Abstract:
A method of operating an aspirated smoke detector includes providing an ambient condition detector, establishing a first flow baseline for the detector, and, establishing a second, lower, flow baseline for the detector. A selected airflow is sampled, and determining if the airflow sample should be compared to the first flow baseline or the second flow baseline, and, responsive thereto determining if a trouble indictor should be generated.

Description:
FIELD 
       [0001]    The application pertains to control systems and methods for monitoring variable airflows which might impact operation of ambient condition detectors. More particularly, the application pertains to such systems and methods to improve operationality of aspirating smoke detectors in varying airflow environments. 
       BACKGROUND 
       [0002]    Aspirating smoke detectors are known and useful in a variety of commercial and industrial environments. When commissioned, aspirating smoke detectors establish an airflow baseline for the air that flows through the devices. During the operating life of the product the current air flow is monitored and compared to the baseline that was established during commissioning. When the current flow measurement deviates from the baseline airflow established during commissioning a trouble conditions is reported to the operator of the equipment. 
         [0003]    Aspirating smoke detectors are often used to monitor airflow on the return air grills for HVAC units. During operation HVAC units may continuously cycle on and off which can result in periods of high air flow followed by periods of stagnant air. These changes in airflow can cause an aspirating smoke detector to generate trouble conditions due to the current air flow when compared to the established baseline. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  illustrates a block diagram of a system in accordance herewith; and 
           [0005]      FIG. 2  is a flow diagram illustrating aspects of a method in accordance herewith. 
       
    
    
     DETAILED DESCRIPTION 
       [0006]    While disclosed embodiments can take many different forms, specific embodiments thereof are shown in the drawings and will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles thereof as well as the best mode of practicing same, and is not intended to limit the application or claims to the specific embodiment illustrated. 
         [0007]    In one aspect, embodiments hereof more than one baseline is established. For example a baseline for when the HVAC unit is running at its maximum velocity and a second when the HVAC unit is off, would allow the device to account for the large airflow changes and prevent false trouble conditions. 
         [0008]    The aspirating smoke detector could have an input from the HVAC unit which would indicate when the system is running and the unit could determine which airflow baseline should be used for indicating a trouble condition if such a condition exists. Example inputs could be ‘airflow on’, ‘airflow off’, input from an anemometer, etc. 
         [0009]    In yet another aspect, when initializing the device will establish two baselines, one when the HVAC unit is on and one when it is off. During normal operation the device will sample the current airflow and compare it to the appropriate baseline value. The device selects the baseline to compare the current reading to by reading the input from the HVAC unit or from an external flow monitoring sensor. 
         [0010]    If the flow varies by a percentage indicative of a trouble condition then the device will report an airflow trouble condition. 
         [0011]      FIGS. 1, 2  illustrate respectively aspects of a system  10  in accordance herewith along with a method  100 . System  10  includes an ambient condition detector  12 , which could be an aspirating smoke detector. Detector  12  includes a smoke chamber  14 , an aspirator  14   a,  smoke inflow conduits  14   b,  and smoke outflow conduits  14   c.    
         [0012]    Detector  12  is coupled to control circuits  16  by an output signal line  14   d . As those of skill will understand, the signals on line  14   d  are indicative of smoke detected in chamber  14 . 
         [0013]    The control circuits  16  can be implemented at least in part by one or more programmable processors  16   a  which can execute instructions  16   b  located at the detector  12 . 
         [0014]    A storage element  18   a  is coupled to circuits  16 , and provides storage for at least two different baseline values. Storage element  18   b  is also coupled to circuits  16  and provides storage for at least one trouble limit value. The usefulness of these stored values is discussed subsequently. 
         [0015]    A flow monitor  22  can provide output signals, on a line  22   a  indicative of sensed flow in a target area or region such as region R. Line  22   b  can couple an on/off signal for the HVAC unit indicative of when it is energized and operating to provide heat, ventilation or cooling to the region R. 
         [0016]    System  10  can operate in a variety of modes. One operational mode is illustrated in  FIG. 2  as method  100 . Initially detector  12  can be energized and reset as at  102 . A determination is made as to whether detector  12  is being put into service, or commissioned, as at  104 . If so, high air flow and low airflow baselines, indicative operating state of HVAC unit, can be established as at  106 ,  108 . Such values can be stored as discussed above in baseline store  18   a.  Optionally, a trouble limit value can be stored in unit  18   b  at this time. 
         [0017]    Subsequently, when detector  12  is placed to service a region such as region R, a current airflow is sampled, as at  110 , via a flow monitor such as  22 . A determination is made, as at  112 , as to the state of the HVAC unit. An electrical signal  22   b  indicative of this state can be coupled to control circuits  16 . This signal provides information as to whether the HVAC unit is energized, and on, or, not energized, and off. 
         [0018]    If the determination is that the HVAC unit is on, another determination is made, as at  114 , as to whether a percentage change, the trouble limit value, from the high airflow baseline exceeds the trouble limit. If so, a trouble condition is indicated, as at  116 . An indicium of this state can then be transmitted via interface  20   a  and medium  20   b  to a displaced monitoring or security location. 
         [0019]    If the HVAC unit is not on, as at  112 , a determination is made, as at  118 , as to whether the percent change, the same or a different trouble limit value, from the low airflow base line exceeds that trouble limit. If so the trouble condition is indicated, as at  116 . 
         [0020]    Those of skill will understand that neither the specific details of the exemplary system  10 , nor details of method  100  are limitations hereof excepted as described herein. If desired multiple pairs of baseline, and multiple trouble limit values can be stored in units  18   a, b  without departing from the spirit and scope hereof. 
         [0021]    From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope hereof. It is to be understood that no limitation with respect to the specific apparatus illustrated herein is intended or should be inferred. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims. Further, logic flows depicted in the figures do not require the particular order shown, or sequential order, to achieve desirable results. Other steps may be provided, or steps may be eliminated, from the described flows, and other components may be add to, or removed from the described embodiments.