Abstract:
An alarm system which incorporates a large number of ambient condition sensors makes a determination as to the existence of a predetermined alarm condition by detecting respective ambient conditions from each member of a group of sensors. The indicators from the plurality of sensors are each raised to a respective predetermined exponent and summed together. The resultant sum is compared to a predetermined threshold to determine whether or not the alarm condition is present. The detectors can be spaced apart from one another in a selected region and coupled to a central control unit by a bi-directional communications link. Running averages of sums can be formed to provide filtering or smoothing or trend analysis.

Description:
FIELD OF THE INVENTION 
     The invention pertains to systems for determining the presence of a selected condition based on a plurality of data inputs. More particularly, the system pertains to a fire detection system which receives inputs from a large number of detectors or sensors which are spaced apart from one another in one or more regions of interest. 
     BACKGROUND OF THE INVENTION 
     Various systems are known for the detection of alarm conditions. One particular form of such a system is a smoke or fire detecting system for a type generally illustrated in previously issued Tice et al. U.S. Pat. No. 4,916,432. 
     Upon receipt of inputs from a plurality of sensors a control unit associated with this system is able to make a determination as to whether or not a fire condition is present in one or more regions of interest. A variety of techniques have in the past been used for purposes of making this determination. 
     One known technique has been to compare one or more of the outputs of one or more sensors to one or more preestablished thresholds. The use of multiple thresholds permits the evaluation of trend information from one or more detectors. 
     Detection systems are evolving and are able to support larger numbers of sensors, 600 to 800 sensors or more. In this environment, it becomes desirable and important to be able to analyze outputs from large numbers of detectors at a relatively high rate so as to provide timely information as to trends as well as actual alarm conditions. 
     It is also desirable to be able to assess potential alarm conditions without having to make a large number of measurements over a period of time with respect to some or all of the sensors. In addition, it would be desirable to be able to analyze and determine the presence or absence of an alarm condition from a large number of detectors without substantially increasing the cost of the associated control unit. 
     Thus there continues to be a need for methods and systems of analyzing data received from large numbers of detectors. 
     SUMMARY OF THE INVENTION 
     In accordance with the invention, a method of detecting a predetermined condition using a plurality of spaced apart ambient condition sensors includes the steps of: 
     sensing ambient conditions associated with at least some members of the plurality and producing an indicium of each sensed condition; 
     collecting the indicia at a common location; 
     forming a group of selected indicia; 
     processing the group, including raising each member of the group to an associated predetermined exponent and summing exponentially raised indicia to form a result; and 
     using the result to detect the predetermined condition. 
     In another aspect of the invention, an apparatus usable with a large number of detectors or sensors to detect a predetermined condition based on measurements made at a plurality of detectors includes a control unit. A communications link is coupled to the control unit and extends therefrom. 
     A plurality of spaced apart sensors is coupled to the link. Each member of said plurality is capable of producing an indicium representative of an adjacent ambient condition. Each sensor is capable of communicating ambient condition indicating indicia to the control unit. 
     The control unit includes a storage element for storing at least some of the indicia. The control unit includes circuitry for raising at least some of the indicia to associated predetermined exponents and summing the exponentially raised indicia to form a result. The result is then compared to a predetermined value to determine if the condition is present. 
     In yet another aspect of the invention, the sums can be added together to form a running average. The trend exhibited by the average can be used to determine whether or not an alarm condition exists. 
     Alternately, sums can be formed for one or more groups of detectors or sensors. The sums formed over a period of time from each of the groups could be directly combined. Alternately, the slopes of the sums can be determined for each of the groups and used to determine the presence of a fire condition. 
     These and other aspects and attributes of the present invention will be discussed with reference to the following drawings and accompanying specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a block diagram of a system in accordance with the present invention; 
     FIG. 2 is a flow diagram illustrating a method which embodies the present invention; and 
     FIG. 3 illustrates performance characteristics of systems in accordance with the present invention for varying members of detectors. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiment in many different forms, there is shown in the drawing, and will be described herein in detail, specific embodiments thereof with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the specific embodiments illustrated. 
     FIG. 1 illustrates a block diagram of a system 10 in accordance with the present invention. The system 10 includes a control unit 12 which can be implemented with a programmable processor 14 and a storage unit 16. The storage unit 16 can include both control programs and data storage for use by the processor 14. 
     The control unit 12 is coupled by bi-directional communication lines 20 to a plurality of ambient condition sensors or detectors generally indicated at 22. The members of plurality 22, such as sensor 22a, 22b, up to 22n are intended to detect a particular ambient condition in an adjacent region. 
     Representative-types of sensors include ionization-type or photoelectric-type smoke detectors. Temperature sensors as well as PIR-type detectors could also be used with a system in accordance with the present invention. 
     The members of the plurality 22 can be spaced apart on a floor of a building or can be spaced apart on a plurality of different floors if desired. For control and sensing purposes, as is well known, it may be desirable to define subgroups within the plurality 22 which have some particular association, such as a subgroup including all detectors on a particular floor of a building. 
     In accordance with the present apparatus and method, at a predetermined time, the detectors of the plurality 22, or a predefined subgroup thereof, are commanded by the control unit 12 to sense an adjacent ambient condition and generate a respective indicium therefor. The collective indicia from the members of the plurality 22, or the respective subgroup thereof, are then transferred to the control unit 12. 
     The indicia received at the control unit 12 are processed and each is raised to a respective, predetermined exponential value. The exponential values associated with respective detectors need not be the same. 
     The exponential values can for example, be integer values of 2 or more. It will be understood however, that the present apparatus and method are not limited to integer exponential values. 
     The values of indicia which have been raised to the predetermined exponential value are then summed to produce a result. Summing can include subtraction of various terms. For example, outputs from PIR units, indicating the presence of living people or animals in the respective region, can be used to reduce the sum. 
     The result can be compared in the control unit 12 to a predetermined value. Hence the system will indicate an alarm where: 
     
         D.sub.1.sup.x.sbsp.1 +D.sub.2.sup.x.sbsp.2 +D.sub.3.sup.x.sbsp.3 . . . +D.sub.n.sup.x.sbsp.n ±D.sub.n+1.sup.x.sbsp.n+1 ≧Threshold Value 
    
     where D i  is a value received from detector &#34;i&#34; and x i  is an associated exponent. 
     If the sum exceeds the value, the control unit 12 can proceed on a basis that the predetermined condition has been sensed and is present in the region associated with either the plurality 22 or a respective subgroup thereof. 
     The sums, determined over a period of time, can be used to form a running average. Alternately, the slope or slopes can be calculated to make an alarm condition determination. 
     FIG. 2 illustrates of the steps of a method which embodies the present invention. In an initial step 100, power is applied to the system 10. Each of the sensors such as the sensor 22a can be initialized in a step 102. 
     Subsequently, a processing sequence is entered. In the processing sequence each subgroup of the defined plurality of sensors 22 can be treated separately. In a step 106, each of the members of a selected subgroup is directed by the control unit 12 to read or sense the respective ambient condition. The sensed values are then returned to the control unit 12. 
     In a step 110, the control unit 12 raises each of the returned values to a respective predetermined exponent. The exponential values can be different from one detector to another or from one detector type to another. 
     In a step 112, each of the exponentially increased values associated with the given subgroup is added together to form a result. In a step 114, the sum can be compared to one or more predetermined thresholds. If the sum exceeds the respective threshold, a respective alarm can be generated. 
     The process can then be repeated for another subgroup or the same subgroup for purposes of smoothing or averaging. It will be understood that the use of running averages or determination of slopes to make a fire determination comes within the spirit and scope of the present invention. 
     It will be understood that other pre-alarm, local alarm, and full system alarm levels are possible as well as a choice of different exponential values. 
     Many variations on the use of the multi-device method can give good system performance. For example, it is possible to lower the pre-alarm level for a small number of devices if it becomes a function of the number of devices in a group by the following equation: 
     
         PRE-ALARM if SUM&gt;(0.1+0.15*(N-1)/N)*NF where NF (noise factor)=1 for normal systems and 2 for noisy systems. N=number of devices 
    
     It will be understood that the type of sensor or detector of the plurality 22 is not a limitation of the present invention. For example, the system 10 can be a fire detection system and the members of the plurality 22 can be heat or fire detectors. Alternately, some or all of the members of the plurality 22 could be gas detectors. 
     In the following discussion, several examples are discussed in more detail for purposes of explaining the operation and features of the system 10 and not for purposes of limiting the claimed invention. It will be understood that the particular details of processing the sensed ambient condition values and raising same to predetermined exponential value are also not a limitation of the present invention. 
     In the present example, outputs from a group of sensors are received. The received values are assigned values of 0-1. Zero is clear air, 1 is the alarm level. The returned outputs are squared. The squared values are summed to form a result. 
     The sum of the squared values must exceed a threshold value before the system will alarm. The squaring function gives inherently higher weight to higher analog values from individual sensors. 
     Table 1 illustrates minimum values necessary to alarm the system for different numbers of sensors or detectors. The alarm threshold is 1 and the detectors base output values 0-1. 
     
                       TABLE 1______________________________________   SENSOR VALUES                SUM OF SQUARES______________________________________1 SENSOR: 1.0                      1.002 SENSORS:     1.0   .4                 1.16     .8    .6                 1.003 SENSORS:     1.0   .4                 1.16     .8    .6                 1.00     .6    .6    .6           1.084 SENSORS:     1.0   .6                 1.16     .8    .6                 1.00     .6    .6    .6           1.08     .6    .6    .6   .6      1.045 SENSORS:     1.0   .4                 1.16     .8    .6                 1.00     .6    .6    .6           1.08     .6    .6    .6   .6      1.04     .6    .4    .4   .4  .4  1.00______________________________________ 
    
     To minimize false alarms, where there is more than 1 sensor, two sensors must have values of at least level 2 before the system will alarm. Otherwise, a pre-alarm can be given. Any one device can be above the alarm threshold and the system will only give a pre-alarm if all other devices in the group are below level 2. 
     Any value greater than 1 is clamped to 1 for the sum of squares method. A test condition may produce a received value of 1.40, for example, but would still be limited to 1.00. 
     The method operates on the principle that if many sensors are simultaneously increasing in value, then a fire is alarmed even though a single sensor has not reached its individual alarm threshold--as long as certain minimum conditions are met. This provides an important predictive characteristic. 
     For example, with 2 sensors an alarm will be generated if one detection is level 0.8 (80% of alarm) and another level 0.6 (60% of the alarm). But if 6 sensors are used in the group, then the alarm is determined if one sensor is level 0.6 (60%) and at least four other sensors are level 0.4 (40%) or greater. 
     Values can be returned from detectors as a percent of alarm value. By altering a preset alarm level a given detector or type of detector can be given a different weight since the returned percent values will also be altered for a given ambient condition. 
     The graphs of FIG. 3 illustrate some possibilities of system performance with the present method for various numbers of sensors. 
     From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of the invention. It is to be understood that no limitations 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.