Patent Publication Number: US-11043109-B2

Title: Fire notification facility

Description:
TECHNICAL FIELD 
     The present invention relates to a fire notification facility in which fire detectors are connected to a loop transmission path from a receiver to monitor fire. 
     BACKGROUND ART 
     Conventionally, in a fire notification facility known as an R type, terminal devices such as fire detectors each including a transmission function are connected to a transmission path drawn out from a receiver. At the time of detecting a fire, for example, based on a fire interrupt from the fire detector, a search command is issued to identify the address of a fire detector which issues a notification and display the fire-occurring address. Also, fire data is collected from the identified fire detector for monitoring. 
     In this manner, if the address of the fire detector which detects a fire is found, appropriate escape guiding and fire fighting can be performed. This is an indispensable function for fire monitoring particularly in large-sized facilities. 
     Also, to ensure reliability with respect to a break fault in the transmission path drawn out from the fire receiver, a fire notification facility has been known in which fire detectors are connected to a loop transmission path connected in a loop shape to the receiver to monitor fire. 
       FIG. 10  is a descriptive diagram of a conventional fire notification facility using a loop transmission path, in which a normal monitoring state is depicted in  FIG. 10(A)  and a case in which a break fault occurs is depicted in  FIG. 10(B) . 
     As depicted in  FIG. 10(A) , a transmission path  12  using paired signal lines are drawn out from a transmitting unit  23  provided to a receiver  10 . The transmission path  12  is arranged in a loop shape of being drawn out from the receiver  10  and then returning to the receiver  10  again. In the following description, the transmission path  12  connected in a loop shape to the receiver  10  is referred to as a loop transmission path  12 . 
     Between the signal lines of the loop transmission path  12 , fire detectors  18  each including a transmitting function are attachably and detachably connected via detector bases  16 . To each fire detector  18 , a unique detector address is set. With a downstream signal for changing a line voltage being transmitted from a transmitting unit  23  and an upstream signal for changing a line current being transmitted from any fire detector  18 , fire is monitored. 
     At the termination of the loop transmission path  12  drawn into the receiver  10 , a break monitoring control unit  28  is provided, monitoring a break fault in the loop transmission path  12  based on the line voltage supplied from the transmitting unit  23  to the loop transmission path  12 . Also, at the termination of the loop transmission path  12 , switching circuit units  30   a  and  30   b  are provided which perform switching connection of the signal line at the termination to the transmitting unit  23 . In a normal monitoring state, the switching circuit units  30   a  and  30   b  render the transmitting unit  23  as being in an insolation state. 
     As depicted in  FIG. 10(B) , during operation, if a break  31  occurs in the course of the loop transmission path  12 , the break monitoring control unit  28  detects a break fault because the line voltage at the termination of the loop transmission path  12  is interrupted to activate the switching circuit units  30   a  and  30   b , and connects a termination side of the loop transmission path  12  to the transmitting unit  23 . 
     Thus, a signal from the transmitting unit  23  is transmitted via the switching circuit units  30   a  and  30   b  from the termination side of the loop transmission path  12  toward the location of occurrence of the break  31 , allowing signal transmission and reception to and from the fire detector  18  connected between the location of occurrence of the break  31  and the termination of the loop transmission path  12 . If a break fault occurs, the fire monitoring function by the fire detectors  18  connected to the loop transmission path  12  is not lost, and high reliability can be acquired. 
     RELATED ART DOCUMENTS 
     
         
         Patent Document 1: Japanese Patent Application Publication No. 2008-004033; and 
         Patent Document 2: Japanese Patent Application Publication No. 2010-114632. 
       
    
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     However, in the conventional fire notification facility as described above, as depicted in  FIG. 10(B) , when the break  31  occurs in the course of the loop transmission path  12 , the break monitoring control unit  28  detects a break fault and causes the switching circuit units  30   a  and  30   b  to connect the termination side of the loop transmission path  12  to the transmitting unit  23  for signal transmission from both sides of the break location to the loop transmission path  12 . Thus, the fire monitoring function by the fire detectors  18  connected to the loop transmission path  12  is not lost. However, there is a problem in which the receiver  10  cannot detect where the break occurs in the loop transmission path  12  and it takes time and effort until the break location is found for recovery. 
     An object of the present invention is to provide a fire notification facility which allows a break section to be easily found on a receiver side when a break occurs in a loop transmission path and signal transmission is allowed from both sides of the location of the break to continue fire monitoring. 
     Means for Solving the Problems 
     (Fire Notification Facility) 
     The present invention is characterized in that, in a fire notification facility in which: a fire detector is connected to a loop transmission path connected in a loop shape to a receiver or a relay connected to the receiver; when the loop transmission path is normal, a signal is transmitted from a transmitting unit of the receiver or relay connected to a starting end of the loop transmission path to the fire detector to monitor fire; and when a break occurs in the loop transmission path, a termination of the loop transmission path is connected to the transmitting unit to transmit a signal from both ends of the loop transmission path to the fire detector to monitor fire, 
     a current direction detecting unit is provided which is connected to the loop transmission path, has a unique address set thereto, detects a current direction flowing through the loop transmission path in a predetermined direction as a current normal direction and detects a current flowing through a direction opposite to the current normal direction as a current reverse direction. 
     (Detection of Current Direction by Current Detection Resistor) 
     The current direction detecting unit detects a current detection voltage by a current flowing through a current detection resistor connected in series to the loop transmission path, 
     detects the current normal direction when the current detection voltage is a plus voltage or zero volt when a power supply voltage is supplied to the current direction detecting unit from an upstream side of the current detection resistor, and 
     detects the current reverse direction when the current detection voltage is a minus voltage or zero volt when a power supply voltage is supplied to the current direction detecting unit from a downstream side of the current detection resistor. 
     (Relay Provided with Current Direction Detecting Unit) 
     A plurality of said current direction detecting units are provided to relays connected to the loop transmission path among the plurality of fire detectors connected to the loop transmission path. 
     (Detector Base Provided with Current Direction Detecting Unit) 
     The plurality of current direction detecting units are provided to detector bases which each attach ably and detachably connect the fire detector to the loop transmission path. 
     (Detector Provided with Current Direction Detecting Unit) 
     The current direction detecting unit is provided to the fire detector connected to the loop transmission path. 
     (Current Direction Detecting Unit Provided with Display Unit) 
     The current direction detecting unit includes a display unit which displays a current direction. 
     (Break Section Determining Unit) 
     A plurality of said current direction detecting units are provided to the loop transmission path to transmit the current direction to the receiver or the relay, and furthermore, a break section determining unit is provided to the receiver or the relay, the break section determining unit determines, as a break section, a section in which the current normal direction detected at the plurality of current direction detecting units is changed to the current reverse direction when a break occurs in the loop transmission path, and notifies as such. 
     (Color-Coding Display of Break Section) 
     The fire receiver causes a screen display of a disaster-prevention facility map where address arrangement of the loop transmission path and the plurality of current direction detecting units is displayed, and 
     the break section determining unit causes a current normal group including one or a plurality of said current direction detecting units in which the current normal direction is detected and a current reverse group including one or a plurality of said current direction detecting units in which the current reverse direction is detected to be displayed by color coding with different predetermined colors, and causes occurrence of a break between the color-coded current normal group and current reverse group to be displayed. 
     (At-A-Glance Display of Detected Direction of Current Direction Detecting Unit) 
     The fire receiver makes an at-a-glance display with information for identifying the current direction detecting units and the current direction detected by the current direction detecting units associated with each other. 
     Effects of the Invention 
     (Basic Effects) 
     In the present invention, in a fire notification facility in which: a fire detector is connected to a loop transmission path connected in a loop shape to a receiver or a relay connected to the receiver; when the loop transmission path is normal, a signal is transmitted from a transmitting unit of the receiver or relay connected to a starting end of the loop transmission path to the fire detector to monitor fire; and when a break occurs in the loop transmission path, a termination of the loop transmission path is connected to the transmitting unit to transmit a signal from both ends of the loop transmission path to the fire detector to monitor fire, a current direction detecting unit is provided which is connected to the loop transmission path, has a unique address set thereto, detects a current direction flowing through the loop transmission path in a predetermined direction as a current normal direction and detects a current flowing through a direction opposite to the current normal direction as a current reverse direction. Thus, the break section of the loop transmission path can be easily found, and repairment and replacement is quickly performed on the break location of the loop transmission path to allow the loop transmission path to be recovered to become in a normal state, thereby allowing facility reliability to be ensured. 
     (Effects of Detection of Current Direction by Current Detection Resistor) 
     Also, the current direction detecting unit detects a current detection voltage by a current flowing through a current detection resistor connected in series to the loop transmission path, detects the current normal direction when the current detection voltage is a plus voltage or zero volt when a power supply voltage is supplied to the current direction detecting unit from an upstream side of the current detection resistor, and 
     detects the current reverse direction when the current detection voltage is a minus voltage or zero volt when a power supply voltage is supplied to the current direction detecting unit from a downstream side of the current detection resistor. Thus, when a break occurs in the loop transmission path on a downstream side or upstream side of any relay and a normal current or reverse current does not flow through the current detection resistor because a fire detector is not connected between the relay and the break location and the current direction detecting unit detects a current detection voltage of 0 volt, the current normal direction or the current reverse direction is detected, thereby making it possible to determine on which of the upstream side and the downstream side of the relay the break location occurs when the break detection voltage of 0 volt is detected. 
     (Effects by Relay Provided with Current Direction Detecting Unit) 
     Furthermore, the current direction detecting unit is provided to a relay connected to the loop transmission path among the plurality of fire detectors connected to the loop transmission path. 
     Thus, by detection of the current direction at the relay, a section of the relay in which the current normal direction is changed to the current reverse direction can be determined as a break section and a notification as such can be made. 
     (Effects by Detector Base Provided with Current Direction Detecting Unit) 
     Still further, the current direction detecting unit is provided to a detector base which attachably and detachably connects the fire detector to the loop transmission path. Thus, by detection of the current direction at the detector base, a section of the detector base in which the current normal direction is changed to the current reverse direction can be determined as a break section and a notification as such can be made. 
     (Effects by Detector Provided with Current Direction Detecting Unit) 
     Yet still further, the current direction detecting unit is provided to the fire detector connected to the loop transmission path. Thus, by detection of the current direction at the detector, a detector section in which the current normal direction is changed to the current reverse direction can be determined as a break section and a notification as such can be made. 
     (Effects by Current Direction Detecting Unit Provided with Display Unit) 
     Yet still further, the current direction detecting unit includes a display unit which displays a current direction. Thus, when a break occurs, the operator advances in the wiring direction while checking the display unit of the terminal including the current direction detecting unit and can thereby grasp a section in which the current normal direction is changed to the current reverse direction as a break section. 
     (Effects of Break Section Determining Unit) 
     Yet still further, a plurality of said current direction detecting units are provided to the loop transmission path to transmit the current direction to the receiver or the relay, and furthermore, a break section determining unit is provided to the receiver or the relay, the break section determining unit determines, as a break section, a section in which the current normal direction detected at the plurality of current direction detecting units is changed to the current reverse direction when a break occurs in the loop transmission path, and notifies as such. Thus, the break section of the loop transmission path can be easily found on a receiver side, and repairment and replacement is quickly performed on the break location of the loop transmission path to allow the loop transmission path to be recovered to become in a normal state, thereby allowing facility reliability to be ensured. 
     (Effects by Color Coding Display of Break Section) 
     The fire receiver causes a screen display of a disaster-prevention facility map where arrangement of the loop transmission path and the plurality of current direction detecting units are displayed, and the break section determining unit causes a current normal group including one or a plurality of said current direction detecting units in which the current normal direction is detected and a current reverse group including one or a plurality of said current direction detecting units in which the current reverse direction is detected to be displayed by color coding with different predetermined colors, and causes occurrence of a break between the current normal group and the current reverse group color-coded. Thus, when a break occurs in the loop transmission path, for example, a disaster-prevention facility map with the loop transmission path, the fire detector, and the current direction detecting units indicated thereon is displayed on a display of the receiver. 
     A current normal group including one or a plurality of current direction detecting units in which the current normal direction is detected in the disaster-prevention facility map is di splayed with, for example, green. On the other hand, a current reverse group including one or a plurality of current direction detecting units in which the current reverse direction is detected is displayed with, for example, red, and it is possible to display that a break occurs between the green current normal group and the red current reverse group. 
     (Effects by At-A-Glance Display of Detected Direction of Current Direction Detecting Unit) 
     The fire receiver makes an at-a-glance display with information for identifying the current direction detecting units and the current direction detected by the current direction detecting units associated with each other. Thus, when a break occurs in the loop transmission path, for example, the name, address, and current direction of a terminal including the current direction detecting unit are displayed on a display of the receiver, thereby allowing terminals in the current normal direction and terminals in the current reverse direction to be found at a glance and helping identifying the break location. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a descriptive diagram depicting a general outline of a fire notification facility with relays each including a current direction detecting function provided on a loop transmission path. 
         FIG. 2  is a block diagram depicting an embodiment of each relay including the current direction detecting function of  FIG. 1 . 
         FIG. 3  is a block diagram depicting another embodiment of the relay including the current direction detecting function of  FIG. 1 . 
         FIG. 4  is a descriptive diagram depicting a current direction flowing through the relays by transmission of an upstream signal from a fire detector when a break fault occurs in the loop transmission path. 
         FIG. 5  is a descriptive diagram depicting one example of a disaster-prevention facility map displayed on a receiver. 
         FIG. 6  is a descriptive diagram depicting one example of a break section display by the disaster-prevention facility map. 
         FIG. 7  is a descriptive diagram depicting a general outline of a fire notification facility with a current direction detecting function provided on a detector base. 
         FIG. 8  is a block diagram depicting an embodiment of the detector base including the current direction detecting function of  FIG. 7 . 
         FIG. 9  is a block diagram depicting an embodiment of a fire detector including a current direction detecting function. 
         FIG. 10  is a descriptive diagram depicting a conventional fire notification facility with a loop transmission path provided thereto. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     [Fire Notification Facility] 
     (General Outline of Fire Notification Facility) 
       FIG. 1  is a descriptive diagram depicting a general outline of a fire notification facility with relays each including a current direction detecting function provided on a loop transmission path. As depicted in  FIG. 1 , in an administrator room on the first floor of a building with a fire notification facility installed therein or the like, for example, an R-type receiver  10  is installed. 
     From the receiver  10  to a warning zone, a loop transmission path  12  is drawn using paired signal lines  14   a  and  14   b.    
     To the loop transmission path  12 , a plurality of fire detectors  18  each having a transmission function with a unique address set thereto are attachably and detachably connected via a detector base  16 . Also, to a loop transmission path  12  between the fire detectors  18 , a relay  20  is connected, which includes a current direction detecting function and has a transmission function with a unique address set thereto. 
     The current direction detecting function provided to the relay  20  detects, as a current normal direction, a current direction of a current i indicated by an arrow flowing by transmission of the upstream signal from the fire detector  18  to the loop transmission path  12  in a normal state without a break fault, and also detects a current −i flowing in a direction opposite to the current normal direction as a current reverse direction for transmission to the receiver  10 . 
     Here, the maximum number of addresses set to terminals including the fire detectors  18  and the relays  20  connected to the loop transmission path  12  is assumed as, for example, 255. To the loop transmission path  12 , 254 terminals at maximum including fire detectors  18  and the relays  20  can be connected. 
     Also in  FIG. 1 , for ease of description, it is assumed that six fire detectors  18  and five relays  20  are connected, the addresses of the fire detectors  18  are A 1 , A 2  . . . A 6  from a starting end side of the loop transmission path  12 , and the addresses of the relays  20  are A 7 , A 8 , . . . A 11  from a starting end side. 
     (Functional Structure of Receiver) 
     The receiver  10  includes a reception control unit  22 , a transmitting unit  23 , an operating unit  24 , a display unit  25  including a liquid-crystal display and a display light, an alert unit  26 , a transfer unit  27 , a break monitoring control unit  28 , and switching circuit units  30   a  and  30   b.    
     The reception control unit  22  is assumed to be a computer circuit or the like including a CPU, a memory, various input/output ports, and so forth. The transmitting unit  23  transmits and receives signals by following a predetermined communication protocol between the fire detectors  18  and the relays  20  connected to the loop transmission path  12 . 
     A downstream signal from the transmitting unit  23  to any fire detector  18  is transmitted in voltage mode. This signal in voltage mode is transmitted as a voltage pulse which changes a line voltage of the loop transmission path  12  between, for example, 18 volts and 30 volts. 
     By contrast, an upstream signal from any of the fire detectors  18  and the relays  20  to the receiver  10  is transmitted in current mode. In this current mode, a signal current is let flow to the loop transmission path  12  at a timing of bit  1  of transmission data, and the upstream signal is transmitted to the receiver as a so-called current pulse string. Thus, when the fire detector  18  transmits an upstream signal to the receiver  10 , the current i flows by a route of (receiver  10  plus side)→(signal line  14   a )→(fire detector  18 )→(signal line  14   b )→(receiver  10  minus side), and a current normal direction is detected at the relay  20  positioned therebetween. 
     Fire monitoring control by the reception control unit  22  of the receiver  10  is as follows. 
     During normal monitoring, the reception control unit  22  instructs the transmitting unit  23  at every constant cycle to transmit broadcast collective AD conversion signals including collective AD conversion commands. The fire detector  18  receiving this collective AD conversion signal detects and retains smoke concentration or temperature as sensor data. Subsequently, the reception control unit  22  transmits call signals including polling commands which sequentially specify terminal addresses. 
     Upon receiving a call signal with an address matching its self address, the fire detector  18  transmits to the receiver  10  a response signal including sensor data retained at that time. Upon detecting fire, the fire detector  18  transmits to the receiver  10  a fire interrupt signal. Upon receiving the fire interrupt signal via the transmitting unit  23 , the reception control unit transmits a group search command signal to identify a group including the fire detector  18  which detects fire and, subsequently, transmits an in-group search command signal to identify the address of the fire detector  18  which detects fire and display the fire-occurring address and collect fire data from the identified fire detector for monitoring. 
     This point similarly applies to the relays  20 . The relay  20  receiving the collective AD conversion signal from the receiver  10  detects and retains a current normal direction or current reverse direction based on the current direction detected at that time and, subsequently, upon receiving the transmitted call signal including a polling command which specifies the self address, transmits to the receiver  10  a response signal including the current normal direction or current reverse direction retained at that time. 
     In this manner, with each fire detector  18  and the relay  20  receiving a call signal, with its self address specified, regularly transmitted from the receiver  10  and transmitting a response signal, upstream signal transmission is performed substantially continuously on the loop transmission path  12 . This causes the current i in the current normal direction, and the relays  20  always detects the current normal direction and transmits a response signal to the receiver  10 . 
     The break monitoring control unit  28  detects and monitors a signal voltage acquired at the termination of the loop transmission path  12 . 
     When a break occurs in the loop transmission path  12 , the signal voltage is broken and cannot be detected, and thus a break is detected. With ON activation of the switching circuit units  30   a  and  30   b  using relay contacts and switch elements, the transmitting unit  23  is connected to the termination of the loop transmission path  12 . With parallel signal transmission and reception being performed to and from a transmission path between both ends and the break position of the loop transmission path  12 , recovery from the break fault is performed. 
     In this manner, with ON activation of the switching circuit units  30   a  and  30   b  by the break monitoring control unit  28  to start performing parallel signal transmission and reception to and from the transmission path between both ends and the break position of the loop transmission path  12 , when the fire detectors  18  connected between the termination and the break position of the loop transmission path  12  each transmit an upstream signal to the receiver  10 , the current −i flows in a direction opposite to that before the break on a route (receiver  10  plus side)→(signal line  14   b )→(fire detector  18 )→(signal line  14   a )→(receiver  10  minus side). 
     At the relays  20  positioned therebetween, a current reverse direction is detected and is transmitted to the receiver  10 . 
     The reception control unit  22  is provided with a break section determining unit  32  as a function to be achieved with program execution by the CPU. When a break occurs in the loop transmission path  12 , the break section determining unit  32  performs control of determining a section where the current normal direction detected at the relays  20  changes to the current reverse direction as a break section and notifying as such. 
     Also, as a notification of a break section by the break section determining unit  32 , when a break fault is detected, control is performed such that a disaster-prevention facility map where the receiver  10 , the loop transmission path  12 , the fire detectors  18 , and the relays  20  are indicated is displayed on the liquid-crystal display provided to the display unit  25  and a current normal group including the relays  20  where the current normal direction is detected and a current reverse group including other relays  20  where the reverse current direction is detected are displayed and color-coded with different predetermined colors, causing the occurrence of a break between the color-coded current normal group and current reverse group to be displayed. 
     [Relay] 
       FIG. 2  is a block diagram depicting an embodiment of each relay including the current direction detecting function of  FIG. 1 . As depicted in  FIG. 2 , the relay  20  is configured of a control unit  34 , a transmitting unit  36 , a current direction detecting unit  38 , a current detection resistor  40 , an isolation circuit unit  42 , and switch circuit units  44   a  and  44   b , and operates as receiving power supply from signal lines  14   a  and  14   b  or power supply from a dedicated power supply line. 
     The current direction detecting unit  38  detects a voltage occurring across both ends by a current flowing through the current detection resistor  40  with a small resistance value inserted and connected to the signal line  14   a . At normal time without a break on the loop transmission path  12 , the normal current i indicated by a solid line flows. When a downstream signal transmitted from the termination side of the loop transmission path  12  due to a break is received, the reverse current −i indicated by a dotted line flows. Note that while the normal current i or the reverse current −i at the current detection resistor  40  flows by transmission of the upstream signal by any fire detector  18 , either the normal current i or the reverse current −i supplied to the transmitting unit  36  and so forth further flows by transmission of the upstream signal by the transmitting unit  36  of any relay  20 . 
     Since the polarity of the current detection voltage occurring across both ends of the current detection resistor  40  is reversed between the case where the normal current i flows and the case where the reverse current −i flows through the current detection resistor  40 , the current direction detecting unit  38  detects a current normal direction when a current detection voltage with a polarity by the normal current i is acquired, and detects a current reverse direction when a current detection voltage with a reverse polarity by the reverse current −i is acquired. 
     Here, the relay  20  of  FIG. 2  is configured to supply a power supply voltage Vcc to circuit blocks such as the control unit  34  and the transmitting unit  36  to the current direction detecting unit  38  from an upstream side of the current normal direction. When the loop transmission path  12  is broken on a downstream side of the relay  20  and no fire detector  18  is connected between the relay  20  and the break location, the normal current i does not flow through the current detection resistor  40 , and the current detection voltage is 0 volt. Also in this case, the current direction detecting unit  38  detects a current detection voltage of 0 volt as being in a current normal direction. 
     By contrast, as depicted in  FIG. 3 , the configuration may be such that the power supply voltage Vcc is supplied to the circuit blocks such as the control unit  34  and the transmitting unit  36  to the current direction detecting unit  38  from a downstream side of the current normal direction. 
     However, when the loop transmission path  12  is broken on an upstream side of the relay  20  and no fire detector  18  is connected between the relay  20  and the break location, the reverse current −i does not flow through the current detection resistor  40 , and the current detection voltage is 0 volt. 
     Also in this case, the current direction detecting unit  38  detects a current detection voltage of 0 volt as being in a current reverse direction. 
     Note that the relay  20  of  FIG. 3  is the same as the relay  20  of  FIG. 2  except that it connects the transmitting unit  36  to the loop transmission path  12  on a downstream side of the current detection resistor  40  to take out the power supply voltage Vcc. 
     In this manner, when the control unit  34  and others are away from the current direction detecting unit  38  with respect to a break direction and no terminal is arranged between the break location and the relay, the current direction detecting unit  38  detects 0 volt. However, with the structure as described above, it can be determined on which of the upstream side and the downstream side of the relay  20  the break location occurs when the break detection voltage of 0 volt is detected. 
     The transmitting unit  36  receives a downstream signal transmitted in voltage mode due to a change in line voltage from the receiver  10 , and transmits to the receiver  10  an upstream signal in current mode due to a change in line current. 
     The control unit  34  performs control of, when receiving a collective AD conversion signal from the receiver  10  via the transmitting unit  36 , retaining the current normal direction or the current reverse direction detected at the current direction detecting unit  38  at that time and, subsequently, when receiving a call signal including a polling command with its self address specified, transmitting a response signal including the current normal direction or the current reverse direction retained at that time to the receiver  10 . An interrupt signal may be sent to the receiver  10  at the time of current direction reversal, and the receiver may sequentially perform polling on addresses from which an interrupt signal is received to communicate with a relay in a reverse direction. 
     Also, when determining an overcurrent due to a short-circuit fault in the loop transmission path  12  from the detection voltage of the current direction detecting unit  38 , the control unit  34  performs control, as a short-circuit isolator, of instructing the isolation circuit unit  42  to turn off the switch circuit units  44   a  and  44   b  and the switch circuit units  45   a  and  45   b , which are ON in a normal state, isolate the loop transmission path  12  where the short-circuit fault occurs. 
     Note that the relay  20  of the present embodiment is only required to achieve at least the current direction detecting function and, for this, includes the control unit  34 , the transmitting unit  36 , the current direction detecting unit  38 , and the current detection resistor  40  and is not necessarily required to be provided with a short-circuit isolator by the isolation circuit unit  42  and the switch circuit units  44   a  and  44   b.    
     Furthermore, it is desirable to provide the relay  20  with a display unit such as an LED display which displays the current direction detected by the current direction detecting unit  38 . When a display unit indicating a current direction is provided to the relay  20 , at the time of occurrence of a break, an operator can grasp a section in which the current normal direction is changed to the current reverse direction as a break section by advancing in a wiring direction while checking the display unit of the relay  20 . 
     [Operation when Loop Line Breaks] 
       FIG. 4  is a descriptive diagram depicting a current direction flowing through the relays by transmission of an upstream signal from the fire detector when a break fault occurs in the loop transmission path. 
     As depicted in  FIG. 4 , if it is assumed that a break  31  occurs in the loop transmission path  12  between the fire detector  18  at the address A 3  and the fire detector  18  at the address A 4 , the break monitoring control unit  28  of the receiver  10  detects that a line voltage at the termination of the loop transmission path  12  is broken by the break  31  and turns the switching circuit units  30   a  and  30   b  ON, and connects the transmitting unit  23  to the termination of the loop transmission path  12 . Thus, with respect to the location of occurrence of the break  31 , the state becomes such that downstream signals outputted from the transmitting unit  23  are transmitted from both sides, the starting end and the termination, of the loop transmission path  12 . 
     With this, like before the break, the fire detectors  18  at the addresses A 1  to A 3  and the relays  20  at the addresses A 7  to A 9  connected between the starting end of the receiver  10  and the location of occurrence of the break  31  each receive a downstream signal from the starting end side of the loop transmission path  12  and transmit an upstream signal to the starting end side of the loop transmission path  12 , and the relays  20  at the addresses A 7  and A 8  each detect a current normal direction based on the normal current i indicated by a solid arrow for transmission to the receiver  10 . 
     Here, no current by transmission of the upstream signal from the fire detector  18  flows through the relay  20  at the address A 9 , and the current detection voltage is 0 volt. However, since this is detected as being in a current normal direction, three relays  20  at the addresses A 7  to A 9  detect a current normal direction for transmission to the receiver  10 . 
     By contrast, with the switching circuit units  30   a  and  30   b  turned ON by the break monitoring control unit  28 , the fire detectors  18  at the addresses A 4  to A 6  and the relays  20  at the addresses A 10  and A 11  connected between the termination of the loop transmission path  12  and the location of occurrence of the break  31  each receive, conversely to the case before the break, a downstream signal from the termination side of the loop transmission path  12  and transmit an upstream signal to the termination side of the loop transmission path  12 . 
     The relays  20  at the addresses A 10  and A 11  each detect, based on the reverse current −i indicated by a dotted arrow, a current reverse direction for transmission to the receiver  10 . 
     The break section determining unit  32  provided in the receiver  10  determines, as a break section, an address section in which a current direction corresponding to the address of the relay  20  is changed from the current normal direction to the current reverse direction. 
     Here, if it is assumed that the current normal direction is (+) and the current reverse direction is (−), 
     (A 7  A 8  A 9  A 10  A 11 )=(+ + + − −), 
     and the current normal direction is changed to the current reverse direction between the address A 9  and the address A 10 . Thus, it is possible to determine a section between the relay  20  at the address A 9  and the relay  20  at the address A 10  as a break section of the loop transmission path  12  and make a notification as such. 
     [Display of Break Section] 
       FIG. 5  is a descriptive diagram depicting one example of a disaster-prevention facility map displayed on the receiver. As depicted in  FIG. 5 , on a disaster-prevention facility map screen  48  displayed on the liquid-crystal display provided to the display unit  25  of the receiver  10  depicted in  FIG. 1 , for example, a map on the third floor in an A unit is displayed. The loop transmission path  12  indicated by a dotted line is drawn out from the receiver  10  to the inside of the facility. 
     To the loop transmission path  12 , fire detectors indicated by square marks and relays indicated by triangular marks are connected. To the fire detectors, addresses A 1  to A 13  are set from the starting end toward the termination. To the relays, addresses A 14  to A 25  are set from the starting end toward the termination. Also, at the fire detectors and the relays, oval markers indicating addresses are displayed. 
       FIG. 6  is a descriptive diagram depicting one example of a break section display by the disaster-prevention facility map, depicting a display when a break  50  occurs in the loop transmission path  12  between the relay at the address A 14  and the relay at the address A 15 . 
     When the break  50  occurs, it is determined at the break section determining unit  32  that the relay at the address A 13  positioned between the starting end side of the loop transmission path  12  and the location of occurrence of the break  50  belongs to the current normal group and the relays at the addresses A 14  to A 25  positioned between the termination side of the loop transmission path  12  and the location of occurrence of the break  50  belong to the current reverse group. 
     Thus, the break section determining unit  32  determines a section between the relay at the address A 14  and the relay at the address A 15  as a break section, causes the relay at the address A 14  belonging to the current normal group and the fire detector at the address A 1  to be displayed as being assigned with, for example, blue, causes the relays at the addresses A 15  to A 25  belonging to the current reverse group and the fire detectors at the addresses A 2  to A 13  to be displayed as being assigned with, for example, red, and causes a partition interposed between the blue current normal group and the red current reverse group as a break section by color coding. 
     Also, on an upper part of the screen, “BREAK FAULT OCCURRING, A 14 -A 15  SECTION” is displayed as a break fault display  48 . Furthermore, as for the break section of the loop transmission path  12 , a break mark as a cross mark indicating the break  50  is displayed. 
     With the display on the break section using the disaster-prevention facility map as described above, a disaster-prevention administrator or the like can easily and reliably know the position on the loop transmission path  12  in the facility where a break fault occurs and appropriately and quickly react, such as replacing and repairing the loop transmission path due to the break fault. 
     [Detector Base including Current Direction Detecting Function] 
       FIG. 7  is a descriptive diagram depicting a general outline of a fire notification facility with a current direction detecting function provided on a detector base, and  FIG. 8  is a block diagram depicting an embodiment of the detector base including the current direction detecting function of  FIG. 7 . 
     As depicted in  FIG. 7 , in the present embodiment, each detector base  16  which attachably and detachably connects the fire detector  18  to the loop transmission path  12  is provided with the function of the current direction detecting unit  38 , and the other structures and functions are the same as those of the embodiment of  FIG. 1 . 
     As depicted in  FIG. 8 , the detector base  16  has a cross-connection of the signal lines  14   a  and  14   b  of the loop transmission path  12 . To the signal lines  14   a  and  14   b , the fire detector  18  is attachably and detachably connected, electrically and mechanically, with fitting pieces of hardware  52   a  and  52   b.    
     The detector base  16  is provided with the control unit  34 , the transmitting unit  36 , the current direction detecting unit  38 , and the current detection resistor  40 , and operates as receiving power supply from the signal lines  14   a  and  14   b  or power supply from a dedicated power supply line. 
     Since the polarity of the current detection voltage occurring across both ends of the current detection resistor  40  is reversed between the case where the normal current i flows and the case where the reverse current −i flows through the current detection resistor  40 , the current direction detecting unit  38  detects a current normal direction when a current detection voltage with a polarity by the normal current i or a current detection voltage of 0 volt is acquired, and detects a current reverse direction when a current detection voltage with a reverse polarity by the reverse current −i is acquired. 
     The transmitting unit  36  receives a downstream signal transmitted due to a change in line voltage from the receiver  10 , and transmits an upstream signal to the receiver  10  due to a change in line current. 
     The control unit  34  performs control of, when receiving a collective AD conversion signal from the receiver  10  via the transmitting unit  36 , retaining the current normal direction or the current reverse direction detected at the current direction detecting unit  38  at that time and, subsequently, when receiving a call signal including a polling command with its self address specified, transmitting a response signal including the current normal direction or the current reverse direction retained at that time to the receiver  10 . 
     In this manner, by providing the detector base  16  with the control unit  34 , the transmitting unit  36 , the current direction detecting unit  38 , and the current detection resistor  40 , compared with the case as in  FIG. 1  in which the relay  20  is connected to the loop transmission path  12  between the fire detectors  18 , the facility structure is simplified. Similarly, for the occurrence of a break fault in the loop transmission path  12 , the receiver  10  can determine a break section and inform as such. 
     [Fire Detector including Current Direction Detecting Function] 
       FIG. 9  is a block diagram depicting an embodiment of a fire detector including a current direction detecting function. As depicted in  FIG. 9 , in the present embodiment, the fire detector  18  attachably and detachably provided to the loop transmission path  12  via the detector base  16  is provided with the control unit  34 , the transmitting unit  36 , the current direction detecting unit  38 , the current detection resistor  40 , and a sensor unit  60 , and operates as receiving power supply from the signal lines  14   a  and  14   b  or power supply from a dedicated power supply line. 
     The sensor unit  60  has, for example, a known scattered-light-type smoke detection structure, intermittently light-emission driving a light-emitting unit using an infrared LED with a predetermined period, amplifying a light-receiving signal of the scatted light received at a light-receiving unit such as a photodiode, and outputting a smoke-concentration detection signal. Note that the sensor unit  60  may be provided with a temperature detecting unit in place of a smoke-detecting unit. As a temperature detecting element, the temperature detecting unit uses, for example, a thermistor, and, in this case, outputs a temperature detection signal as a voltage signal corresponding to a change of a resistance value due to temperature. 
     The control unit  34  includes a fire detecting function and a current direction detecting function. The fire detecting function of the control unit  34  is the same as the operation described for the fire detector  18  of  FIG. 1 , receiving a collective AD conversion signal from the receiver, AD converting and retaining sensor data and, subsequently, in response to a call signal including a polling command with its self address specified from the receiver, transmitting a response signal including the sensor data. Also, when, for example, a smoke-concentration detection signal outputted from the sensor unit  60  exceeds a predetermined fire threshold concentration, a fire is determined, and a fire interrupt signal is transmitted to the loop transmission path  12 . 
     The current direction detecting unit  38  detects a current normal direction when a current detection voltage with a polarity by the normal current i or a current detection voltage of 0 volt is acquired at the current detection resistor  40 , and detects a current reverse direction when a current detection voltage with a reverse polarity by the reverse current −i is acquired. 
     The transmitting unit  36  receives a downstream signal transmitted due to a change in line voltage from the receiver  10 , and transmits an upstream signal to the receiver  10  due to a change in line current. 
     The control unit  34  performs control of, when receiving a collective AD conversion signal from the receiver  10  via the transmitting unit  36 , retaining the current normal direction or the current reverse direction detected at the current direction detecting unit  38  at that time and, subsequently, when receiving a call signal including a polling command with its self address specified, transmitting a response signal including the current normal direction or the current reverse direction retained at that time to the receiver  10 . 
     In this manner, by providing the fire detector  18  with the control unit  34 , the transmitting unit  36 , the current direction detecting unit  38 , and the current detection resistor  40 , the control unit and the transmitting unit already provided to the fire detector  18  can be used they are as the control unit  34  and the transmitting unit  36 . Compared with the case in which the current direction detecting unit is provided to the detector base  16 , the facility structure is further simplified. For the occurrence of a break fault in the loop transmission path  12 , the receiver  12  can determine a break section and inform as such. 
     [Modification Examples of Present Invention] 
     While the relay including the current direction detecting function is connected between the fire detectors in the above-described embodiments, they are not limited by this, and the relay may be connected among a plurality of fire detectors. 
     Also, while a loop wiring is drawn out from the receiver in the above-described embodiments, they can similarly apply to a loop wiring drawn out from a relay connected to the receiver. The relay in this case has a structure of the receiver  10  of  FIG. 1  with the operating unit  24 , the display unit  25 , the alert unit  26 , and the transfer unit  27  removed therefrom, and fire monitoring and control are basically the same as that of the receiver  10 . 
     Upon detecting a fire, the relay transmits fire detection information to the receiver  10  to cause a fire alert to be outputted, and performs necessary control upon receiving an instruction by operation of the receiver  10 . 
     Furthermore, while a break section is indicated by displaying the current normal group and the current reverse group by color coding on the disaster-prevention facility map when a break fault occurs in the loop transmission path in the above-described embodiments, the break section may be indicated by displaying the break section with a specific color different from display colors of other sections. 
     Still further, in addition to the receiver, display may be made at a distributed display terminal. 
     Yet still further, before causing a current to flow from a reverse direction, the receiver may acquire and store terminal information regarding the presence or absence of a response. 
     Yet still further, the fire receiver may make an at-a-glance display with information for identifying the current direction detecting units and the current direction detected by the current direction detecting units associated with each other. 
     While a break section display is suitable because a break location can be grasped at a glance, a correspondence between a wiring diagram and a map is required, and implementation may be difficult. 
     In the at-a-glance display, terminals in the current normal direction and terminals in the current reverse direction can be known at a glance while the correspondence between the wiring diagram and the map is not required, which can help identify the break location. 
     Yet still further, while the fire notification facility with the R-type fire detectors connected via the loop transmission path from the R-type receiver is taken as an example in the above-described embodiments, they can similarly apply to a fire notification facility in which addresses are set to a loop-type detector line drawn out from a P-type receiver and addressable fire detectors each including a transmitting function are connected. 
     Yet still further, the present invention includes appropriate modifications without impairing its objects and advantages and, furthermore, is not limited by numerical values indicated in the above-described embodiments. 
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
           10 : receiver 
           12 : loop transmission path 
           14   a ,  14   b : signal line 
           16 : detector base 
           18 : fire detector 
           20 : relay 
           22 : reception control unit 
           23 : transmitting unit 
           28 : break monitoring control unit 
           30   a ,  30   b : switching circuit unit 
           32 : break section determining unit 
           34 : control unit 
           38 : current direction detecting unit 
           40 : current detection resistor 
           42 : isolation circuit unit 
           44   a ,  44   b : switch circuit unit 
           46 : disaster-prevention facility map screen 
           48 : break fault display 
           50 : break section display