Atmospheric abnormality detection alarm system
BACKGROUND OF THE INVENTION 
     The present invention relates to an alarm system. More particularly, the present invention relates to an atmospheric abnormality detection alarm system wherein a plurality of sensor terminals are separately connected to a single transmission line and are cyclically accessed by a main unit (central receiver). An accessed sensor terminal converts an analog signal (indicating smoke concentration, temperature, gas concentration or the like) to a digital signal which is then transmitted to the main unit. The main unit processes the digital signal to detect any atmospheric abnormality (e.g., fire or gas leakage) at this sensor terminal or malfunctioning of the sensor itself, and then displays the detected contents and generates an audible alarm. 
     In the conventional system of this type, when an abnormality is detected at a sensor terminal, the main unit indicates this sensor terminal by its address and generates an audible alarm in accordance with the alarm content. For example, maintenance personnel are made aware of the occurrence of a fire and its location. However, in practice, when maintenance personnel reach the detected site, it is very difficult to confirm the exact location where fire has broken out. This may disable early fire fighting, resulting in a big disaster. 
     SUMMARY OF THE INVENTION 
     The present invention eliminates the conventional drawback described above, and has for its object to provide an atmospheric abnormality detection alarm system wherein occurrence of an abnormality is indicated at a sensor terminal installed at the location of the detected fire or in the vicinity thereof (entrance of a room), so that maintenance personnel or foremen can readily confirm the exact location where fire has broken out. 
     In order to achieve the above object of the present invention, there is provided an atmospheric abnormality detection alarm system comprising a main unit connected to a transmission line for cyclically generating an address signal and an abnormal state display command signal. A plurality of sensor terminals are separately connected to the transmission line. Each of the plurality of sensor terminals are arranged to convert an analog output signal corresponding to one of the parameters smoke concentration, temperature and gas concentration to digital data when each sensor terminal is accessed by the main unit in response to a corresponding address signal. The digital data is then transmitted as response data to the main unit. Each sensor terminal has a command discriminator for receiving and deciphering the abnormal state display command transmitted from the main unit through the transmission line and a display/alarm circuit for displaying information indicating an atmospheric abnormality in response to an output signal from said command discriminator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an atmospheric abnormality detection alarm system according to a preferred embodiment of the present invention; and 
     FIGS. 2A and 2B show a flow chart for the system of FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An atmospheric abnormality detection alarm system according to an embodiment of the present invention will be first described in detail with reference to FIG. 1. 
     A main unit (central receiver) R has a central processing unit (to be referred to as a CPU hereinafter) 1, a memory 2, a display 3, a console 4, a transmission circuit 5, and so on. A program stored in the memory 2 is executed by the CPU 1. The CPU 1 supplies address and command signals for a sensor terminal D to the transmission circuit 5. The transmission circuit 5 converts these signals to serial data in a transmission format suitable for a transmission line L. A transmission circuit 6 in the sensor terminal D converts the serial data to parallel data having predetermined levels. In each of the sensor terminals D, an address comparator 7 compares the address represented by the transmitted address signal with an address assigned thereto. When these addresses coincide, a command discriminator 8 deciphers the command data. When the command data indicates data transmission, the command discriminator 8 causes an A/D converter 9 to transmit digital data onto the transmission line L through the transmission circuit 6. However, when the command data indicates data display, the command discriminator 8 causes a display/alarm circuit 10 to perform display in a predetermined mode. The display modes include a fire display mode, a breakdown display mode and so on. The fire display mode may be accompanied by an audible alarm. The A/D converter 9 receives an analog output signal from a sensor 11 and converts it to corresponding digital data. This digital data is transmitted onto the transmission line L through the transmission circuit 6 in response to the output from the command discriminator 8. 
     The operation of the atmospheric abnormality detection alarm system of the embodiment described above will now be described. 
     In normal operation, the main unit R cyclically generates an address signal for each sensor terminal D and a data transmission command signal therefor. The response data from the sensor terminal D is generally processed in accordance with a program stored in the memory 2. For example, the response data from the sensor terminal D is compared with reference data. If the response data is greater than the reference data, the CPU 1 determines that a fire has broken out and causes the display 3 to display the terminal number of the corresponding sensor terminal D. At the same time, an audible fire alarm is generated, and the CPU 1 transmits a fire display command to the corresponding sensor terminal D. Upon reception of the fire display command, the corresponding command discriminator 8 deciphers the fire display command and causes the display/alarm circuit 10 to indicate the existence of the fire. When the CPU 1 completes the above operation, the CPU 1 cyclically accesses the remaining sensor terminals D. Maintenance personnel can identify the general location of the detected fire by means of the display 3, and go immediately to the location where the fire has supposedly broken out. They then look for the activated display/alarm circuit 10 to confirm the exact location where the fire has broken out, thereby performing proper and quick response. In this case, when an audible alarm is generated by the display/alarm circuit 10, maintenance personnel can readily find the exact location. The alarm display can be situated in front of the entrance of the room in which the corresponding sensor is installed, so that maintenance personnel can readily find the location of the display/alarm circuit 10. Furthermore, a fire display can also be accompanied by a sensor breakdown display. In this case, repair personnel can easily repair the broken sensor. 
     According to the atmospheric abnormality detection alarm system described above, the main unit can cyclically access the plurality of sensor terminals. When an atmospheric abnormality is detected by the main unit in accordance with the response data from a given sensor terminal, the main unit transmits a display command to the given sensor terminal. This sensor terminal causes the command discriminator to present the fire display at its display/alarm circuit 10. Therefore, maintenance personnel can easily and quickly find the exact location where fire has broken out immediately after they reach the general location of the detected fire. 
     The main unit in the preferred embodiment can be any one of a number of standard computers or personal computers presently on the market. The transmission circuit 6 is a standard prior art I/O device for serial-to-parallel data conversion. Similarly the address comparator 7, A/D converter 9, and sensor 11 are devices well known in this art. The display/alarm circuit 10 can, in the preferred embodiment constitute an alarm or flashing light activated by the command discriminator 8. The command discriminator 8 comprises the integrated circuit EWD 106 of Fuji Electronics Co., Ltd. 
     FIG. 2 illustrates a preferred embodiment of a flow chart for the system of FIG. 1. 
     As the system is supplied power, the CPU 1 on the main unit R executes a program. First of all, an initializer subroutine shown on the flow diagram is called. In the routine, some buffers are set to predetermined values and all I/O (input and output) interfaces for the transmission circuit 5 and a console 4 etc, are set to proper commands. Of course a display 3 and audio alarms are also reset. 
     A register buffer shown on the flow chart requests transmission of control data to a same sensor D which has been processed and determined to be in an abnormal condition. Therefore, if a sensor D detects a fire and the CPU recognizes the fire, the Reg buffer is set to a value other than zero, and the sensor D is again called by the main unit R to transmit control data for indicating an abnormal state at the sensor D. In this case, the transmission circuit 5 will be set for a control command with control data. If the Reg. buffer is zero, a CSA (current sensor address) buffer is counted up by one so that a new sensor which is assigned a next current sensor address (CSA) is called. Also a digitized analog data transmission command is provided to the transmission circuit 5. 
     Next, an address of a sensor to which it is intended to transmit, i.e. the address contained in the CSA buffer, is also provided to the transmission circuit 6. The CPU triggers the circuit 5 to transmit an address data and a command data to the sensor D via the transmission line L. 
     After that, the main unit R waits for an interruption from the transmission circuit 5. The interruption results from analog data being received from the sensor. When the transmission circuit 5 has received such analog data, the circuit 5 sends an interruption signal to the CPU 1. If the CPU 1 receives the signal, the CPU 1 picks up the analog data from the transmission circuit 5. 
     In general, the analog data has a parity bit. Therefore, the CPU 1 can check whether a communication between the main unit R and the sensor D has been successful. If the parity bit is not proper, the analog data probably is not correct. In this case, the main unit R must display the sensor address on a trouble indicator and trigger a trouble alarm. 
     If the data is correct, the CPU 1 examines an analog data collection command at this time. If an analog data collection command is not present, return to circle 1. If an analog data collection command is present, the received analog data is compared with a predetermined value, i.e. an alarm level. If the analog data is greater than the level, the main unit R displays an address of the sensor D or a number of a zone or group related to the sensor D, and triggers an alarm sounder. In order to communicate with the same sensor D by a control command, the Reg. buffer also must be set to a value other than zero and a control data buffer, which is not shown in the flow chart, is set to a proper control data to indicate a status of the sensor D. 
     Thereafter, the CPU 1 executes from 1 again. However, at this moment, the Reg. buffer is not zero so that the main unit R does not renew a content of the CSA buffer and sends a control command with control data to the transmission circuit 5 to communicate with the sensor D. 
     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.