JP4501786B2 - Fire alarm system - Google Patents

Description

  The present invention relates to a fire alarm system having a plurality of fire detectors for detecting a fire and a receiving device for performing wireless communication using a radio wave as a medium between the fire detectors.

  2. Description of the Related Art Conventionally, various fire alarm systems have been provided that include a plurality of fire detectors that detect a fire and a receiver that receives a fire detection signal transmitted from the fire detector that detects a fire in a wired manner. On the other hand, wireless communication between the fire detector and the receiving device should be performed due to the advantage that the wiring between the fire detector and the receiving device is not required when newly installed in an existing facility. A fire alarm system has been proposed (see Patent Document 1).

  On the other hand, in any of the wired or wireless communication systems, in order to confirm that a plurality of fire detectors are operating normally, a transmission request message is periodically sent from the receiving device to each fire detector. And a response message indicating the operating state of each fire detector is returned to the receiving device, and based on the response message, it is determined whether or not a failure such as a dead battery has occurred in the fire detector.

  Here, in order to improve the reliability of the fire alarm system, it is necessary to exchange the periodic transmission request message and the response message as described above as frequently as possible. For example, in the EN standard (European unified standard), a standard (EN54-25) that obligates the exchange of messages at a rate of once every 300 seconds is planned.

By the way, periodic message exchange is frequently performed as described above, and the more the number of fire detectors included in the system, the higher the probability that a collision will occur due to overlapping transmission timings of the fire detectors. Therefore, it is necessary to avoid such a collision. Therefore, in the thing of patent document 1, while the carrier used for radio | wireless communication is detected, the carrier sense system which transmits a radio signal when a carrier is not detected without transmitting a radio signal is detected. It has been adopted.
Japanese Patent No. 2840367

  However, in the carrier sense system, since a certain time is required for switching between transmission / reception of radio circuits, collision cannot be completely avoided. In addition, in a wireless fire alarm system, a frequency assigned to a radio station that does not require a license is generally used, but in some countries, a severe limitation is imposed on transmission time duty. For example, in the European Union, the transmission time duty must be less than 0.1% at the Alarm frequency used in the fire alarm system.

  On the other hand, as a collision avoidance method when each fire detector adopts a pure aloha method in which packets are transmitted at random, a response message having the same content is continuously transmitted a plurality of times (hereinafter referred to as “continuous transmission”). Although a method is conceivable, if the number of continuous transmissions is increased, the transmission time duty also increases, so that the above condition (less than 0.1%) cannot be satisfied.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a fire alarm system capable of reliably exchanging messages between a receiving device and a fire detector while satisfying predetermined conditions.

In order to achieve the above object, the invention of claim 1 includes a plurality of fire detectors for detecting a fire, and a receiver for performing wireless communication using radio waves as a medium between the fire detectors. The sensor detects a fire by detecting temperature changes and smoke generated by a fire, a wireless transmission / reception means for transmitting / receiving a radio signal to / from the receiver, and at least the detection means detects a fire. Control means for controlling the wireless transmission / reception means to transmit the fire detection information by a wireless signal when received, and the receiving device transmits / receives a wireless signal to / from the fire detector, and wireless transmission / reception means And control means for obtaining fire detection information from a radio signal received by the wireless transmission / reception means, and the control means of the receiving device sends a transmission request message for requesting a predetermined response to all the fire detectors. The wireless detector periodically transmits a wireless signal from the line transmitter / receiver, and the fire detector control unit receives a predetermined response message indicating the operation state of the device from the wireless transmitter / receiver when receiving the transmission request message. Reply with a radio signal, and the control means of the receiving device and the fire detector is one downstream time slot from the receiving device to the fire detector, and from the fire detector assigned to each fire detector to the receiving device. A fire alarm system for exchanging a transmission request message and a response message in a superframe in which a plurality of frames composed of a plurality of uplink time slots are collected, and the control means of the fire detector is received from the receiving device. until a notification is the continuous transmissions times, the response of the same content in uplink time slot assigned to its own vessels for each of a plurality of frames messages Is transmitted from the wireless transmission / reception means as a wireless signal, and the receiving device adds the total of wireless signals allowed for each fire detector within one superframe according to the number of fire detectors included in the system. It is characterized by comprising a notification means for obtaining the number of times of continuous transmission that satisfies the condition that the transmission time is less than or equal to a predetermined threshold value and notifying each fire detector by a radio signal.

  According to a second aspect of the present invention, in the first aspect of the invention, the receiving device includes signal strength detecting means for detecting the signal strength of the radio signal received by the wireless transmitting / receiving means, and the notification means of the receiving device is the signal strength detecting means. It is characterized in that the number of continuous transmissions of a fire detector having a relatively high detected signal strength is relatively reduced.

According to the first aspect of the present invention, the notification means of the receiving device is configured to provide a radio signal permitted to each fire detector within one superframe according to the number of fire detectors included in the system. Obtain the number of continuous transmissions that satisfy the condition that the total transmission time is less than or equal to the predetermined threshold value and notify each fire detector by radio signal until the fire detector control means reaches the notified number of continuous transmissions. Since the response message having the same content is transmitted as a radio signal from the radio transmission / reception means in the uplink time slot assigned to the own frame for each of a plurality of frames , the predetermined condition is satisfied between the receiving device and the fire detector. The message exchange can be performed reliably, and the notification means of the receiving device automatically determines the number of continuous transmissions for the system and notifies each fire detector, so that the construction work is facilitated.

  According to the second aspect of the present invention, it is possible to reduce the traffic in periodic message exchange by eliminating unnecessary continuous transmission.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a system configuration diagram of this embodiment, and a fire alarm system is configured by one receiving device 1 and a plurality of fire detectors 10. In the following, when the fire detectors 10 are shown individually, they are indicated as fire detectors 10 ₁ , 10 ₂ ,..., 10 _n, and when they are shown collectively, they are indicated as fire detectors 10.

  The fire detector 10 is installed on the ceiling of a facility, for example, and as shown in FIG. 3A, a detection unit 11 that detects a fire by detecting a temperature change and smoke generated by a fire. And a radio transmission / reception unit 12 for transmitting / receiving a radio signal using a radio wave as a medium to / from the receiving apparatus 1 by modulating / demodulating a data format to be described later to a carrier wave of a prescribed frequency, For transmitting and receiving wireless signals, a control unit 13 for transmitting information and response messages by wireless signals, a sensing unit 11 using a battery as a power source, a wireless transmission / reception unit 12, and a battery power unit 14 for creating an operating power source for the control unit 13 An antenna 15 and a switch 16 that opens and closes a power feeding path from the power supply unit 14 to the wireless transmission / reception unit 12 under the control of the control unit 13 are provided. The control unit 13 includes a microcomputer and a nonvolatile memory such as an EEPROM as main components, and executes various processes described later by executing a program stored in the nonvolatile memory. Each fire detector 10 is given a unique address at the time of manufacture or construction and is stored in the nonvolatile memory of the control unit 13.

  On the other hand, the receiving device 1 is installed in, for example, a management room of a facility. As shown in FIG. 3B, the receiving device 1 modifies and demodulates a data format, which will be described later, to a carrier wave of a prescribed frequency. A wireless transmission / reception unit 2 for transmitting / receiving a radio signal using radio waves as a medium, an operation switch 3a for performing various settings, and a display device (for example, a liquid crystal display) 3b for performing a fire alarm and various displays In addition, a display operation unit 3 including a speaker 3c that sounds an alarm sound, an alarm message, and the like, a control unit 4 that controls the wireless transmission / reception unit 2 and the display operation unit 3, a wireless transmission / reception unit 2, and a display operation unit 3 from a commercial power source. A power supply unit 5 that creates an operating power supply for the control unit 4 and an antenna 6 for transmitting and receiving radio signals are provided. The control unit 4 includes a microcomputer and a nonvolatile memory such as an EEPROM as main components, and executes various processes described later by executing a program stored in the nonvolatile memory. A unique address different from that of the fire detector 10 is also given to the receiving device 1 at the time of manufacture or construction, and is stored in the nonvolatile memory of the control unit 4.

  Here, a frequency that does not require a license is used for wireless communication between the receiving device 1 and the fire detector 10. For example, radio characteristics conforming to low power security and specific low power radio standards in Japan, FCC Regulations Part 15 SubpartC in the US, and Short Range Device standards in Europe must be satisfied.

  A data format of data exchanged between the receiving device 1 and the fire detector 10 is shown in FIG. This data format consists of a 32-bit preamble (bit synchronization pattern) PR in which 1 and 0 alternate, a 16-bit unique word (frame synchronization pattern) UW consisting of a prescribed bit string, and a 32-bit allocated to the fire alarm system. A unique ID (system ID) SysID, an 8-bit unique ID (sensor ID) NodeID assigned to each fire detector 10, a 16-bit message Msg, and a 16-bit error detection code CRC Is done. That is, the unique address of the fire detector 10 is the system ID + sensor ID, and the unique address of the receiving device 1 is the system ID.

  When the receiving device 1 transmits a message specifying a specific fire detector 10, the detector ID of the fire detector 10 is specified as the sensor ID of the data format, and all the fire detectors 10 are specified. When broadcasting a message, it is only necessary to specify “0 (zero)” for the sensor ID of the data format. Further, when the fire sensor 10 sends a reply to the receiving device 1, the sensor ID of its own device may be set to the sensor ID of the data format and transmitted.

  On the other hand, in the fire detector 10 and the receiving device 1 that have received the wireless signal, the wireless transmission / reception units 12 and 2 amplify the reception signal, demodulate the data format, and output to the control units 13 and 4. The control units 13 and 4 sample the data demodulated by the radio transmission / reception units 12 and 2 at a digital input port provided in the microcomputer, extract the bit timing during reception of the preamble PR, and then successively 16 bits. The unique word is detected by shifting the received bits for one minute at a time until it matches the specified unique word. Furthermore, the control units 13 and 4 collate the received system ID and sensor ID with the unique address stored in the nonvolatile memory, and accept the message Msg when they match and no bit error is detected. .

  In the present embodiment, wireless communication between the receiving device 1 and the plurality of fire detectors 10 is performed by a time division multiple access (TDMA) method. That is, as shown in FIG. 5, the time slot B in one downstream direction (receiver 1 → fire detector 10) and the time in a plurality (99 in the illustrated example) upstream (fire detector 10 → receiver 1). A plurality of (30 in the illustrated example) frames F1 to F30 including slots D1 to D99 are collected to form a super frame SF, and the upstream time slots D1 to D99 in the frames F1 to F30 are assigned to each fire detector 10. By assigning them individually, even when the interval between periodic message exchanges (exchange of reply request message and response message) is relatively short, for example, once every 300 seconds in the EN standard described above The collision between the radio signals transmitted from the fire detector 10 can be reliably avoided. The time slots B and Di (i = 1 to 99) in the down direction and the up direction have a period of 100 milliseconds, and the breakdown is 50 milliseconds in the above data format. The wireless transmission / reception unit of the receiver 1 and the fire detector 10 20 milliseconds are assigned to the time (startup time) until the transmission is possible at a stable carrier frequency after starting 2 and 12, and 15 milliseconds are assigned to the guard time. The guard time is a free time for absorbing a timing difference caused by an error between the operation clock frequencies of the fire detector 10 and the receiver 1 (the operation clock frequency of the microcomputer configuring the control units 13 and 4). Further, the allocation of the upstream time slots D1 to D99 to each fire detector 10 is set by, for example, a dip switch provided in the fire detector 10, or stored in advance in the nonvolatile memory of the control unit 13 in the manufacturing process. Alternatively, it may be performed by a method such as assigning to each fire detector 10 in order from the receiving device 1 using wireless communication at the time of installation and storing in the nonvolatile memory of the control unit 13.

  By the way, by adopting the TDMA system as described above, it is possible to prevent the response messages returned from the fire detector 10 from colliding with each other, but the response message from the fire detector 10 is received by the receiving device due to the influence of external noise, interference waves, or the like. 1 can not be received. Therefore, in the present embodiment, a response message having the same content is returned (continuously sent) to the fire detector 10 in the upstream time slot Di assigned to each of a plurality of consecutive frames Fk-1, Fk,. A response message returned from the sensor 10 can be reliably received by the receiving device 1. Here, the number of times that the fire detector 10 can be continuously transmitted per superframe SF while satisfying the above-described transmission time duty limit (less than 0.1%) (number of consecutive transmissions) is obtained as follows. .

First, x stand for the number of fire detector 10 included in the system, T _B the time width of downlink time slot B, and the time width of the uplink time slot Di and T _D time width T of a single frame F _F is _{T F = T B + x ×} T D becomes, if the limit value of the transmission time duty and z%, and the time width T _D of the time width T _SF and the uplink time slot of the limiting value z and superframes SF Therefore, the number of continuous transmissions Ry (= T _SF / 100 × z / T _D ) allowed for each super frame SF for one fire detector 10 is obtained. On the other hand, since the upward time slot Di is assigned to each fire detector 10 once for each single frame Fk (k = 1, 2,...), One unit per superframe SF. continuous transmissions allowed number of the fire detectors 10 is calculated by dividing the time width T _SF superframe SF in the time width T _F of the frame F, the maximum number of repetitions y of the frame F included in the super frame SF (= T _SF ÷ T _F ) or less. After all, the upper limit of the number of continuous transmissions allowed for one fire detector 10 is y if y ≦ Ry, and Ry if Ry <y. For example, if T _SF = 300 seconds, z = 0.1%, T _B = T _D = 100 milliseconds, Ry is 3 times, and if x = 99 units, T _F = 10 seconds and y = 30 times ( > Ry), the upper limit value of the number of continuous transmissions under this condition is 3 times (= Ry).

In addition, the process which calculates | requires the above-mentioned continuous transmission frequency (upper limit value), the construction contractor operates the operation switch 3a of the display operation part 3 at the time of construction, the number x of the fire detectors 10, the time width T _{SF of} the super frame _SF , This is executed by the control unit 4 of the receiving apparatus 1 by inputting a condition such as a transmission time duty limit value z%. Moreover, the control part 4 of the receiver 1 notifies each fire detector 10 of the reply request message which designated the continuous transmission frequency below the upper limit calculated | required by the said process with a radio signal. The control unit 13 of the fire detector 10 continues to reply the response message in the uplink time slot Di assigned for each of the plurality of frames Fk until the number of continuous transmissions notified from the receiving device 1 is reached.

  Next, the operation of this embodiment will be described. First, a reply request message is periodically transmitted from the receiving device 1 to all the fire detectors 10, and a response message returned from each fire detector 10 is received by the receiving device 1. The operation for confirming whether the device 10 is operating normally will be described with reference to the time chart of FIG. 1 and the flowchart of FIG. However, in each fire detector 10, it is assumed that the number of continuous transmissions is notified in advance from the receiving device 1 and is stored in a nonvolatile memory constituting the control unit 13.

  When the power is turned on, the control unit 4 of the receiving apparatus 1 sets the sensor ID of the data format to “0” in the downstream time slot B of the first frame F1 of the super frame SF, and sends a reply request message as the message Msg. Is sent to all the fire detectors 10. On the other hand, in the fire detector 10, immediately after the power is turned on, the control unit 13 closes the switch 16 to supply power to the wireless transmission / reception unit 12, and is in a continuous reception state until a synchronization signal (reply request message) is received. (Steps S1 and S2 in FIG. 6). If the reply request message can be received, the control unit 13 of the fire detector 10 opens the switch 16, cuts off the power supply to the wireless transmission / reception unit 12 and stops continuous reception (step S 3 in FIG. 6), and then built in the microcomputer. The started first timer, second timer, and third timer are started (step S4 in FIG. 6). The first timer is the time from the end of the downlink time slot B in the first frame F1 to the end of the superframe SF (for example, each of the frames F1 to F30 is 10 seconds, the superframe SF is 300 seconds, If the time slot in each of the downstream and upstream directions is 100 milliseconds, 300−0.1 = 299.9 seconds) is counted. In addition, the second timer is configured so that the upstream time slot Di (i = 1 to 99) individually assigned to each fire detector 10 from the time when the downstream time slot B ends in each frame Fk (k = 1 to 30). ) Is counted (for example, 0.1 × (number of upstream time slot Di i−1)). Further, the third timer is a time (for example, 10−0.1 = 9.9) from the time when the downlink time slot B ends in each frame Fk (k = 1 to 30) to the time when the frame Fk ends. Seconds).

  The control unit 13 of each fire detector 10 can determine the start time point of the upstream time slot Di assigned to itself by the end of the counting of the second timer, and the assigned upstream time slot. A response message to the reply request message of the receiving apparatus 1 is transmitted from the wireless transmission / reception unit 12 by Di, and then a fourth timer built in the microcomputer is started (steps S5 and S6 in FIG. 6). The fourth timer is a time from the end time of the uplink time slot Di assigned to itself in a certain frame Fk to the start time of the uplink time slot Di assigned to itself in the next frame Fk + 1 (for example, 10−0.1 = 9.9 seconds).

  On the other hand, the control unit 4 of the receiving device 1 receives a response message returned from each fire detector 10 in the upstream time slots D1 to D99 in the first frame F1 that has transmitted the reply request message. The content of the response message is the presence or absence of an abnormality in the fire detector 10 (for example, the battery voltage drops below a threshold value or the malfunction of the sensing unit 11), and the fire detector returns an abnormal response message. The control unit 4 of the receiving device 1 displays ten sensor IDs on the display operation unit 3 to notify the system administrator.

  When the third timer expires, the control unit 13 of the fire detector 10 closes the switch 16 and operates the wireless transmission / reception unit 12 to receive the downlink time slot B in the second frame F2, and the third timer The timer is started again (steps S7 and S8 in FIG. 6). Further, the control unit 13 compares the number of transmissions of the response message with the number of continuous transmissions notified from the receiving device 1 and stored in the nonvolatile memory (step S9 in FIG. 6). When the timer No. 4 expires, that is, as shown in FIG. 1, the response message having the same content is again transmitted in the uplink time slot Di (D1 to D3 in the illustrated example) assigned to itself in the second frame F2. It transmits (steps S11 and S6 in FIG. 6), and retransmits the response message having the same content until the number of continuous transmissions is reached (steps S6 to S11 in FIG. 6). Further, the control unit 13 of the fire detector 10 transmits a response message as many times as the number of continuous transmissions, and then opens the switch 16 until the first timer expires to stop the operation of the wireless transmission / reception unit 12 (step S10 in FIG. 6). ) When the first timer expires and the next superframe SF is started, the switch 16 is closed again to operate the wireless transmission / reception unit 12 to receive the downlink time slot B in the first frame F1 (see FIG. 6 step S12), the first to third timers are started and the above-described processing is repeated for each superframe SF.

  Next, the operation when a fire is detected by any of the fire detectors 10 will be described with reference to the flowchart of FIG. 7 and the time chart of FIG. The following process performed by the control unit 13 of the fire detector 10 when a fire is detected is an interrupt process (subroutine) for the above-described process (main routine shown in the flowchart of FIG. 6) that is always repeated.

  The control unit 13 of the fire detector 10 determines whether the second timer is counting when the detection unit 11 detects a fire (step S1 in FIG. 7). In other words, if the second timer is counting, the uplink time slot Di assigned in the frame Fk has not yet passed, so the uplink direction assigned to the own device when the second timer ends. The fire detection information is transmitted as a message Msg to the receiving device 1 through the time slot Di, and the fourth timer is started after the transmission (steps S2 and S3 in FIG. 7). In addition, if the second timer is not counting, the uplink time slot Di assigned in the frame Fk has already passed, so the control unit 13 of the fire detector 10 That is, the fire detection information is transmitted as the message Msg to the receiving device 1 by the uplink time slot Di assigned in the next frame Fk + 1, and the fourth timer is started after the transmission (steps S8 and S3 in FIG. 7).

  The control unit 13 of the fire detector 10 that has transmitted the fire detection information closes the switch 16 when the third timer expires and operates the wireless transmission / reception unit 12 to operate the downstream time in the next frame Fk + 1 (or Fk + 2). The slot B is received and the third timer is started again (steps S4 and S5 in FIG. 7). Further, the control unit 13 compares the number of transmissions of the fire detection information with the number of continuous transmissions notified from the receiving device 1 and stored in the non-volatile memory (step S6 in FIG. 7), and if the number of continuous transmissions has not been reached. When the fourth timer expires, that is, in the next frame Fk + 1 (or Fk + 2), the fire detection information is transmitted again in the upstream time slot Di assigned to itself (steps S8 and S3 in FIG. 7). The fire detection information is retransmitted until the number of continuous transmissions is reached (steps S3 to S8 in FIG. 7). If the number of transmissions of the fire detection information reaches the number of continuous transmissions, the control unit 13 ends the process of transmitting the fire detection information and returns to the main routine (flowchart in FIG. 6).

For example, when having detected a fire in a frame F1 fire detector 10 _2, 10 ₃ is the head of two of the three sets of the fire detector 10 _1, 10 _2, 10 ₃ as shown in FIG. 8, uplink allocated in the frame F2, F3 which continuously for continuous transmissions times from the fire detector 10 ₂ in the next frame F2 of the uplink time slot D2 of at the time of sensing the fire allocated to the own vessels has already passed The fire detection information is transmitted in the time slot D2, and when the fire is detected, the upstream time slot D3 assigned to the own device has not yet elapsed, and the fire detector 10 ₃ continues from the frame F1 by the number of times of continuous transmission. Fire detection information is transmitted in the uplink time slot D3 assigned in the frames F1 and F2.

  As described above, in the present embodiment, the control unit 4 serving as a notification unit of the receiving device 1 controls each fire detector 10 in one superframe SF according to the number of fire detectors 10 included in the system. On the other hand, the number of times of continuous transmission that satisfies the condition (transmission time duty: less than 0.1%) that allows the total transmission time of wireless signals that are allowed to be less than or equal to a predetermined threshold is obtained to each fire detector 10 by wireless signals. Because the control unit 13 of the fire detector 10 transmits the response message and the fire detection information having the same contents from the wireless transmission / reception unit 12 by radio signals in the number of uplink time slots Di equal to the notified number of continuous transmissions. The message exchange between the receiving device 1 and the fire detector 10 can be reliably performed while satisfying predetermined conditions. In addition, since the control unit 4 of the receiver 1 automatically obtains the optimum number of continuous transmissions for the system and notifies each fire detector 10, there is an advantage that the construction work becomes easy.

  By the way, when the response message is continuously transmitted to all the fire detectors 10 included in the system as described above, the traffic increases due to the unnecessary continuous transmission, which may hinder the transmission of the fire detection information. is there.

  Therefore, the signal intensity of the radio signal received in each uplink time slot Di is detected in the radio transmission / reception unit 2 of the receiving apparatus 1, and only for the fire detector 10 whose detected signal intensity is lower than a predetermined threshold value. The control unit 4 of the receiving device 1 notifies the number of times of continuous transmission and continuously transmits a response message, and only the fire detector 10 whose signal strength is lower than a predetermined threshold transmits the response message a plurality of times. If a response message is returned only once in the fire detector 10 whose strength is higher than a predetermined threshold value, it is possible to eliminate unnecessary continuous transmission and reduce traffic in periodic message exchange. However, the response message may be sent to the fire detector 10 whose signal strength is higher than the predetermined threshold value a plurality of times. In this case, the fire detector 10 whose signal strength is lower than the predetermined threshold value may be used. It is necessary to relatively increase the number of continuous transmissions.

  In the present embodiment, when a fire is detected by the fire detector 10, it is displayed on the display operation unit 3 of the receiving device 1 to notify the system administrator. For example, a plurality of receiving devices 1 are provided. Is connected to the central monitoring board by wire, and the fire detection information received by the receiving device 1 is relayed to the central monitoring board by wired communication, and necessary countermeasures are taken in the central monitoring board (for example, issuing a fire alarm or reporting to the fire department) Etc.).

It is a time chart for demonstrating the operation | movement of the periodic message exchange of embodiment of this invention. It is a system block diagram same as the above. (A) is a block diagram of a fire detector in the same as above, (b) is a block diagram of a receiving device. It is explanatory drawing of the data format in the same as the above. It is a block diagram of the super frame in the same as the above. It is a flowchart for demonstrating the operation | movement of the periodic message exchange same as the above. It is a flowchart for demonstrating the operation | movement at the time of the fire detection in the same as the above. It is a time chart for demonstrating the operation | movement at the time of the fire detection same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Receiver 10 Fire detector 11 Sensor 12 Wireless transmitter / receiver 13 Controller

Claims (2)

A plurality of fire detectors for detecting a fire, and a receiver for performing wireless communication using radio waves as a medium between the fire detectors;
The fire detector is composed of a sensing means for detecting a fire by detecting temperature change and smoke generated by the fire, a wireless transmitting / receiving means for transmitting and receiving a radio signal to and from the receiving device, and at least a sensing means for fire. Control means for controlling the wireless transmission / reception means when detected to transmit the fire detection information by a wireless signal,
The receiving device includes a wireless transmission / reception means for transmitting / receiving a wireless signal to / from the fire detector, and a control means for controlling the wireless transmission / reception means and obtaining fire detection information from the wireless signal received by the wireless transmission / reception means,
The control means of the receiving device periodically transmits a transmission request message for requesting a predetermined response to all fire detectors from the wireless transmission / reception means as a wireless signal,
The control unit of the fire detector returns a predetermined response message indicating the operation state of the own device when receiving the transmission request message to the receiving device by a wireless signal from the wireless transmission / reception unit,
The control means of the receiving device and the fire detector includes one downstream time slot from the receiving device to the fire detector, and a plurality of upstream directions from the fire detector assigned to each fire detector to the receiving device. A fire alarm system for exchanging a transmission request message and a response message in a super frame in which a plurality of frames composed of time slots are collected,
The control unit of the fire detector transmits a response message of the same content from the wireless transmission / reception unit in the uplink time slot assigned to the unit every plural frames until the number of continuous transmissions notified from the receiving device is reached. Send in
Depending on the number of fire detectors included in the system, the receiving device determines that the total transmission time of radio signals allowed for each fire detector within one superframe is below a predetermined threshold. What is claimed is: 1. A fire alarm system comprising notification means for obtaining a number of times of continuous transmission satisfying a condition to notify each fire detector by a radio signal. The receiving device includes signal strength detection means for detecting the signal strength of the wireless signal received by the wireless transmission / reception means,
2. The fire alarm system according to claim 1, wherein the notification means of the receiving apparatus relatively reduces the number of continuous transmissions of the fire detector whose signal intensity detected by the signal intensity detection means is relatively high.

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