Abstract:
An environmental abnormality detecting apparatus for detecting abnormality in atmosphere such as heat, smoke, and a gas. A sampling circuit is provided for periodically sampling analog signals from a detector for detecting these phenomena. A quantizer quantizes sampled signals with step levels. An accumulator having a plurality of counters provides different accumulation times corresponding to the step levels. Reliability in accumulation effect is not degraded, and an abnormality signal can be detected in a short period of time when a degree of abnormality is high.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an environmental abnormality detecting apparatus for detecting an analog signal representing an abnormality in smoke, heat, gas or the like and producing an alarm. 
     An accumulator type fire detector is one type of conventional smoke detector for detecting a fire which has been proposed wherein analog smoke signals are accumulated in an accumulator and the fire detector is started when an accumulation level exceeds a predetermined level so as to improve reliability. However, according to this conventional fire detector, even if a level of the analog signal is extremely high, it takes a long period of time to operate the fire detector, resulting in inconvenience. An example of such a conventional accumulator type fire detector is described in U.S. Pat. No. 3,872,449, incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     The present invention eliminates this conventional drawback, and has as its object to provide a highly reliable environmental abnormality detecting apparatus which immediately produces an alarm when an analog signal has a high level, but in which the effect of an accumulator is not degraded. 
     In order to achieve the above object of the present invention, there is provided an environmental abnormality detecting apparatus as claimed in claim 1 which comprises: a detector for detecting analog information representing changes in environmental factors such as smoke, heat and gas and for converting the analog information to an electrical analog signal; a sampling circuit for sampling analog signals from the detector after every predetermined time interval; a quantizer for converting an output signal from said sampling circuit to a stepwise signal and for generating a plurality of outputs in units of step levels; and accumulating means having different accumulation times for the respective step levels of the quantizer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an environmental abnormality detecting apparatus according to the present invention; 
     FIG. 2 is a graph showing operating characteristics of the apparatus of FIG. 1 in comparison with those of a conventional apparatus; and 
     FIGS. 3A and 3B are flow charts for explaining signal processing of the apparatus shown in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An environmental abnormality detecting apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. 
     FIG. 1 is a block diagram of the environmental abnormality detecting apparatus according to this embodiment. The detecting apparatus detects smoke concentration by a light-scattering effect and hence a fire. This detecting apparatus comprises: a light-emitting element 8 such as a light-emitting diode for emitting light in a region of interest for smoke detection; an oscillator 1 for intermittently driving the light-emitting element 8; a light-receiving element 9 arranged in a structure which does not receive direct light from the light-emitting element 8 but receives only light scattered by smoke; an amplifier 2 for properly amplifying to a given magnitude a detection signal generated from the light-receiving element 9; a plurality of comparators 3-1 to 3-n for respectively comparing the output from the amplifier 2 with a plurality of comparison step voltages E1 to En; a plurality of 2-input NAND gates 4-1 to 4-n for receiving the output from the oscillator 1 and the output signals from the comparators 3-1 to 3-n; a plurality of counters 5-1 to 5-n, reset in response to the outputs from the 2-input NAND gates 4-1 to 4-n, for counting the number of pulses of the output signals from the comparators 3-1 to 3-n and for generating high level (to be referred to as an H hereinafter) signals from output terminals Q thereof when counts of the respective counters 5-1 to 5-n have reached different predetermined values, respectively; and a multi-input OR gate 6 for receiving a plurality of signals from the output terminals Q and generating a smoke detection signal which appears at an output terminal 7. 
     The operation of the environmental abnormality detecting apparatus having the arrangement described above will now be described. The oscillator 1 generates pulses at a predetermined period T to intermittently drive the light-emitting element 8. The pulse signal from the oscillator 1 sets the input terminals of the plurality of 2-input NAND gates 4-1 to 4-n at an H level. In a normal condition, i.e., when no smoke is present, an output voltage e from the amplifier 2 is lower than all the comparison voltages E1 to En. In this case, all the outputs from the comparators 3-1 to 3-n are set at the H level. Signals of the H level are respectively supplied to the 2-input NAND gates 4-1 to 4-n. Outputs from the 2-input NAND gates 4-1 to 4-n are set at low level (to be referred to as an L hereinafter), so that the counters 5-1 to 5-n are reset. 
     By way of simplicity, assume that the comparison voltages E1 to En satisfy the relation E1&gt;E2&gt; . . . &gt;En, and that the counters 5-1 to 5-n generate H signals when counts of the counters 5-1 to 5-n are 2 1 , 2 2 , . . . , and 2 n . When a smoke concentration is relatively low and the output voltage e from the amplifier 2 satisfies the inequality En-1&gt;e&gt;En, only the counter 5-n is enabled. When this state is maintained longer than an accumulation time t (t=2 n  ·T), the output from the counter 5-n goes to the H level. A detection signal of the H level then appears at the output terminal 7 through the multi-input OR gate 6. When a smoke concentration is high and the output voltage e from the amplifier 2 exceeds the comparison voltage E1, all the counters 5-1 to 5-n are enabled. An output Q is generated from the counter t-1 at a shortest accumulation time t (=2·T). An alarm unit, a security unit, or the like (not shown) is driven in response to this detection signal. 
     As is apparent from the above description, when the smoke concentration is high, the smoke detection signal is immediately detected over a short accumulation time. However, when the smoke concentration is low, the smoke detection signal is slowly detected over a long period of time. The comparison voltages E1 to En and the counts of the counters 5-1 to 5-n are properly determined in association with the smoke concentration so as to obtain an inverse proportionality between the smoke concentration and the accumulation time, thereby obtaining highly reliable detection. 
     Referring to FIG. 1, the light-emitting element 8, the light-receiving element 9, and the amplifier 2 constitute a detector for converting smoke concentration analog information to an analog voltage signal. The oscillator 1 and the 2-input NAND gates 4-1 to 4-n constitute a sampling circuit for extracting an analog signal at every sampling period. The plurality of comparators 3-1 to 3-n constitute a quantizer, and the plurality of counters 5-1 to 5-n constitute an accumulating means. 
     FIG. 2 is a graph showing the relationship between the accumulation time and the smoke concentration of the detecting apparatus of the present invention, indicated by a solid line b, in comparison with that of a conventional apparatus, indicated by a dotted line a. In the conventional apparatus, even if a smoke concentration is high, a long accumulation time is required. However, according to the present invention, when the smoke concentration is increased, the accumulation time becomes short (the accumulation time may become zero as needed) in accordance with the degree of abnormality. 
     In the embodiment shown in FIG. 1, a single detecting apparatus is illustrated. However, when a plurality of detection signals from a fire alarm system which covers a wide monitor area are monitored at a concentrated central station, the analog signals from the detectors are monitored by the central station in accordance with polling or the like. In this case, when signal processing is performed by a microcomputer arranged in the central station, a very simple circuit configuration can be obtained without arranging a complicated circuit in each of the detecting apparatuses, resulting in low cost. 
     Signal processing for smoke detection by a computer in accordance with a program will be described with reference to a flow chart in FIG. 3. Assume that comparison voltages E1&#39;, E2&#39;, and E3&#39; satisfy the inequality E1&#39;&lt;E2&#39;&lt;E3&#39;, and that counts n1, n2, and n3 satisfy the inequality n1&gt;n2&gt;n3. In step S1, the microcomputer reads a detection voltage e0 using an analog to digital converting means which functions as a quantizer as an analog signal from a given detector, and the flow advances to step S2. In step S2, the microcomputer compares the detection voltage e0 with the comparison voltage E1&#39; and checks whether or not inequality e0≧E1&#39; is established. If YES in step S2, the flow advances to step S3. However, if NO in step S2, the flow advances to step S12. In step S12, a counter CNT1 is reset to zero. Thereafter, the flow advances to step S13. In step S3, the microprocessor causes the counter CNT1 to increment by one, and the flow advances to step S4. The microprocessor checks in step S4 whether or not the count of the counter CNT1 is n1. If YES in step S4, the flow advances to step S11. However, if NO in step S4, the flow advances to step S5. In step S5, the microprocessor compares the detection voltage e0 with the comparison voltage E2&#39; and checks whether or not inequality e0≧e2&#39; is established. If YES in step S5, the flow advances to step S13. The counter CNT2 is reset to zero in step S13, and the flow advances to step S14. However, as described above, if YES in step S5, the count of the counter CNT2 is incremented by one in step S6, and the flow advances to step S7. The microprocessor checks in step S7 whether or not the count of the counter CNT2 is n2. If YES in step S7, the flow advances to step S11. However, if NO in step S7, the flow advances to step S8. In step S8, the microprocessor compares the detection voltage e0 with the comparison voltage E3&#39; and checks whether or not the inequality e0≧e3&#39; is established. If YES in step S8, the flow advances to step S9. However, if NO in step S8, the flow advances to step S14. In step S14, a counter CNT3 is reset to zero, and the flow advances to step S15. However, when step S9 is executed, the count of the counter CNT3 is incremented by one, and the flow advances to step S10. The microprocessor checks in step S10 whether or not the count of the counter CNT3 is n3. If YES in step S10, the flow advances to step S11. However, if NO in step S10, the flow advances to step S15. Step S11 is the step for generating an abnormality detection signal when the step S4, S7, or S10 is judged to be YES. When step S11 is completed, the flow advances to step S15. Step S15 represents a node for another program. When a predetermined period of time has elapsed, the flow returns to step 1 for reading a detection voltage e0 from another or the same detector. When the read period for reading the detection voltage e0 from the same detector is T0, accumulation times of the counters CNT1 to CNT3 are T0·n1, T0·n2, and T0·n3, respectively. The counters CNT1 to CNT3 are reset to zero in steps S12, S13, and S14, respectively. However, when the counts of the counters CNT1 to CNT3 are not zero, highly reliable detection operation is performed by subtractions, respectively. 
     The present invention is not limited to an optical smoke detecting apparatus but can be extended to a detection apparatus for detecting an analog signal of a temperature, a gas, or the like and detecting an abnormality in accordance with the magnitude of the analog signal. 
     As has been described above, in the detection function of the environmental abnormality detecting apparatus, an abnormality detection time varies in accordance with a degree of abnormality given by an analog signal representing a certain phenomenon, thereby greatly improving reliability and optimizing the detection time. 
     Although various minor changes and modifications might be proposed by those skilled in the art, it will be understood that we wish to include within the claims of the patent warranted hereon all such changes and modifications as reasonably come within our contribution to the art.