.  
       SUMMARY OF THE INVENTION  
       [0010]     An embodiment of the present invention can provide valuable insight to emergency responders by inhibiting an alarm reset unless a reading lower than a distinct alarm reset threshold has been obtained. Fire alarm personnel are notified that an unusual temperature or smoke level remains, and that perhaps further investigation is needed before declaring a sight “clear.” 
         [0011]     The alarm reset threshold, taken in the context of a site that has just experienced a fire alarm, is an indication that a smoldering fire may still exist, or that an unseen heat source is still present. Implementation of this feature can prevent “recalls” of fire department personnel after a flare up. Valuable time can be gained by informing these personnel that an abnormal state still exists.  
         [0012]     For example, a 135° F. heat sensor might have an alarm reset threshold of 100° F. If, upon the instigation of a system reset, for example by pressing a reset button or otherwise initiating a reset request, the alarm threshold is below 135° F. but above 100° F., a warning message is displayed or, in the case of an audio warning, a message such as a prerecorded message is announced.  
         [0013]     The alarm reset threshold may be set to a factory default, or it could be set to a level approved by a local authority. Alternatively, the alarm reset threshold may be automatically track the device&#39;s average analog value, i.e., its historic “normal” reading, with, for example, a 10% tolerance allowance.  
         [0014]     A further embodiment provides means to allow override of the latched alarm based on a command from an Emergency Responder. This would allow departure of emergency personnel should they determine that no cause for concern exists.  
         [0015]     The circuitry for implementing an alarm reset threshold, as well as the reset inhibition and override may be located on individual alarms, or on an alarm control panel, or both, according to the specific embodiment. Some embodiments may require the entry of a password before allowing an override.  
         [0016]     In accordance with the present invention, a hazard alarm includes a detector (sensor) for measuring or detecting a hazard parameter, trigger logic and reset logic. The trigger logic triggers an alarm state when the measured parameter reaches a predetermined alarm threshold. The alarm state is maintained until a reset is successfully performed. The reset logic, upon a reset command, resets the alarm state if the measured parameter is below a predetermined reset threshold, and inhibits resetting of the alarm state if the measured parameter is above the predetermined reset threshold. “Logic” may be implemented, for example, using digital hardware (circuitry) and/or software, as well as analog circuitry. The hazard parameter may an indication of, but is not limited to: heat, fire, smoke, carbon monoxide, natural gas or other measurable dangerous conditions. The alarm may be, for example, an individual alarm unit, or an alarm control panel.  
         [0017]     The inability to reset may be an indication that, for example, a smoldering fire still exists, or that an unseen heat source is present.  
         [0018]     Preferably, the alarm threshold and reset threshold are sufficiently different to prevent reset of the alarm state when an abnormal condition continues to pertain even after the measured parameter falls below the alarm threshold.  
         [0019]     An embodiment of the present invention may also include reset override logic which, when activated, overrides the reset inhibition by resetting the alarm state even if the measured parameter is not below the reset threshold.  
         [0020]     A warning presenter, such as a display, may also be included which, upon a reset command, presents a warning message if the measured parameter is not below the reset threshold  
         [0021]     In one embodiment, the reset threshold is set to a factory default. Alternatively, the reset threshold may be set to a level approved by a local authority. Yet another possibility is for the reset threshold to be set to the alarm&#39;s average analog value.  
         [0022]     Note that a measurement “upon reset” refers to a measurement taken at approximately the same time as the reset command. For example, such a measurement could be taken in response to the reset command; it could be the last previous measurement taken, or the next, or a combination of those, such as the result of the application of some formula (e.g. averaging) to several measurements.  
         [0023]     In addition, references to exceeding the threshold include embodiments in which the threshold must be surpassed, and other embodiments where simply reaching the threshold is sufficient. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0025]      FIG. 1  is a graph illustrating the voltage output of an operating conventional fire and smoke alarm and the alarm threshold.  
         [0026]      FIG. 2  is a schematic illustration of a building having peripheral detector devices interconnected with a central control panel in accordance with an embodiment of the present invention.  
         [0027]      FIG. 3  is a graph illustrating a problem presented by current art alarms.  
         [0028]      FIG. 4A  is a graph illustrating the reset threshold aspect of an embodiment of the present invention.  
         [0029]      FIG. 4B  is a graph illustrating a scenario similar to that of  FIG. 4A , wherein in addition, an Emergency Responder attempts to override the reset inhibition.  
         [0030]      FIG. 5  is a block diagram of an implementation of an embodiment of the present invention.  
         [0031]      FIG. 6  is a flowchart illustrating operation of the trigger logic of  FIG. 5 .  
         [0032]      FIG. 7  is a flowchart illustrating operation of the reset logic and message presenter of  FIG. 5 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]     A description of preferred embodiments of the invention follows.  
         [0034]     Referring to  FIG. 2 , the preferred alarm detection system according to the present invention comprises a plurality of peripheral sensors or detectors DET. 1, DET. 2 . . . DET. N which may be located at strategic positions in a building or other structure where fire or smoke detection is desired. These peripheral devices are connected via communication lines as illustrated in  FIG. 2  for preferably centralized control and monitoring of the peripheral devices in a control panel CP. One such peripheral device/control panel communication system is disclosed in U.S. Pat. No. 4,796,025, the specification of which is incorporated herein by reference.  
         [0035]      FIG. 3  is a graph  30  illustrating a problem presented by current art alarms. In this example, a heat sensor with an alarm threshold  14  at 135° F. senses a temperature, e.g., 140° F., in excess of its alarm threshold  14 . The building is evacuated and emergency personnel respond. They find a heat source, extinguish it, and believe the danger has been eliminated. In this scenario, however, they have found only part of the problem. An unseen fire still smolders behind a wall.  
         [0036]     The sensor soon measures a lower temperature, say 130° F. Even though 130° F. is far from a normal temperature, currently existing sensors normally allow an unconditional successful system reset  20 . Emergency personnel are falsely reassured that the danger is gone. They leave, and later the fire reinitiates. The temperature rises and triggers the alarm at  22 , but by that time, emergency personnel have left.  
         [0037]     An embodiment of the present invention may prevent this or similar scenarios by implementing an alarm reset threshold. In the above example, an alarm reset threshold set to some value below 130° F. (as according to an embodiment of the present invention) would have inhibited the system from being reset.  
         [0038]     An embodiment of the present invention thus can indicate that current temperature or smoke is still above normal levels, even though the absolute reading is below the alarm threshold. System resets are inhibited, and the alarm remains latched until the temperature or smoke sensor reports a reading significantly below the alarm threshold. That is, the system has a different setting for restore/reset than for alarm.  
         [0039]      FIG. 4A  is a graph  40  illustrating the reset threshold aspect of an embodiment of the present invention. As in  FIGS. 1 and 3 , the measured parameter  12  (e.g., the detector output voltage) rises until, at  16 , it crosses the alarm threshold  14 , causing an alarm state. At  20 , the visible fire has been put out, the temperature (or whatever parameter is being measured) has been reduced significantly, and the Emergency Responder presses the reset button or otherwise attempts to initiate an alarm reset.  
         [0040]     Now, however, the measured parameter value  12  is still above the reset threshold  42 . The request/command to reset the system is thus inhibited. A message such as “Warning-System Reset Aborted. Heat Sensor Reports Temperature is 125° F.,” may be displayed or announced. A similar message for a smoke detector alarm might be “Warning-System Reset Aborted. Smoke Sensor Reports x% Smoke Still Present.” 
         [0041]     Later, at  44 , the Emergency Responder again presses the reset button. This time, the measured parameter value  12  is below the reset threshold  42 , and the system is reset, reverting to a normal state.  
         [0042]      FIG. 4B  is a graph  50  illustrating a scenario similar to that of  FIG. 4A , except that at  46 , the Emergency Responder attempts to override the reset inhibition by, for example, pressing the reset button again, after a warning has been displayed or announced as discussed above, or by way of another example, by pressing a dedicated override button, or via some other means as would be readily understood by one skilled in the art. Here, the measured parameter value  12  is still above the reset threshold  42  but below the alarm threshold  14 . The override is accepted, and the system is reset, reverting; to a normal state.  
         [0043]      FIG. 5  is a block diagram of an implementation of an embodiment of the present invention. A detector/sensor  51  senses the measured parameter and provides the value  12  to the trigger logic  53  and the reset logic  55 , each of which can alter the state  57  of the system or unit.  
         [0044]     The trigger logic  53  examines the measured parameter value  52  and the alarm threshold  14  to determine whether to assert an alarm state. Once an alarm state is asserted, it is latched; that is, the system does not revert back to a normal state without a reset command.  
         [0045]     The reset logic  55 , upon a reset command  61  or an override command  63 , compares the measured parameter value  52  with the reset threshold  42  (and in the case of the override command, with the alarm threshold  14  as well) to determine whether to reset the system to a normal state, or to inhibit the request. On inhibiting a reset command  61  or an override command  63 , a message enunciator or presenter  59  may display a warning message on a display device  65  or, alternatively, announce a pre-recorded or synthesized voice message on a speaker  67 .  
         [0046]     Note that although the various components of  FIG. 5  are shown as discrete components, many of the functions may in fact be performed within a single component. Furthermore, each function may be implemented in software, hardware, or a combination, and may further be implemented using digital or analog technologies, or a combination therein. That is, the term “logic” includes, but is not limited to, digital hardware (circuitry) and/or software, as well as analog circuitry.  
         [0047]      FIG. 6  is a flowchart  100  illustrating operation of the trigger logic  53  of  FIG. 5 . At step  101 , the detector  51  ( FIG. 5 ) senses the measured parameter and provides a value  12 . At step  103 , the trigger logic  53  compares the measured value  12  with the alarm threshold  14 . If the measured parameter value  12  is greater than the alarm threshold  14 , then the alarm state is asserted and latched (step  105 ).  
         [0048]      FIG. 7  is a flowchart  200  illustrating operation of the reset logic  55  and message enunciator  59  of  FIG. 5 . At step  201 , a reset command is initiated. At step  203 , the measured parameter value  12  ( FIG. 5 ) is compared with the reset threshold  63 . If the measured parameter value  12  is less than the reset threshold  63 , then the system is reset, reverting to a normal state (step  205 ).  
         [0049]     If, on the other hand, the measured parameter value  12  is greater than the reset threshold  63 , the system is not reset, i.e., reset is inhibited, and a warning message is displayed or announced (step  207 ). If an override command is then initiated (step  209 ), then the override command is implemented and, at step  205 , the system is reset, reverting to a normal state.  
         [0050]     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.  
         [0051]     For example, in the examples presented above, an alarm state is asserted when the measured parameter value is greater than the alarm threshold. One skilled in the art would recognize that, equivalently, for certain kinds of parameters and measurements, an alarm state might be asserted when the measured parameter value is below the alarm threshold. In this case, of course, the reset threshold would be higher than the alarm threshold.  
         [0052]     In addition, it should be understood that it some embodiments, an alarm is asserted or a reset enacted or inhibited when the measured value exceeds the respective threshold. In other embodiments, the alarm is asserted or a reset enacted or inhibited when the value reaches, i.e., equals, the respective threshold. The language of the claims herein is meant to cover both cases.