Abstract:
An environmental abnormality detection apparatus has a detection portion for detecting a phenomenon such as a fire or gas leakage, and a signal processor such as a microcomputer or the like for determining whether an environmental abnormality has occurred in accordance with a detection signal from the detection portion and for generating an alarm signal when the abnormality occurs. A power source control circuit is provided to intermittently supply power to the signal processor and to stop power supply in accordance with an end of processing signal from the signal processor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to an environmental abnormality detection apparatus used in an alarm device for a fire, gas leakage, or the like. 
     A conventional fire detector using a microcomputer in a signal processor for improving reliability is disclosed in Japanese Patent Disclosure (Kokai) No. 60-164896. In addition, a fire alarm device constituted by a receiver and a plurality of fire detectors is designed to minimize a monitoring current of each fire detector so as to reduce entire power consumption. 
     When a microcomputer is used in an environmental abnormality detection apparatus such as a fire detector, a highly reliable device, suitable to a place where alarm errors are not so often generated, can be provided. However, a microcomputer requires large power consumption regardless of whether it executes processing or not. Even a microcomputer using a CMOS requires several mA which is several hundreds times that of a conventional fire detector. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide an environmental abnormality detection apparatus wherein monitoring current consumption is minimized. 
     It is another object of the present invention to provide an environmental abnormality detection apparatus wherein optimum conditions can be set and variations in detection are less. 
     In order to achieve the above objects, there is provided an environmental abnormality detection apparatus having a detection portion for detecting a phenomenon such as a fire or gas leakage, a signal processor constituted by a microcomputer or the like for determining whether an environmentaI abnormality has occurred in accordance with a detection signal from the detection portion and for generating an alarm signal when the abnormality occurs, and a power source control circuit to intermittently supply power to the signal processor and to stop power supply in accordance with an end of processing signal from the signal processor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an embodiment of an environmental abnormaIity detection apparatus of the present invention; 
     FIG. 2 is a timing chart for explaining an operation of the detector in FIG. 1; and 
     FIG. 3 is a flow chart of the detector in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An environmental abnormality detection apparatus of the present invention will now be described in detail with reference to the accompanying drawings. 
     FIG. 1 is a block diagram of an embodiment of the environmental abnormality detection apparatus of the present invention. The environmental abnormality detection apparatus shown in FIG. 1 is an ionization smoke detector, terminals 40 and 41 of which are connected to a pair of transmission lines extending from a central monitor device (not shown). This ionization smoke detector includes a detection portion consisting of an ion chamber 11 which is ionized by a radiation source, a field effect transistor 12 for converting an impedance of an intermediate electrode of the ion chamber 11, and a resistor 13 for extracting an output from the field effect transistor 12; a signal processor consisting of an amplifier 20, an A/D converter 21, an I/O port 22, a RAM (Random Access Memory) 30, a ROM (Read Only Memory) 23, and a CPU 24; a power control circuit consisting of a transistor 14, an inverter 15, a flip-flop 31, and an oscillator 32; and an SCR 16 for short-circuiting a pair of transmission lines with a low impedance upon operation. The oscillator 32, the flip-flop 31, the inverter 15, and the ROM 30 are always supplied with power through a stabilized power source circuit (not shown). 
     An operation of the ionization smoke detector having the above arrangement will be described below with reference to the timing chart shown in FIG. 2. The oscillator 32 always outputs a pulse signal a of a predetermined cycle as shown in FIG. 2. The pulse signal a is input to a set terminal S of the flip-flop 31. When the flip-flop 31 is set, it sets a Q output b at a high level. Therefore, an output from the inverter 15 goes to a low level to cause a predetermined current to flow to the base of the transistor 14 so as to turn it on. At this time, power is supplied to the signal processor 2 through the transistor 14. When the CPU 24 of the signal processor 2 is supplied with power, it begins to execute programs stored in the ROM 23 from the beginning. Additionally, a voltage proportional to the smoke concentration detected in the ion chamber 11 is supplied across both the ends of the resistor 13. The smoke detection operation in the ion chamber 11 is the same as that of a conventional ionization smoke detector, and a detailed description thereof is not necessary. This detection voltage is amplified to be a predetermined level by the amplifier 20, A/D-converted by the A/D converter 21, and supplied to the I/O buffer 22. The CPU 24 determines whether an abnormality (fire) has occurred in accordance with past data stored in the RAM 30 and currently fetched data (smoke concentration). If the CPU 24 determines that no abnormality has occurred, it generates an end of processing signal c at the reset terminal R ofthe flip-fIop 31 through the I/O buffer 22. When the flip-flop 31 is reset, it sets the Q output b at a low level. An output from the inverter 15 goes to a high level to turn off the transistor 14, so that the signal processor 2 is no longer supplied with power. A pulse is supplied from the oscillator 32 again after a predetermined time, and the signal processor 2 is supplied with power to execute a monitoring operation. Thus, the monitoring operation is executed every few seconds in a normal monitoring state. If the signal processor 2 determines that an environmental abnormality has occurred, an alarm signal d is supplied from the I/O buffer 22. The alarm signal d is supplied to the gate of the SCR 16 to trigger it. Terminals 40 and 41 are then connected with a low impedance, so that an operation state of the detector can be supplied as an output to the outside. 
     When the CPU determines whether an environmental abnormality has occurred, processing of higher complexity requires more information such as past data (history data) and a time interval. When history data must be maintained, the RAM 30 must be continuously supplied with power. However, when history data is unnecessary, the RAM 30 need only be applied with power when the CPU 24 operates. 
     A fire alarm device can generally monitor a fire if a monitoring operation is executed every few seconds. In addition, if signal processing is executed by a microcomputer, the processing time becomes very short although it differs case by case, and power supply is stopped at the same time the signal processing is completed, resulting in efficient saving of energy. 
     An example of a program of the signal processing will now be described below with reference to the flow chart shown in FIG. 3. In step 70, a power source is turned on. In step 71, the CPU determines whether the power on is an initial power on in accordance with the presence or absence of a password which is registered in the RAM. If YES in step 71, the flow advances to step 72, and if NO in step 71, the flow advances to step 74. In step 72, the buffer (and other components as may be needed) are driven to execute the initialization routine. At the same time, the password is registered. In step 73, a sensor (smoke detection) output value S is fetched and an initial value REF is stored in the buffer. Then, the flow advances to step 78. In step 74, the sensor output value S is fetched. In step 75, the CPU determines whether the sensor output value S is larger than a predetermined alarm value ARM as compared with the initial value REF. If YES in step 75, the flow advances to step 79, and if NO in step 75, the flow advances to step 76. In step 79, a pulse (alarm signal) is output to the SCR to trigger it. In step 76, the CPU determines whether a difference between the sensor output value S and the initial value REF falls within a predetermined range ST. If YES in step 76, the flow advances to step 77, and if NO in step 76, the flow advances to step 78. In step 77, the initial value REF is updated to be a new sensor output value S. In step 78, the end of processing signal for resetting the flip-flop is generated. In step 80, the signal processing is ended and the power source is turned off. As described above, according to this program, the initial value REF as a reference value is initialized during initial power on (e.g., installation of the detector), and is automatically corrected thereafter during the monitoring operation to compensate for variation over time. 
     As has been described above, since the environmental abnormality detection apparatus of the present invention uses a microcomputer for the signal processing for determining environmental abnormalities, optimum conditions can be set, and variations in individual sensors can be minimized. In addition, power is supplied to the signal processor only for the processing time, resulting in less power consumption.