Abstract:
A method and apparatus is provided for activating a carbon monoxide detector. The method includes the steps of the carbon monoxide detector measuring a current carbon monoxide level, the carbon monoxide detector comparing the current carbon monoxide level with a first threshold value, determining whether the current carbon monoxide level exceeds the first threshold value, entering an alarm state upon detecting that the current carbon monoxide level exceeds the first threshold value after a first predetermined time period, determining from memory whether the carbon monoxide detector had previously been in an alarm state before activation and upon detecting that the current carbon dioxide level does not exceed the first threshold and the carbon monoxide detector was previously in the alarm state, resuming the alarm state after a second predetermined time period.

Description:
FIELD 
       [0001]    The field of the invention relates to fire detection devices and more particularly to carbon monoxide detectors. 
       BACKGROUND 
       [0002]    Devices for detecting fires are generally known. Smoke detectors are one example of such devices. 
         [0003]    Fire detectors have found wide use in the home, office and industrial settings. As originally provided, most smoke detectors were battery powered with an audible alarm provided as an output to warn occupants of fires. 
         [0004]    In the context of large buildings, including both offices and industrial setting, fire detection devices are connected to a central alarm panel. In this context, each of the fire detection devices is monitored by the central panel. 
         [0005]    In addition to monitoring the fire detectors, the central panel may also activate visual and audible annunciators on or in the area of each of the devices. This is important were a fire is detected by a detector in one area, but it is important to provide a fire alert throughout the building or other protected areas in order to expedite the evacuation of the area. 
         [0006]    More recently, municipalities have also begun to require the use of carbon monoxide detectors in buildings. This requirement has been motivated because improperly installed, maintained and/or ventilated fuel burning appliances can produce toxic carbon monoxide that cannot be detected through other means, such as smoke detectors. 
         [0007]    However, carbon monoxide detectors do not operate the same way as smoke detectors. As such, carbon monoxide detectors cannot be mixed within a single standard zone type of an alarm system. Accordingly, a need exists for better ways of integrating the two technologies. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a block diagram of a fire alarm system in accordance with an illustrated embodiment of the invention; and 
           [0009]      FIG. 2  is a set of start up steps that may be performed by the carbon monoxide detectors of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0010]      FIG. 1  is block diagram of a fire detection system  10  shown generally in accordance with an illustrated embodiment of the invention. Included within the system  10  may be a control panel  12  and a number of fire detection devices  14 ,  16  that operate to detect fires within a protected area. The fire detection devices  14 ,  16  may include a mix of smoke detectors  14  and carbon monoxide detectors  16 . 
         [0011]    As shown in  FIG. 1 , the fire detection devices  14 ,  16  may be electrically coupled to the panel  12  by first and second conductors  32 ,  34 . In the two wire system of  FIG. 1 , the two conductors  32 ,  34  function to supply power from the panel  12  to the detectors  14 ,  16  as well as couple alarm signals from the detectors  14 ,  16  back to the alarm panel  12 . 
         [0012]    One of the difficulties with prior art fire detection systems is that those systems could not easily mix smoke detectors and carbon monoxide detectors within a single zone. Carbon monoxide detectors and other types of fire detectors such as smoke detectors are generally not mixed in the same alarm zone because the information provided by each type of device represent a different type of risk and may be used differently in assessing danger. 
         [0013]    Carbon monoxide detectors are required to indicate alarm at a threshold level of 10% COHb. This threshold is a function of time and concentration. Carbon monoxide detectors perform a very different function than smoke detectors. Because carbon monoxide detectors and smoke detectors perform different functions, and are required to send separate and distinct signals back to the control panel, they cannot be mixed within a single, conventional alarm zone connected to the alarm panel. 
         [0014]    Because of the greater chance of false alarms, smoke detectors are not normally used with carbon monoxide detectors within the same zone in two-wire alarm systems. Smoke detectors are not normally used with carbon monoxide detectors in such cases because if an alarm is received, it may not be possible to determine if the detected event was based upon smoke or carbon monoxide. 
         [0015]    Moreover, even if it can be determined that an alarm is based upon carbon monoxide, carbon monoxide is tasteless and odorless. In systems with many carbon monoxide detectors, it may not be possible to determine which carbon monoxide detector caused the alarm. 
         [0016]    In order to address these issues, the system  10  uses carbon monoxide detectors  16  that can be reset from the central control panel  12  and that use a programmed delay upon reactivation that is dependent upon carbon monoxide levels. In this way it is possible to reduce or eliminate the difficulty in troubleshooting the sources of reported alarms in the system  10 . 
         [0017]    Included within the carbon monoxide detectors  16  may be one or more programmed processors  18 ,  20  operating under control of one or more programs  24 ,  26  loaded from a non-transitory computer readable medium (memory)  22 . In this regard, a programmed, carbon monoxide detection processor  18 ,  20  may be programmed to continuously measure a carbon monoxide level via a carbon monoxide sensor  28 . The carbon monoxide detection processor  18 ,  20  may integrate carbon monoxide readings over time based upon an appropriate time versus concentration process. 
         [0018]    It should be noted that under this process, the carbon monoxide detection processor  18 ,  20  may simultaneously integrate on a number of different concentration levels in order to eventually issue a carbon monoxide alarm to the panel  12 . The carbon monoxide detector  16  may transmit the signal to the alarm panel  12  by pulling or otherwise clamping the supply voltage imposed on conductors  32 ,  34  by the alarm panel down to a predetermined value as an indication of the alarm state. 
         [0019]    For example, the carbon monoxide detection processor may include a number of carbon monoxide concentration levels (e.g., a, b, c, where a&gt;b&gt;c) and a respective threshold time value (e.g., d, e, f) associated with each level, where the time value (e.g., d) associated with concentration level a is much shorter than the time value (e.g., e) associated with concentration level b which is, in turn, shorter than the time value (e.g., f) associated with concentration level c. 
         [0020]    For example, if the concentration level should exceed level c, then a first integrator may integrate on the longest level c. If the concentration should then exceed level b, then a second integrator begins to integrate on the second level b at the same time as the first integrator continues to integrate on the first level c. 
         [0021]    Each of the integrators has a threshold time associated with the integrator. In the above example, if the concentration level should fall below concentration level b before the second integrator goes into alarm, then the second integrator is reset. Should the concentration level remain above c, then the first integrator continues to integrate. If the first integrator reaches the time threshold level associated with concentration level c without the concentration level falling below c, then the first integrator sends an alarm message to a programmed alarm processor  18 ,  20 . The alarm processor  18 ,  20  sends an alarm to the alarm panel  12 . 
         [0022]    Upon receipt of an alarm, the alarm panel  12  may issue an audible alarm through an audible alarm transducer  30 . The audible transducer  30  may be coupled across the conductors  32 ,  34  or be located inside one or more of the fire detectors  14 ,  16 . 
         [0023]    To activate the alarm transducer, the panel  12  may remove and reverse the voltage imposed on the conductors  32 ,  34 . For example, the voltage imposed on the conductors may be some appropriate supply voltage (e.g., 12 volts). To activate the alarm transducers  30 , the alarm panel may remove the imposed voltage of 12 volts and re-impose a reverse voltage of −12 volts. 
         [0024]    The removal of the imposed supply voltage (and the re-imposing of the reverse voltage) functions to temporarily deactivate the carbon monoxide detectors  16 . However before complete deactivation, a programmed deactivation processor  18 ,  20  detects the falling supply voltage and performs a number of steps before the deactivation processor  18 ,  20  is rendered inoperative by the declining voltage. For example, the deactivation processor  18 ,  20  saves a set of operating parameters present within the carbon monoxide detector  16  at the instant of shut down within memory  22 . Once of the parameters saved is whether or not the carbon monoxide detector  16  was in an alarm state at shut down. Other parameters saved include the time values of each integrator at that instant. 
         [0025]    The alarm transducers  30  may continue to sound until it is reset by a human operator through a reset button on the panel  12 . Upon activation of the reset button, the alarm panel may impose the normal operating voltage on the conductors  32 ,  34  to reactivate the fire detectors  14 ,  16 . 
         [0026]    Upon reactivation of the carbon monoxide detector  16 , a programmed start up processor  16 ,  18  retrieves the previous operating parameters from memory  22 . The start up processor  16 ,  18  may also follow a set of start up steps  100  shown in  FIG. 2 . 
         [0027]    A first step  102  performed during power on reset is to reinitialize the programmed processors  18 ,  20 . The second step  102  is to read a current carbon monoxide (CO) level from the sensor  28 . 
         [0028]    A third step  106  performed by the start up processor  18 ,  20  is to compare the current CO reading with a first start up threshold (e.g., 350 ppm). If the current CO reading exceeds the start up threshold, then the start up processor may activate a timer associated with the start up threshold. Associated with the timer and start up threshold may be a start up delay that is independent of any time values discussed above in conjunction with the integrators. At the end of the start up delay, if the current CO reading is above the start up threshold, then the CO detector  16  automatically re-enters  108  the alarm mode. 
         [0029]    On the other hand, if the start up processor  18 ,  20  determines that the current CO reading is less than the start up threshold, then the start up processor  18 ,  20  retrieves  110  the previous set of operating parameters saved in memory  22 . Next, the start up processor  18 ,  20  determines  112  whether the CO detector  16  was in an alarm state during the previous shut down. 
         [0030]    If the CO detector  16  was not in an alarm state before the previous deactivation, then the start up processor  16 ,  18  re-starts  114  the integrators using the previous readings (e.g., integrator time values) that had been saved during shut down. This causes the CO detector  16  to continue operating as if the CO detector  16  had not been shut down. 
         [0031]    On the other hand, if the detector  16  had been in an alarm state during the previous deactivation, then the start up processor  18 ,  20  activates a second start up timer that retards  116  re-entry of the CO detector  16  into the alarm state. Associated with the second start up time may be a fixed time period that allows time for a human operator of the system  10  to clear the alarm (e.g., by opening windows, doors, etc.). Alternatively, the fixed time period may be obtained by resetting the time periods associated with each of the integrators. 
         [0032]    In general, the process of  FIG. 2  provides a method for resetting the CO detectors  16  of the system  10  without retrofitting the panel  12  with additional software that would otherwise be required by CO detectors  16 . This allows the CO detectors  16  to be easily added to existing system  10  without concern for the difficulty associated with resetting most CO detectors. 
         [0033]    A specific embodiment of method and apparatus for incorporating carbon monoxide detectors into fire systems has been described for the purpose of illustrating the manner in which the invention is made and used. It should be understood that the implementation of other variations and modifications of the invention and its various aspects will be apparent to one skilled in the art, and that the invention is not limited by the specific embodiments described. Therefore, it is contemplated to cover the present invention and any and all modifications, variations, or equivalents that fall within the true spirit and scope of the basic underlying principles disclosed and claimed herein.