Patent Publication Number: US-6222456-B1

Title: Detector with variable sample rate

Description:
FIELD OF THE INVENTION 
     The invention pertains to ambient condition detectors. More particularly, the invention pertains to photoelectric-type smoke detectors with variable sample rates. 
     BACKGROUND OF THE INVENTION 
     Smoke detectors have been extensively used to provide warnings of potential or actual fire conditions in a region being monitored. Photoelectric-type smoke detectors sample the contents of a smoke chamber intermittently. 
     Known photoelectric detectors sample the smoke chamber at a first rate in a quiescent state. In the event that a smoke sample exceeds a preset threshold, the sample rate is increased. If the level of smoke exceeds a threshold for several additional samples, an alarm condition will be indicated. 
     While known detectors do provide a variable sample rate, it is only in response to the presence of a predetermined smoke density. It would be desirable to be able to vary the rate even for low levels of smoke density without requiring the excessive power that can be required to operate continuously at a relatively high sample rate. Preferably such added functionality could be achieved without any significant increase in either cost or manufacturing complexity. 
     SUMMARY OF THE INVENTION 
     A detector samples an ambient condition at a predetermined rate. Circuitry in the detector analyzes the sampled values as they are being received. If the values meet a predetermined profile, such as a profile of a developing fire, the sampling rate is increased. 
     In one aspect, the circuitry recognizes the presence of a predetermined profile based on processing samples from an ambient condition sensor. For example, if three amplitude values in a row consecutively increase, the sample rate can be increased. If four sampled amplitudes in a row consecutively increase, the sample rate can again be increased. 
     Recognizing a pre-established profile and increasing the sample rate in response thereto provides additional benefits. Other processing such as smoothing of the sampled values to eliminate uncorrelated noise or carrying out other forms of preliminary processing will be accelerated due to the increased sample rate. 
     Yet another benefit of the present apparatus and process is that the average power consumption of the respective detector is only increased when the likelihood of a condition to be detected has increased. In systems having large numbers of detectors, the ability to reduce average power or current is particularly advantageous. 
     In yet another aspect, other recognizable profiles which can be used to produce increased sample rates include increased gradient values of the sampled amplitudes or the value of an integral of the sampled amplitudes. An alternate way in which a sample rate modifying profile can be established is to incorporate a second, different sensor into the detector. 
     The output signal from the second sensor can be processed. If a selected profile is recognized, the sample rate of the primary sensor can be increased. 
     Hence, where a selected profile has been recognized, the sample rate will be increased. If the profile is no longer being recognized, perhaps due to changing ambient conditions, the sample rate can be returned to its quiescent value. As a result, average power consumption will be reduced. 
     In yet another aspect, a detector can include multiple sensors. These multiple sensors can include a fire sensor or a non-fire sensor as a second sensor. In the case of more than one fire sensor, the sampling rate would increase if more than one fire sensor is giving an indication of a fire condition. In the case of the non-fire sensor, the sampling rate of the fire sensor would not increase or would decrease if the non-fire sensor is giving an indication of a non-fire condition. 
     A particular detector could include a photo-electric, optical, type sensor and an ionization sensor. These are normally sampled at a 5 second rate. Methods of implementing variable sampling for this example are: 
     a. if either sensor senses a potential fire condition, then the sampling interval of both the optical sensor and the ionization sensor will be decreased to 2.5 seconds; or 
     b. if the optical sensor senses a potential fire condition, the sampling interval of the ionization sensor will be decreased to 2.5 seconds. This reverse situation results in decreasing the sampling interval of the optical sensor; or 
     c. if both sensors sense a fire condition, then the sampling interval of both sensors will be decreased to 2 seconds (Otherwise, the sampling intervals are unchanged); or 
     d. if neither sensor senses a potential fire condition, then the sampling interval will be increased to 7.5 seconds. 
     Alternately, the sampling rate could increase linearly with the level of indication of the sensed condition. For example the sample interval could be shortened from a 5 second interval, with no indication, to a 4 second interval with a mild indication, to a 3 second interval with a stronger indication. Finally, the interval can be reduced to a 2 second interval with a very strong indication. 
     The rate is alterable by downloading different values into the detectors from a common control unit. The common control unit may determine that other devices are sensing a condition and set the remainder of the system or certain other devices to increase their sampling rate. 
     In yet another aspect, where the sampled signal is processed or filtered, both the sampling rate and the processing can be altered in response to a recognized fire profile. For example, where a predetermined profile has been recognized: 
     a) the sampling rate can be increased, (and the interval decreased) and the type of filtering changed or the degree of filtering decreased—both promote a faster response; or 
     b) the sampling rate can be increased—to promote a faster response—without altering the type or degree of filtering—thereby providing more information and a greater discrimination of a developing ambient condition; or 
     c) where there are two sensors, if one sensor is responsive to nuisance or false alarm causing conditions, the sampling rate of both sensors could be increased along with increasing the filtering of one or both sensor outputs to minimize false alarms. 
     Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and the embodiments thereof, from the claims and from the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a system in accordance with the present invention; 
     FIG. 2 is a block diagram of an ambient condition detector useable with the system of FIG. 1; 
     FIG. 3 is a graph illustrating processing of signals from detector of the type illustrated in FIG. 2; 
     FIG. 4 is a block diagram of an alternate form of the detector usable with the system of FIG. 1; 
     FIG. 5A illustrates raw sensor output and a filtered output corresponding thereto plotted as a function of time; 
     FIG. 5B illustrates the effects of increasing the sample rate using the same degree of filtering as was the case of the graph of FIG. 5A; and 
     FIG. 5C illustrates the effects of combining increased sample rate with additional processing to provide a higher degree of fire discrimination than is the case with the response of FIG. 5A but in the same time interval. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     While this invention is susceptible of embodiment in many different forms, there are 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 system  10  which can be used for monitoring a plurality of conditions in one or more regions to be supervised. The system  10  includes a common control unit  12  which could be implemented as one or more interconnected programmed processors and associated, prestored instructions. 
     The unit  12  includes an interface for coupling, for example, to a communications medium  14 , illustrated in FIG. 1 for exemplary purposes only as an optical or electrical cable. Alternately, the system  10  can communicate wirelessly, such as by RF or infrared, via transceiver  16 , illustrated in phantom in FIG. 1, and antenna  16   a.    
     Coupled to medium  14  is a plurality of ambient condition detectors  18  and a plurality of control or function units  20 . It will be understood that the relative arrangement of the members of the pluralities  18  and  20  relative to the medium  14  is not a limitation of the present invention. The members of the plurality  18  can include intrusion sensors, position sensors, gas sensors, fire sensors such as smoke sensors, thermal sensors or the like, and gas sensors, all without limitation. The members of the plurality  20  can include solenoid actuated control or function implementing units, display devices, printers or the like. 
     Where system  10  incorporates a wireless communications medium, a plurality  22  of wireless units could be in bidirectional communication with transceiver  16 . The plurality  22  can include, without limitation, ambient condition detectors, as noted above as well as control or function implementation devices without limitation. 
     Also coupled to the control unit  12  via a medium  24 , illustrated for example as a pair of electrical cables, is a plurality  26  of output devices. These could include audible or visible output devices without limitation, speech output devices and the like. The devices  26  are intended to broadcast a message, which might indicate alarm condition, in one or more predetermined regions. 
     FIG. 2 illustrates in block diagram form an exemplary member  18   n  of the plurality  18 . The member  18   n,  an ambient condition detector, includes an ambient condition sensor  40 . 
     The sensor  40  can include without limitation a smoke sensor such as a photo electric sensor, ionization sensor, gas sensor, humidity sensor or the like. Output from the sensor  40 , on a line  40   a  is coupled to profile detection circuitry  42 . 
     In a quiescent operating state, the sensor  40  can be intermittently energized at a quiescent rate to provide a sampled output on the line  40   a.  Alternately, signals on the line  40   a  can be sampled at the quiescent rate. 
     Profile detection circuitry  42  is a intended to analyze the output from sensor  40 , line  40   a  to establish the presence of a possible alarm condition (for example, a possible fire condition or a possible hazardous gas condition) even before a preset threshold, such as a pre-alarm condition, is crossed. When an appropriate profile has been detected by circuitry  42 , sampling rate determination circuitry  46 , coupled to profile detection circuitry  42 , alters, by increasing, the sampling rate of the signal on the line  41   a.  The sampling rate thus goes from the quiescent rate to a predetermined higher rate. 
     Altering of the sampling rate can be achieved by incorporating into circuitry  46  analog circuitry such as voltage controlled oscillators or digital circuitry such as counters and the like all without departing from the spirit and scope of the present invention. It will also be understood that other forms of sampling rate altering circuitry also fall within the scope of the present invention. Circuitry  46  can intermittently energize sensor  40  or it can provide gating signals to the signal on the line  40   a,  all without departing from the spirit and scope of the present invention. 
     By means of circuitry  46 , since the sampling rate of signals from sensor  40  can be increased in response to the detection of a potential alarm condition, response of the detector  18   n  to the ambient condition being sensed will be speeded up. In addition, average power required for the detector  18   n  will be reduced since in the absence of a detected profile, detector  18   n  operates at a lower sampling rate, thus conserving energy. 
     Profile detection circuitry and sampling rate determination circuitry  42 ,  46  are coupled to local control circuitry  48 . Control circuitry  48  can in turn control the operation of signal processing circuitry  50  which can provide various types of pre-processing or filtering of signals from sensor  40  prior to coupling those signals via interface circuitry  52  to either medium  14  or wireless transceiver  52   a.    
     It will further be understood that processing circuits  50  can be implemented wholly or in part in detector  18   n  as well as wholly or in part in common control unit  12  without departing from the spirit and scope of the present invention. One form of pre-processing is disclosed in Tice et al U.S. Pat. No. 5,736,928, assigned to the assignee hereof, entitled Pre-Processor Apparatus and Method and incorporated herein by reference. Three sample processing, so called min-three processing is described and illustrated therein. 
     The processed outputs on line  50   a  could in addition be coupled to the comparators  54   a, b.  It will be understood that the comparators  54   a, b  could be implemented in hardware or software at the detector  18   n.  Alternately, that functionality can be provided at common control unit  12 . 
     Where sensor  40  is intended to detect the presence of a fire condition, pre-alarm comparator  54   a  compares processed sensor output, line  50   a  to a pre-alarm threshold  54   a - 1  so as to provide an early indication of the presence of a possible fire condition. In addition, processed sensor output is compared in comparator  54   b  to an alarm threshold  54   b - 1  which is indicative of the presence of a substantial enough indication of a fire that an alarm, which could be given via members of the plurality  26 , should be provided. It will be understood that other variations are possible beyond the pre-alarm threshold and alarm threshold illustrated in FIG. 2, all without departing from the spirit and scope of the present invention. 
     Since the profile detection circuitry  42  is intended to address a developing ambient condition, various analysis approaches can be implemented. One profile can be based on a rate of change of sensor output signals. For example, circuitry  42  can detect the presence of increasing amplitude values on the line  40   a.  This rate can be compared to a preset rate. Where amplitude values on the line  40   a  assume a random distribution, no profile of interest is present. Hence, a relatively long quiescent sample interval, on the order of six seconds can be established. 
     In the event that the signal on the line  40   a  exhibits increasing amplitude for three successive sample values, the sample interval can be reduced from six seconds to two seconds irrespective of the amplitude value on the line  40   a.  Similarly, if desired, if the amplitude increases for four successive samples, the sampling interval can be decreased from 2 second intervals to one second intervals. As a result, the processing circuits  50  will receive samples at a substantially higher rate. These samples will then be analyzed either at the detector  18   n  or at the common control unit  12  to determine the presence of an alarm condition. 
     It will be understood that other types of profile detection can be used without departing from the spirit and scope of the present invention. For example, the sensor output signal can be integrated over time or averaged to create a profile. 
     FIG. 3 includes a graph which illustrates the above processing where the profile detector  42  responds to three successive increasing amplitude values on the line  40   a.  As illustrated in FIG. 3, where the output on line  40   a  from sensor  40  exhibits random values, in a two second through 20 second time period, a quiescent sample rate having six second intervals is used. At 26 seconds, a preliminary potential fire profile is detected by circuitry  41  in response to detecting three increasing amplitude values in a row. At 26 seconds, the profile detection circuitry  42  causes the sampling rate determination circuitry  46  to switch from a six second interval to a two second interval. 
       51   a  illustrates processed output values on the line  50   a  on the assumption that the sample rate has not increased.  51   b  illustrates process sample values on the line  50   a  in response to a shortened sample interval. The processing circuitry  50 , for example, carries out the type of min-three processing described in the above identified Tice et al patent that was incorporated by reference. 
     As illustrated in FIG. 3, as a result of having increased the sample rate at 26 seconds, the processed values on the line  50   a  graph  51   b  cross the prealarm threshold PR TH  sooner than do those of graph  5 l a  where the sampling rate has not been increased. Similarly, the processed signals on the line  50   a  cross the alarm threshold AL TH  sooner than is the case without increasing the sample rate. Hence, not only do the present apparatus and process result in a lower power requirement a since during quiescent periods the sample rate for the respective detectors is reduced, but they also produce shorter response intervals due to a higher sample rate when the ambient condition being detected begins to change. Using a higher sample rate, once a preliminary fire profile has been detected, takes advantage of a greater probability of the presence of an actual fire as reflected by that preliminary profile. 
     It will be understood that the circuitry  42  through  50  and  54   a, b  of FIG. 2 could be implemented wholly or in part via a programmed processor  56  (illustrated in phantom) in the detector  18   n.    
     FIG. 4 illustrates an alternate form of a detector  18   p  in accordance herewith. Detector  18   p  incorporates first and second ambient condition sensors  60   a,    60   b.  Sensor outputs on respective lines  62   a  and  62   b  are coupled to profile detection circuitry  64 . 
     In the detector  18   p,  the profile detection circuitry utilizes signals on the line  62   b  to establish the sampling rate for sensor  60   a.  Circuitry  64  uses samples on the line  62   a  to establish a sampling rate for sensor  60   b.    
     Profile determination circuitry  64  is in turn coupled to rate determination circuitry  66   a, b  for the respective sensors,  60   a  and  60   b.  Outputs from sensors  60   a, b  can in turn be coupled to processing circuitry  68 , of the type discussed in the above noted Tice et al patent, and then transmitted via interface circuitry  70  to medium  14  or via transceiver  70   a,  wirelessly, to control unit  12 . 
     For example, profile determination circuitry  64  via rate determination circuitry  66   a, b  can establish in a clear air or quiescent condition a five or six second sample interval. If, for example, sensor  60   a  is an optical-type smoke sensor and  60   b  is an ionization-type smoke sensor, increasing detected levels of smoke represent a potential fire condition. Variable sampling via circuitry  66   a, b  can be implemented as follows: 
     if either sensor  60   a,  or  60   b  provide an output to the profile determination circuitry  64  which corresponds to a potential fire profile, the sampling rate of both sensors  60   a,    60   b  can be increased by reducing the sampling interval from on the order of five to six seconds to on the order of two and one-half to three seconds. Alternately, if neither sensor produces signals which are indicative of a developing fire profile, circuitry  64  in combination with rate determination circuitry  66   a, b  will ultimately reduce the sampling rate by increasing the sampling interval to on the order of seven and one-half or eight seconds. 
     It will be understood that profile detecting circuitry  64  can detect a rate of change of a sensor input to establish the presence of a predetermined profile. Alternately, detection circuitry  64  could implement any other form of a fire profile without departing from the spirit and scope of the present invention. 
     FIGS. 5A-5C illustrate the results of changes in the processing when the sampling rate is increased. This is an example of performance of a smoke detector but it can apply, without limitation, to any other type of ambient condition detector. 
     The graph of FIG. 5A illustrates processed output: 
     
       
         output( t )=output( t− 1)*0.5 +RAW ( t )*0.5 
       
     
     when the sampling rate is NOT increased. (RAW(t)is the unprocessed signal from a smoke sensor). The output takes the shape of a step function. The final values reach 550 at 60 seconds. 
     The graph of FIG. 5B illustrates the output when processed using the above equation except the sampling rate is increased by 5. The output now has higher resolution and takes a better shape indicating a fire profile but still has spikes that are out of profile. The final values reach over 600 at 60 seconds. 
     The graph of FIG. 5C illustrates the introduction of additional processing (min 3 ) of the processed output when the sampling rate is increased. The min 3  processing removes the spikes from the processed “output” signal that results from the above noted filtering process. A strong fire profile is present in the min 3  processed output signal. 
     The added processing has improved the ability to discriminate a fire from a nuisance when the sampling rate is increased. The values still exceed 550 at 60 seconds, thus not significantly compromising the response time of FIG.  5 A. As illustrated, changing the processing method when the sampling rate is changed can dramatically improve the overall performance. 
     Changing of the processing method in conjunction with an altered sampling rate can be as simple as changing the type or degree of filtering or can be implemented by adding new routines where the processing is carried out via software based commands. 
     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 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.