JP2775064B2 - Method and system for detecting disconnection of sensor line in fire monitoring system using multiplex transmission - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention uses a multiplex transmission and simplifies signal processing on a relay side for monitoring and controlling an addressed sensor in a fire monitoring system. The present invention relates to a fire monitoring method for detecting disconnection of a line and a fire monitoring system that can implement the method.

[Related Art] Recently, with the rise of buildings and the like, various fire monitoring systems have been developed and proposed which output quick and accurate warnings at the time of fire occurrence and provide prompt evacuation guidance. I have.

FIG. 9 shows the basic configuration of an intelligent fire monitoring system that has recently been in the spotlight among such fire monitoring systems.

Referring to the drawing, the fire receiver 100 and the repeater 200
Are connected via a multiplex signal line 1 and a sensor power supply line l2, a sensor line l3 is derived from each repeater 200, and a different address is assigned to the derived sensor line l3. Connected to a plurality of sensors SA.

Here, the sensor SA to which the address is assigned is composed of a smoke and heat sensor, and multiplexes the detected smoke information such as the smoke concentration and temperature in multiple stages together with the set address and an analog signal which is divided into multiple levels. It is configured to reply in the form of
A detector line l3 derived from each repeater 200 has a detector line l2 from a detector power supply 104 provided on the fire receiver 100 side.
Is configured to receive power supply via the.

In such a fire monitoring system, a fire receiver
CP according to the control program stored in the memory 106 of the 100
When a multiplexed signal with a repeater address is transmitted from the control means 102 composed of U to the multiplexed signal line 1 through the multiplexed transmission control unit 101 in a polling system, the multiplexed transmission control unit 202 of the repeater 200 having the same address is transmitted. Then, the control means 204 decodes the received multiplex signal to operate the multiplex transmission control section 203, and sends a sensor monitor signal to which a sensor address is added in the form of a multiplex signal to the sensor line l3. From the sensor SA that received the signal, a reply signal with the detected fire information added to the sensor address is returned in the form of a multiplex signal, and the control means 204 provided on the repeater 200 side decodes this reply signal, The alert from the sensor is discriminated, and when the alert from the sensor is confirmed, the multiplex transmission control unit 202 is operated again to send the signal to the fire receiver 1 side.

In this manner, the fire receiver 1 that has received the sensor alert is configured to operate the fire alarm means to generate a fire alarm.

However, in such a fire monitoring system, the multiplexed signal transmitted from the fire receiver 100 is converted into a completely different multiplexed signal inside the repeater 200 and transmitted to each of the sensors SA connected to the sensor line l3. Conversely, since the return signal from each sensor SA is converted into a different multiplexed signal inside the repeater 200 and returned to the fire receiver 1, the repeater 20
It is necessary to provide the advanced signal processing function to 0, and the signal processing function in the system is distributed for each repeater 200, which has been a factor of reducing the reliability of the system.

Also, apart from such a problem, when the sensor line l3 is disconnected for some reason, the return signal from the sensor SA connected to the terminal side from the disconnection point stops,
It is not possible to distinguish between a disconnection of the sensor line 13 and a failure of the sensor SA, and this also reduces the reliability of the system.

[Problems to be Solved by the Invention] Therefore, the present inventor simplified the configuration and functions of the repeater, centralized the functions on the fire receiver side, reduced the total cost of the entire system, and improved the reliability. Although a fire monitoring method and a fire monitoring system in a fire monitoring system using multiplex transmission that can be used have been previously proposed, the present invention proposes a further improved invention of the proposed invention, and in particular, detects a disconnection of a sensor line. It is an object of the present invention to provide an improved fire monitoring system provided with such a method and such a disconnection detection function.

[Means for Solving the Problems] The method of the present invention proposed to achieve the above object is as follows.
A fire receiver and a plurality of repeaters are connected by a multiplex signal line, and at least one of these repeaters is led to a sensor line to which a plurality of sensors assigned an address are connected. At the end of the line is connected a terminator that continuously performs a suction operation of the current supplied to the sensor line for a predetermined time when a voltage supply of a predetermined level or more is received. A fire monitoring system using multiplex transmission, in which power is supplied from a detector power supply on the fire receiver side through a detector power supply line, wherein the relay side from the fire receiver side is polled by a polling method. Transmitting a transmission switching signal of a specific multiplex transmission level designating the repeater address via the multiplex signal line,
On the repeater side receiving this transmission switching signal, the monitoring signal specified by the sensor address transmitted from the fire receiver side via the multiplex signal line following the switching signal is transmitted according to the sensor line. Level, and send it to the sensor line as it is. The reply signal returned from the sensor with address that received the monitoring signal to the sensor line is converted again to a specific multiplex signal level by the repeater, and the above fire is caused. In the fire monitoring system configured to perform the basic operation of returning to the receiver side, a continuity test in which the repeater address is specified via a multiplexed signal line by a polling method from the fire receiver side to the repeater side is started. A signal is transmitted, and the repeater receiving the continuity test start signal operates the terminator from the voltage level supplied to the sensor side from the above sensor line to the normal monitor level. After the voltage is lowered for a predetermined time to a level at which the sensor is not activated, the level is returned to the level at the time of monitoring the sensor. The voltage level occurring in the sensor line is detected during each period from the start of voltage supply at the time of monitoring the detector to the end of the current sink operation of the terminator, and the detected voltage level is initially If the detection timing is lower than the predetermined reference level at the monitoring timing and higher than the predetermined reference level at the next monitoring timing, the detector line is determined to be disconnected, and a disconnection detection signal is returned to the fire receiver side. Then, from the fire receiver side receiving the disconnection detection signal, a similar continuity test start signal is sent to the above-mentioned repeater side, and thereafter the fire receiver side becomes the same as the repeater side in the same manner. When receiving the disconnection detection signal of a predetermined number of times, the fire receiver is characterized by generating an alarm signal for informing the disconnection of the sensor lines.

The fire monitoring system of the present invention, which is also proposed at the same time, includes a relay having a detector line configured to supply power from a detector power supply provided on the fire receiver side via a detector power supply line. When connected to a fire receiver via a signal line and receiving a voltage of a predetermined level or more at each end of these sensor lines, the terminal absorbs the current supplied to the sensor lines for a predetermined time. Multiplex transmission is configured by connecting a terminator that is to be performed continuously, and configured to transmit and receive a multiplexed signal by the polling method from the fire receiver to the repeater side to determine disconnection of the sensor line. In the fire monitoring system used, the fire receiver monitors a sensor line derived from a repeater in the system and a sensor connected to the sensor line, and at least when the alarm is issued and the number of times of detection. When a disconnection is determined, an alarm signal is output.Therefore, each relay in the system is connected via a multiplex signal line, and the relays are monitored to monitor the sensor lines of these relays. A test start signal is transmitted to the multiplex signal line, and the multiplex transmission control unit for receiving the disconnection detection signal returned from the repeater and the multiplex transmission control unit are operated according to a preset control program. While performing the necessary processing by decoding the multiplex signal including the disconnection detection signal received by the multiplex transmission control unit, the control means, and connected to each repeater in the system via a sensor power line, At least a sensor power supply for supplying power at a level required for the alarming operation of the sensor, wherein the relay is connected to the fire receiver via a multiplex signal line. A multiplex transmission control unit for receiving a test start signal and returning a disconnection detection signal to the fire receiver, and an address setting for setting an address added to a multiplex signal transmitted and received between the fire receiver and the fire receiver. And a detector line supplied with power from a detector power supply on the fire receiver side through a detector power supply line, and the multiplex signal control unit is activated when a continuity test start signal is received from the fire receiver. The voltage level supplied to the sensor line is reduced to a non-operation level of a terminator connected to the sensor line for a predetermined time, and after the predetermined time has elapsed, the voltage supplied to the sensor line is reduced. Continuity test means for restoring the voltage to be returned to a normal monitoring level, and a voltage level occurring in the sensor line during the two times of voltage supply by the continuity test means, Level determination means for comparing and determining the extracted voltage level with a predetermined reference level, and presence / absence of disconnection of the sensor line based on a determination signal from the level determination means for returning a test determination signal to the fire receiver. And a control unit for sending a test determination signal to the multiplex transmission control unit.

According to the third aspect of the present invention, the continuity test means required for the repeater is interposed between the sensor power supply line and the sensor line, and the sensor power supply line is always used for the alarm operation of the sensor. A voltage adjustment circuit that supplies a constant voltage that is lower by a certain level than during normal monitoring to the sensor line when the sensor line is alerted,
A switching circuit for interrupting, for a predetermined time, a supply operation of the voltage adjustment circuit to the sensor line when receiving a voltage cutoff signal from the control means that has decoded the multiplex signal transmitted from the fire receiver side. It is composed.

[Operation] In the method of the present invention, a continuity test signal is sent from the fire receiver side to the repeater side, and the repeater side receiving this continuity test signal reduces the voltage level supplied to the sensor line for a fixed time. The disconnection state of the sensor line can be detected by a simple method.

In this way, when the continuity test is performed on the repeater side and a disconnection is detected, a disconnection detection signal is sent to the fire receiver side in the form of a test determination signal, and the fire receiver side receiving this signal transmits the disconnection detection signal. The disconnection signal is once released.

When the above operation is repeated and a similar disconnection detection signal is continuously sent to the fire receiver side and reaches a predetermined number, the fire receiver side first determines the disconnection of the detector line and gives an alarm means. Activate

Further, according to the system of the present invention, as a basic control operation for monitoring the address-added sensor, the repeater simply performs level conversion on the multiplexed signal transmitted from the fire receiver to determine the occurrence of the alarm. However, for a general sensor, a change in the voltage level generated in the sensor line is monitored by the repeater to determine whether the alarm has occurred.

Further, the disconnection detection of the sensor line is performed by detecting a change in the voltage level generated in the sensor line when the voltage level supplied to the sensor line is changed for a predetermined time by the continuity test means provided on the repeater side. Monitored to determine.

Embodiment An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

(Configuration of Fire Monitoring System) FIG. 1 is a block diagram showing a fire monitoring system incorporating a main part configuration of the present invention, wherein a fire receiver 1 and each of the repeaters 2. A plurality of sensors SA, which are set with a sensor address, and an address are set on a sensor line l3 connected to the signal line 1 via a sensor power supply line l2 and derived from each of the repeaters 2. Are connected together, and a terminator 4 described later is connected to the end of the sensor line 13.

In such a system, each of the sensors SA and S connected to the detector power supply line l2 is connected to the detector power supply on the fire receiver 1 side.
Power is supplied from 14.

The fire receiver 1 generates a multiplex signal in accordance with the multiplex transmission control unit 11 and the control program stored in the memory 16, and processes the multiplex signal received by the multiplex transmission control unit 11 to generate a necessary control signal. A control means 12 constituted by a CPU for outputting, and an alarm means 13 for receiving an abnormal signal and generating an alarm when the disconnection of the sensor line 13 and the alarm of the sensors S and SA are determined in the control means 12. The I / O port 15 for outputting a control signal to a control terminal device (not shown) provided outside according to a control signal from the control means 12 and a sensor line l3 through a sensor power line l2. Detector SA
.., S... Are provided with a detector power supply 14.

One of the repeaters 2 is a multiplex transmission control unit 22 for transmitting and receiving a multiplex signal of a specific level to and from the fire receiver 1, and a multiplex signal received by the multiplex transmission control unit 22 is decoded to be preset. A control means 26 configured by a CPU for performing necessary control according to a control program; an address setting unit 21 for setting an address unique to the repeater for multiplex transmission processing; and a continuity test described later and a monitoring of a general sensor. Sensor power line l3
Control means for comparing and judging the voltage level occurring in the
A level discriminator 28 that outputs a discrimination signal to 26, and a sensor line
A continuity test means 24 for supplying a voltage of a predetermined level to the sensor line l3 in order to perform a continuity test of l3 according to a procedure described later.
And converts the multiplex signal of a specific level received by the multiplex transmission control unit 22 into a signal level suitable for the sensor line l3, and outputs the multiplexed signal to the sensor SA having an address set.
A level conversion control unit 23 having a configuration described below, which converts the return signal from the multiplex transmission control unit 22 to an acceptable level,
The multiplex transmission control unit 22 and the insulated transmission circuit 25 that performs signal transmission and reception between the level conversion control unit 23 and the power supply separately from the power supply, and supply of the sensor power supply 14 through the sensor power supply line l2. Multiplex transmission control unit under the control of the control means 26
The configuration includes a transmission switching circuit 27 that allows or prohibits signal transmission between the level conversion control unit 22 and the level conversion control unit 23.

In the fire monitoring system having such a configuration, the repeater 2 receives a multiplex signal transmitted from the fire receiver 1 at a specific multiplex transmission level, and detects a disconnection of the sensor line l3.
Each control is performed, such as the alarm monitoring of a sensor with an address and the alarm monitoring of a general sensor without an address.

(Basic Operation of Fire Monitoring System) Next, each control operation in the fire monitoring system will be described.

(1) Alarm monitoring of a sensor with an address The fire receiver 1 multiplexes a transmission switching start signal of a specific level assigned a repeater address through a multiplex transmission control unit 11 according to a control program stored in a memory 16. When sequentially transmitted to the signal line 1 by the polling method, in each of the repeaters 2... Connected via the multiplexed signal line 1, the multiplexed transmission control unit 22 receives the multiplexed signal, and the control unit 26 controls the address setting unit. Check with the address set in 21.

As a result, in the repeater 2 whose addresses match, after a delay of a predetermined time TO (time sufficient for the CPU of the sensor side to be in the operating state), the gate is sent from the control means 26 to the transmission switching circuit 27. A signal is transmitted, and transmission / reception of a multiplex signal between the multiplex transmission control unit 22 and the level conversion control unit 23 via the insulated transmission circuit 25 is enabled to enter a multiplex signal transmission period. In this way, when the multiplex signal transmission period starts, the multiplex transmission control unit 22 receives the detector monitoring signal with the sensor address sequentially transmitted from the fire receiver 1 via the multiplex signal line 1. After that, the signal is transmitted to the level conversion control unit 23 through the transmission switching circuit 27 and the insulated transmission circuit 25.

In the level conversion control unit 23, after lowering the voltage level of the sensor line l3 from the normal monitoring level VCC to the VDD level, the amplitude is turned ON and OFF between VDD and V2 with the peak of VDD. A multiplex signal of a level adapted to the sensor line 13 is sent to the sensor line 13.

Thus, such a multiplex signal is transmitted to the level conversion control unit 23.
Is sent to the sensor line l3 through the sensor, a sensor return signal is returned from the addressed sensor SA.
This return signal is sent to the level conversion control unit via the sensor line l3.
When received at 23, the signal is sent to the multiplex transmission control unit 22 through the insulated transmission circuit 25 and the transmission switching circuit 27. The multiplex transmission control unit 22 converts the signal into a multiplex signal of a specific level again and sends it out to the multiplex signal line 1.

In such a fire monitoring system, the sensor return signal from the addressed sensor SA includes, in addition to the address assigned to the sensor SA, when the sensor SA is a smoke or heat sensor. , And an analog signal corresponding to the density and temperature level detected by the sensor. The analog signal is, for example, a signal obtained by classifying the smoke density into stages.

On the fire receiver 1 side, the control means 12 decodes the sensor return signals sequentially sent from the addressed sensors SA... When it is determined that the alarm has been issued, a fire detection signal is output to the alarm means 13 to notify a fire.

Thus, when communication with all the sensors SA connected to the sensor line 13 of the accessed repeater 2 is completed, the fire receiver 1 sends a transmission switching end signal of a specific level via the multiplex signal line 1 to the repeater. When the repeater 2 receives the transmission switching end signal, the control means 26 stops the operation of the transmission switching circuit 27 and ends the multiplex signal transmission period. As a result, the voltage of the sensor line 13 is Level is VCC again
Return to.

In this manner, between the fire receiver 1 and each of the repeaters 2, the transmission of the monitoring signal and the reception of the reply signal are sequentially and repeatedly performed by the polling method, and each time the repeater 2 is accessed, an address is added. From the detected sensor, a signal (the above-described analog signal) corresponding to the level detected by the sensor is returned to the fire receiver 1 side (the above-described FIGS. 2A to 2C). See time chart).

Further, as understood from the above description, during the monitoring period for such an addressed sensor SA, the repeater 2
On the side, the multiplex signal transmitted from the fire receiver 1 at a specific multiplex transmission level is converted into a level corresponding to the sensor line l3, and the return signal returned from each sensor SA is controlled by the control means in the repeater 2. In 26, the data is sent to the multiplex transmission control unit 22 without any decoding. That is, the repeater 2 performs only the level conversion of the signal transmitted and received between the multiplexed signal line 1 and the sensor line 13, and all the decoding of the return signal is performed on the receiver 1 side. Therefore, in such a fire monitoring system, not only the function of the repeater 2 can be simplified and the total cost of the system can be reduced, but also the central fire receiver side can collectively centralize the management.

(2) Alert Monitoring of General Sensor Next, a control operation of the general sensor during a monitoring period will be described.

The general sensor S to which no address is assigned normally opens the sensor line l3 and, when an alarm is issued, performs an operation of short-circuiting the sensor line l3 via a predetermined resistance component.
This side can detect this condition by monitoring the voltage level occurring in the sensor line 13 and determining that the level has dropped from the normal monitoring level to the alert level of the sensor.

When the fire receiver 1 transmits a monitoring start signal of a specific level specifying a repeater address via the multiplex signal line 1, the repeater 2 having the same repeater address enters a monitoring period of the general sensor.

During the monitoring period, the level discriminating unit 28 determines the voltage level of the sensor line 13 and the reference voltage set in the level discriminating unit 28 (a fixed level that is reduced by the operation of the voltage adjusting circuit 23 when the sensor S is informed. (Set to be slightly larger) to determine whether or not the general sensor S is alerted.

That is, when the voltage level of the sensor line 13 drops below the reference voltage level, the sensor S connected to the sensor line 13 is alerting, and when the detected voltage level exceeds the reference level, the alarm is issued. Judge that there is no information.

The control means 26 receives the determination signal from the level determination means 28,
The multiplexed signal is fetched through the insulated transmission circuit 25, and the fetched discrimination signal is sent to the multiplex transmission control unit 22 to be output to the multiplex signal line 1. It is decoded by the means 12 and the alarm of the sensor S is discriminated.
A fire detection signal is output by 13 and fire notification is performed.

When the monitoring of the general sensor S connected to the sensor line 13 is completed in this way, the fire receiver 1 transmits a monitoring end signal of a specific level to the repeater 2 via the multiplex signal line 1 and relays the signal. In response to the monitoring end signal, the detector 2 ends the capture of the discrimination signal by the control means 26, and ends the monitoring period of the general sensor.

The alert monitoring of the general sensor may be performed until the repeater receives the transmission start signal and enters a multiplex transmission period for monitoring the sensor. More easily.

(Structure of Repeater) Next, the structure of the repeater and the terminator required for implementing the short-circuit detection method of the present invention will be described in more detail.

FIG. 3 shows the repeater 2 used in the system of the present invention.
1 is shown in a block diagram, and the same parts as those in FIG. 1 are denoted by the same reference numerals.

The repeater 2 is connected to a rectifier circuit 22a composed of a bridge diode for full-wave rectifying the multiplex signal transmitted from the fire receiver 1 side, and to the terminals NA and NB of the multiplex signal line 1,
A multiplex signal receiving circuit 22b for receiving a multiplex signal transmitted from the fire receiver 1 at a specific multiplex signal level;
Alternatively, the multiplex transmission control unit 22 includes a multiplex signal transmission circuit 22c that converts a multiplex signal transmitted through the level conversion control unit 23 into a multiplex signal of a specific level and transmits the multiplex signal to the fire receiver 1. The pulsating current component rectified by the rectifier circuit 22a is sent to the constant voltage power supply circuit 22A, and stabilized power is supplied from the constant voltage power supply circuit 22A to the control unit 26 side. .

Further, the level conversion circuit 23 is a monitoring signal level conversion circuit 23a that converts the multiplexed signal transmitted from the multiplexed signal reception circuit 22b to a multiplexed signal level suitable for the sensor line l3,
And a return signal level conversion circuit 23b for converting a return signal from the sensor SA with the address to a signal level for sending to the multiplex signal conversion circuit 22c of the multiplex transmission control unit 22.

The level conversion control unit 23 and the multiplex transmission control unit 22 having such a configuration are connected in a state in which signal transmission is possible via the insulated transmission circuit 25 and the transmission switching circuit 27. The output side of the circuit 23a and the input side of the return signal level conversion circuit 23b are configured to be connected to a sensor line 13 via a terminal LN.

One continuity test means 24 is connected to terminals F,
The sensor power supply 14 is supplied from FG,
A voltage regulating circuit is configured by combining a current limiting circuit 24a that outputs an output voltage Vcc equal to the constant voltage power supply circuit 24b connected in parallel via the diode D1 and the current limiting circuit 24a. Adjustment circuit to sensor line l3
The output to is controlled or interrupted by controlling the switching circuit 24c.

Further, the level determination unit 28 has a reference voltage 28b,
A determination signal is output by comparing and determining the voltage level generated at the terminal LN of the sensor line l3 with the reference voltage 28b.
It is configured to be input to 26.

Here, the reference voltage 28b is set slightly higher than the voltage level (the output level of the constant voltage power supply circuit in this embodiment) generated in the sensor line 13 when the general sensor S issues an alarm. Therefore, when the general sensor S is fired,
An “L” level determination signal is output.

(Configuration of Terminator) Next, the configuration of the terminator will be described.

As shown in the circuit example of FIG. 4, the terminator 4 uses a reference voltage (about 4 volts) as a threshold, and when a higher voltage level is input to the input terminal IN, the output terminal
It has a voltage detection circuit IC10 that opens OUT and conversely short-circuits the output terminal OUT to the ground level when the input voltage is lower than the threshold.

To explain the configuration together with the operation, when at a normal monitoring level, a voltage of VCC (about 28 volts) is supplied to the sensor line l3, and this voltage is connected to a bridge diode.
Since the voltage is depolarized by BD and divided by resistors R10 and R11 and applied to the input terminal IN of the voltage detection circuit IC10, this voltage level exceeds the threshold value (about 4 volts), and therefore the output terminal OU
T is released, and the capacitor C is charged through the resistors R10, R12, R13 and the transistor Q10.

When the continuity test period starts in this state, the first time T (approximately
30 ms), the voltage level of the sensor line l3 is VDD
(Approximately 12 volts) (see FIG. 5 (a)), so that the divided voltage level by the resistors R10 and R11 of the terminator 4 becomes lower than the threshold value, and the output terminal OUT of the voltage detection circuit IC10 is grounded. Shorted to the level.

As a result, the electric charge charged in the capacitor C is output to the output terminal.
Discharged instantaneously (about 3 milliseconds) via OUT, diode D and resistor R13.

Next, the voltage of the sensor line l3 becomes the normal monitoring level VCC.
Then, the voltage level of the input terminal IN of the voltage detection circuit IC10 exceeds the threshold value, the output terminal OUT is opened, and the capacitor C is connected to the resistors R10, R12, R13 and the transistor Q.
Charged through 10.

Since the charging time T 'is longer than the discharging time (about 60 milliseconds), the transistors Q10 and Q11 are turned on during this time T', so that the detector line 13 is terminated by the resistor R14 and the sink current (about 30mA) (see Fig. 5 (b)),
The voltage level of the sensor line 13 becomes V1 (about 17 volts).

Then, when the transistors Q10 and Q11 turn off after the time T ', the level rises again to the same level as at the time of monitoring (see FIG. 5 (a)).

In other words, such a terminator 4 charges the capacitor when the voltage level of the sensor line l3 is higher than the predetermined operation level and flows the sink current. When the voltage level falls below the predetermined operation level, the terminator 4 instantaneously switches the capacitor. In the present embodiment, the suction current flowing at this time is set to be equal to the notification current at the time of notification of the general sensor.

The threshold of the operating voltage level of the terminator 4 may be set to 17 V or less in the case of the embodiment.

(Continuity Test Operation) Next, a control operation during the continuity test period will be described.

For this continuity test, it is necessary to connect the terminator 4 to the end of the sensor line l3. As described above, the terminator 4 has the voltage level of the sensor line l3 at the level during normal monitoring.
When the voltage is lowered from VCC to a predetermined level VDD at which the terminator does not operate, and is returned to the level VCC at the time of monitoring again, the sink current (general sensor S is applied to the sensor line 13 for a predetermined time T '). It has a function to force the same current level as when the alarm is issued.

In the method of the present invention, a continuity test is performed by using such a terminator 4.
Referring to the time chart of FIG. 6 and FIG. 6b, when the fire receiver 1 transmits a continuity test start signal with a repeater address via the multiplex signal line 1, the fire receiver 1 In the same way as the general sensor monitoring period, the repeater 2 whose repeater address matches matches enters the continuity test period.

That is, the control means 26 outputs a cutoff signal for a predetermined time T to the level conversion control unit 23 through the insulated transmission circuit 25 to cut off the supply of the sensor power to the sensor line l3, After the voltage of l3 is reduced from the normal monitoring level VCC to a predetermined level VDD, the supply of the sensor power is restarted (see FIG. 6A).

Then, if there is no disconnection in the sensor line l3 and it is normal, the terminator 4 operates and the sink current flows through the sensor line l3 for a predetermined time T ', so that the voltage generated in the sensor line l3 is Stays at level V1 without rising to VCC.

When the suction operation of the terminator 4 is completed, the voltage of the normal monitoring level is supplied to the sensor line 13 so that the voltage returns to VCC (see FIG. 6a).

On the other hand, if the sensor line 13 is disconnected in the middle, the sink current by the terminator 4 disappears, and when the sensor power of the normal monitoring level VCC is supplied again after the time T, the sensor The voltage level of the line 13 immediately returns to VCC (see FIG. 6 (b)).

That is, if the continuity test detection signals at both the first monitoring timing and the second monitoring timing are at the “L” level, the sensor line 13 is normal, and the continuity test detection signal is at the “L” level at the first monitoring timing. If the level is "H" at the second monitoring timing, it is determined that a disconnection has occurred in the sensor line l3.

The voltage level of this detector line l3 is
The control means 26 is monitored by the level determining section 28 having the reference voltage set to a voltage level between 1 and 1 after the time T1S (the first monitoring timing) and after the time T2S after outputting the cutoff signal. It is configured that the presence / absence of disconnection of the sensor line 13 is determined by taking in a later (second monitoring timing) determination signal.

Then, the control means 26 converts the determined continuity test detection signal into a corresponding multiplex signal, and outputs the multiplex signal to the multiplex signal line 1 through the multiplex transmission control section 22. Received by the unit 11, decoded by the control means 12, and outputs a control signal to an external control terminal device via the I / O port 15 when the disconnection is determined in accordance with the continuity test detection signal to notify a necessary disconnection alarm. And so on.

Next, the disconnection detecting method of the present invention will be described more specifically with reference to the above-described block diagram of the repeater and the terminator.

In the continuity test of the sensor line l3, it is necessary to connect a terminator having the above-described configuration to each end of the sensor line l3, and a continuity test is performed by connecting such a terminator. The operation at this time will be described with reference to the time chart of FIG.

When the fire receiver transmits a continuity test start signal of a specific level to which a repeater address is attached via the multiplex signal line 1, the repeater 2 having the same repeater address enters a continuity test period.

That is, the control means 26 operates the continuity test means 24 through the insulated transmission circuit 25 to lower the power supplied to the sensor line 13 for a predetermined time T from a normal monitoring level to a predetermined level. After that, it is returned to the normal monitoring level. Then, the terminator 4 operates to start sinking the current, and the sink current flows through the sensor line 13 for a predetermined time T ', so that the voltage level of the sensor line 13 becomes VC
If the current stops at V1 without returning to C and the suction operation by the terminator 4 ends and the suction current stops,
Will be returned to.

The voltage level of this detector line l3 is
The level is compared and determined by a level determining unit 28 having a reference voltage (lower than the operation level of the terminator) set to a voltage level between 1 and the control means 26 controls the voltage of the sensor line 13 A period in which the level is reduced to a level at which the terminator 4 is not operated (first monitoring timing), and a period from when the voltage level of the sensor line 13 is released to when the current sink operation by the terminator 4 is completed. The disconnection of the sensor line 13 is detected by taking in the determination signals obtained at (second monitoring timing) from the level determination unit 28, respectively.

That is, in such a method, the detector line at both the first monitoring timing and the second monitoring timing is used.
l3 voltage level becomes lower than the operation level of the terminator 4,
If the discrimination signal becomes lower than the operation level of the terminator 4 at the first monitoring timing and becomes [L] level and exceeds the operation level of the terminator 4 at the second monitoring timing and becomes [H] level,
It is determined that a disconnection has occurred in the sensor line l3.

Then, after the determination signal for determining the presence / absence of the disconnection of the sensor line 13 is given the address set by the address setting unit 21 by the control means 26, the multiplex transmission control unit
The signal is sent to the multiplexed signal line 1 again.

On the fire receiver 1 side, the control unit 12 decodes the multiplex signal transmitted from the multiplex transmission control unit 22 of the repeater 2 in this manner, and determines whether or not the wire is broken. A control signal is output to an external control terminal via the / O port 15 to provide a necessary disconnection alarm.

FIG. 7 is a configuration diagram of an internal circuit showing a main part of the repeater.

This internal configuration diagram has a configuration excluding a multiplex transmission control unit, a control unit including a CPU, and an address setting unit.

The continuity test operation will be further described with reference to FIG.
When a continuity test start signal with a repeater address is input from the fire receiver 1, the repeater 2 having the same address decodes the signal with the CPU, sends out a cutoff signal, and outputs a photocoupler of the insulated transmission circuit 25. 25a for time T (about 30 ms)
Just turn on.

As a result, the transistor Q3 is turned on, the transistor Q4 is turned off, and the transistors Q5 and Q6 are turned off, so that the power supply V supplied to the terminal LN through the transistors Q5 and Q6 is turned on.
CC and power supply VEE are cut off, and terminal LN
1, level through transistors Q1, Q2 and diode D2
VDD (about 12 volts) is supplied.

Next, when the time T elapses, the control means 26 releases the cutoff signal, so that the photocoupler 25a is turned off. As a result, the transistors Q5 and Q6 are turned on, and the power supply VCC and the power supply VE are turned off.
E is supplied to the terminal LN again.

However, at this time, if there is no disconnection in the sensor line l3 and it is normal, a suction current (about 30 mA) flows through the terminator 4, so that the voltage of the terminal LN becomes V1 (about 17 volts), and the suction operation by the terminator 4 Is completed (after the elapse of time T ′: about 60
Millisecond), the voltage level of the terminal LN returns to the level of the power supply VCC again.

On the other hand, the level determination unit 28 of the repeater 2
The power supply VCC is divided by resistors R4 and R5, and has a reference voltage 28b of level ER (about 19 volts).

The comparator CMP2 monitors the voltage level of the terminal LN and transmits a test discrimination signal to the control means 26 through the photocoupler 25d. , (First monitoring timing
The output level of the comparator CMP2 is monitored during the period from the time when the voltage is returned to the normal monitoring level until the suction current operation by the terminator 4 is completed (second monitoring timing TS2).

Therefore, when the sensor line 13 is normally connected, the comparator CM at the time of the first and second monitoring timings is set.
The output levels of P2 are all "L" levels.

However, if the voltage applied to the sensor line l3 is changed as described above, and if a disconnection occurs in the middle of the sensor line l3, the sink current by the terminator 4 will not flow. Immediately returns to the level of the power supply VCC after the elapse of the time T. Therefore,
The comparator CMP2 outputs an “L” level during the first monitoring, and outputs an “H” level during the second monitoring.

The control means 26 reads the test discrimination signals at the time of the first monitoring and at the time of the second monitoring to determine disconnection, and outputs a disconnection detection signal to the fire receiver 1 through the multiplex transmission control unit 22.

Further, the repeater 2 having such a configuration also has a protection function when a short circuit occurs in the sensor line l3. Next, the short circuit protection operation will be described.

When a short circuit occurs in the sensor line l3, since the constant voltage power supply circuit 24b of the continuity test means 24 has low impedance, the power supply VEE flows through the short-circuited sensor line l3, and the constant voltage power supply circuit 24b is damaged. Or a burnout may occur at the short circuit of the sensor line l3.

For this reason, the occurrence of a short circuit is detected by the short circuit detection circuit 29a, and the short circuit holding circuit 29b is operated to forcibly lower the voltage level of the sensor line 13 to a predetermined level, thereby detecting the short circuit of the short circuit detection circuit 29a. And the transistor Q9 is turned on to lower the reference voltage level of the comparator CMP2 to substantially zero volts.

A short circuit occurs in the sensor line l3, and the voltage level of the sensor line l3 is equal to or longer than a predetermined time determined by the capacitor C1 and the resistor R6 of the short-circuit detection circuit 29a. If the voltage drops below the level determined by the diode ZD2), the transistor Q7 is turned on to turn on the transistor Q8, thereby turning off the transistor Q4, opening the bases of the transistors Q5 and Q6, and A diode connected to the collector of transistor Q8, while blocking VCC and power supply VEE from being supplied to sensor line l3 through terminal LN.
The voltage level of the terminal LN is forcibly reduced to a predetermined level via D5 and the resistor R9, and the transistor Q7 is turned on by itself to perform a short-circuit protection operation.

In such a state, since the transistor Q9 is turned on by turning on the transistor Q7, the reference voltage 28b of the comparator CMP2 is reduced to substantially zero volt, and the output of the comparator CMP2 continues to be "H". "
Level.

As described above, when the short circuit occurs in the sensor line l3 and the short circuit protection operation is being performed, when the continuity test start signal is input from the fire receiver 1 to the repeater 2, the case of the disconnection detection is performed. Similarly, the shut-off signal from the control means 26 turns off the transistors Q5 and Q6.However, since the transistors Q5 and Q6 are already turned off by short-circuit protection and the voltage of the terminal LN has dropped to a predetermined level, the comparator The output of CMP2 continues at the “H” level.

Therefore, at the first monitoring time T1S, the output of the comparator CMP2 becomes “H” level, and after the time T1 has elapsed, the control means 26
Even if the off operation of the transistors Q5 and Q6 is canceled due to the short circuit protection operation, the off state is continued.
The output of comparator CMP2 is still at "H" level.

The short circuit is detected by the control means 26 determining the "H" level conduction monitoring signal at the time of the first monitoring and the second monitoring, and a short circuit detection signal is output to the fire receiver 1 side.

On the other hand, the fire receiver 1 that has received the short-circuit detection signal transmits a recovery signal to the repeater 2 and drives a short-circuit recovery circuit (not shown) by the control means 26 for a predetermined time, thereby detecting the sensor. The line open contact 29c is opened and the relay contact 29d is closed to release the self-holding of the transistor Q7. In this way, when the short-circuit protection is activated again after the relay is released and the sensor line 13 is connected, the short-circuit detection signal is transmitted again to the fire receiver 1 by the same operation as described above, When this operation is repeated a predetermined number of times, the fire receiver 1 determines for the first time that the sensor line 13 is short-circuited and notifies the user.

Therefore, even if a short circuit occurs in the sensor line l3, the short circuit protection is activated immediately to prevent the destruction of parts and the burnout of the sensor line l3, and the short circuit is repeated after confirming the short circuit on the fire receiver 1 side. Since the notification is performed, a malfunction does not occur, and the reliability of the system can be improved.

Next, an operation in a multiplex signal transmission period in which a multiplex signal is transmitted and received between the fire receiver 1 and the sensor SA via the repeater 2 will be described.

Repeater 2 from fire receiver 1 via multiplex signal line 1
When a transmission switching start signal with an address is input to the repeater 2, the multiplexed signal is decoded by the control means 26 in the repeater 2 having the same address, and the photocoupler 25a of the insulated transmission circuit 25 is decoded.
Drive. By driving the photocoupler 25a, a current flows from the power supply VDD to the base of the transistor Q3 through the resistor R1, the transistor Q1, and the photocoupler 25a, so that the transistor Q3 is turned on and the transistor Q4 is turned off. Then, the base currents of the transistors Q5 and Q6 are cut off,
Connected terminal of sensor line l3 through transistor Q5
Power supply VCC supplied to LN and power supply VEE similarly supplied to terminal LN through transistor Q6 are cut off. As a result, the terminal LN receives the resistor R1 and the transistor Q from the power supply VDD.
The level VDD (approximately 12 volts) is supplied through 1, Q2 and the diode D2 to enter a transmission period of the multiplex signal with the sensor SA, and each of the addressed sensors SA connected to the sensor line 13 is Due to the drop in the voltage level of the sensor line 13 (the drop from the power supply VCC to the power supply VDD), the CPU mounted on each of them is driven to enter a multiplexed signal reception state.

The time T1 (approximately
25 ms) (this time T1 is
(This is provided to wait for the time until the CPU enters the operating state.) Since the control means 26 outputs a gate signal to the transmission switching circuit 27, the photocoupler 25b of the insulated transmission circuit 25 is ready for transmission. , Multiplex transmission control unit 2
The multiplexed signal (multiplexed signal having an amplitude of +24 volts and −24 volts) received by the multiplexed signal receiving circuit 22b is transmitted to the monitor signal level conversion circuit 23a through the photocoupler 25b, so that the transistor Q1 causes the multiplexed signal. ON according to the
Turned off.

This multiplexed signal is a photocoupler 25 at +24 volts.
b is turned off and turned on at −24 volts, so that the transistor Q1 is turned off when the multiplexed signal is at +24 volts, and the power VDD supplied through the resistor R1 is changed to the Zener diode Z.
After being dropped to about 5 volts at D1, a voltage of about 5 volts is supplied to the sensor line 13 (terminal LN) through the transistor Q2 and the diode D2. Conversely, when the multiplex signal is at -24 volts, the transistor Q1 is turned on. Power supply VDD is a resistor R
1, Terminal LN through transistors Q1, Q2 and diode D2
Supply a voltage of about 12 volts. Therefore, the multiplexed signal having the amplitude of +24 or -24 volts is converted into a multiplexed signal having an amplitude of between 5 volts and 12 volts between the terminals LN and CN by the monitor signal level conversion circuit 23a. Transmitted to SA.

On the other hand, the address-attached sensor SA that has received the level-converted multiplex signal changes its internal impedance to change the current level flowing through the sensor line l3, and outputs a reply signal. The response signal level conversion circuit 24b of the level conversion control unit 23 detects the signal.

That is, when one addressable sensor SA sends a reply signal, the current flowing through the sensor line 13 fluctuates, and the power supply VD
The current level supplied from D through the resistor R1, the transistors Q1, Q2, and the diode D2 fluctuates, and a voltage corresponding to the fluctuation of the current level is generated across the resistor R1.

This voltage is applied to the amplifier AMP1 of the return signal level conversion circuit 23b.
After conversion and amplification by the current / voltage conversion circuit composed of
By applying the power supply VDD to the comparator CMP1 having a reference voltage divided by the resistors R2 and R3, when the current of the detector line l3 increases, the comparator CMP1 outputs an "H" level voltage. Is decreased, the comparator CMP1 outputs an "L" level voltage.
Here, the time T1 from the start of the transmission period of the multiplex signal
(About 25 milliseconds), the control means 26
As a result, the transmission switching circuit 27 is driven to the conductive state, and thereby the photocoupler 25b is set to the transmittable state.At this time, the photocoupler 27a is simultaneously switched to the ON state, so that the output voltage of the comparator CMP1 passes through the photocoupler 25c. Is transmitted to the multiplex signal transmission circuit 22c of the multiplex transmission control unit 22.

That is, the sensor return signal from the address-added sensor SA is level-converted by the return signal level conversion circuit 23b and transmitted to the multiplex signal line 1.

When the transmission and reception of the fire information by the multiplex signal between the fire receiver 1 and each of the sensors SA via the repeater 2 is completed, the fire receiver 1 sends a transmission switching end signal to the repeater 2. Then, the control means 26 of the repeater 2 determines the end of the transmission / reception of the multiplex signal, switches the photocouplers 25a and 27a to the off state, and interrupts the signal transmission of the photocoupler 25b.

This turns off transistor Q3 and turns off transistor
Since Q4 is turned on, transistors Q5 and Q6 are turned on at the same time, power supply VCC and power supply VEE are supplied to terminal LN, and detector line l3 has the voltage level of power supply VCC and returns to the original monitoring state voltage level. I do.

Finally, the operation of the general sensor monitoring period in which the alarm signal of the general sensor S having no address is transmitted to the fire receiver 1 via the repeater 2 will be described.

Repeater 2 from fire receiver 1 via multiplex signal line 1
When a monitoring start signal with an address is input, the multiplexed signal is decoded by the control means 26 via the multiplex transmission control unit 22, and the control means 26 reads the output voltage level of the level determination unit 28 and issues an alarm. Determine the situation.

Here, when the general sensor S does not issue an alarm, the terminal LN connected to the sensor line l3 is at the voltage level of the power supply VCC. However, when the sensor S issues an alarm, the sensor line l3 switches to the sensor S3. Shorted through the internal resistance of the

However, due to the current limiting circuit 24a including the transistor Q5, the resistor R8 connected to the emitter thereof, and the diodes D6 and D7 connected to the base, the voltage drop of the resistor R8 causes the forward voltage of the diode D6 (or D7) to decrease. If it exceeds (approximately 0.6 volts), the current limit is applied and the output current of the transistor Q5 is limited. When the general sensor S issues an alarm, the output voltage level of the current limit circuit 24a falls below the level of the power supply VEE. As a result, the diode D1 conducts, and power is supplied to the detector line 13 from the power supply VEE having a low internal impedance.

On the other hand, the comparator CMP2 of the level determination circuit 28a has the reference voltage 28b of the level ER (about 19 volts) obtained by dividing the power supply VCC by the resistors R4 and R5. When the voltage level of the sensor line l3 is VCC, the alarm monitor signal of the "H" level is output. However, when the detector S issues an alarm, the voltage level of the sensor line l3 drops and becomes lower than the reference voltage ER. Therefore, an "L" level general sensor determination signal is output.

Therefore, the control unit 26 determines the alert of the general sensor S from the level of the general sensor determination signal, and transmits the alert determination signal to the fire receiver 1 side. A fire alarm is output according to the discrimination signal. This general sensor monitoring period is terminated when the repeater 2 returns a notification discrimination signal.

[Effects of the Invention] As can be understood from the above description, according to the method of the present invention, a monitoring signal with a detector address is transmitted and received between a fire receiver and a detector connected to a detector line. The relay can be easily applied to a fire monitoring system using multiplex transmission in which a multiplex signal transmitted and received between the two is simply level-converted, and a sensor disconnection can be easily detected.

Further, according to the system of the present invention, it is possible to provide a system in which a disconnection detection function of a sensing line is added to a fire monitoring system using a multiplex transmission system in which the function of a repeater is simplified and the total cost is reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a fire monitoring system according to the present invention.
FIG. 3 is a time chart showing signal transmission with an addressed sensor, FIG. 3 is a block diagram of an internal circuit of the repeater, FIG.
Fig. 5 is a circuit diagram of the terminator, Fig. 5 is a time chart for explaining its operation, Figs. 6a and 6b are explanatory diagrams of the principle of the continuity test method of the present invention, and Fig. 6a is when the sensor line is normal. 6b is an operation explanatory diagram at the time of disconnection, FIG. 7 is a circuit diagram of a main part inside the repeater, FIG. 8 is a time chart explaining the operation of each part at the time of the continuity test of the present invention, FIG. FIG. 9 shows a basic configuration diagram of a conventional fire monitoring system. (Explanation of symbols) 1 ... Fire receiver 11 ... Multiplex transmission control unit 12 ... Control means 13 ... Alarm means 14 ... Sensor power supply 2 ... Repeater 21 ... Address setting unit 22 ... Multiplex transmission Control unit 23 Level conversion control unit 24 Continuity test means 24a Current limiting circuit 24b Constant voltage power supply circuit 24c Switching circuit 25 Insulated transmission circuit 26 Control means 27 Transmission switching circuit 28 Level detector 4 Terminator 1 Multiple signal line l2 Detector power supply line l3 Detector line Vcc Level for monitoring the detector VDD Level for not operating the terminator T1S ... First monitoring timing T2S... Second monitoring timing SA... Sensor with address S... General sensor without address

Claims (3)

(57) [Claims] 1. A fire receiver and a plurality of repeaters are connected by a multiplex signal line, and at least a plurality of detectors to which addresses are assigned are connected to these repeaters. Further, a terminator is connected to the end of these sensor lines so that, when a voltage higher than a predetermined level is supplied, the current supplied to the sensor line is continuously absorbed for a predetermined time. A fire monitoring system using multiplex transmission, wherein power is supplied to the detector line from the detector power supply of the fire receiver side through the detector power supply line, wherein the fire receiver side is connected to the relay side. Transmits a transmission switching signal of a specific multiplex transmission level specifying a repeater address via a multiplex signal line by a polling method, and the relay receiving the transmission switching signal transmits the transmission switching signal to the switching signal. The monitor signal specified by the sensor address transmitted from the fire receiver side via the multiplex signal line is converted to a level corresponding to the sensor line, and sent out to the sensor line as it is. A fire monitoring system configured to perform a basic operation of converting a return signal returned from the sensor with an address to the detector line to a specific multiplex signal level again at the repeater side and returning it to the fire receiver side , A continuity test start signal specifying a repeater address is transmitted from the fire receiver side to the repeater side via a multiplexed signal line by a polling method, and the repeater side receiving the continuity test start signal transmits After the voltage level supplied from the sensor line to the sensor side is reduced from a normal sensor monitoring level to a level at which the terminator is not operated for a predetermined time, the sensor monitoring is performed. While returning to the visual level, the terminator is supplied with the voltage of the inoperable level of the terminator to the sensor line, and the terminator is started after the supply of the voltage at the sensor monitoring level to the sensor line is started. A voltage level occurring in the sensor line is detected during each of the periods until the current sink operation is completed, and the detected voltage level is lower than a predetermined reference level at the first monitoring timing, and the next monitoring timing In the case where it becomes higher than the predetermined reference level, the detector line is determined to be disconnected, a disconnection detection signal is returned to the fire receiver side, and the fire receiver side receiving the disconnection detection signal A similar continuity test start signal is sent to the repeater side, and in the same manner, when the fire receiver side receives a predetermined number of disconnection detection signals from the repeater side, the fire receiver side Multiplexing fire breaking detection method of monitoring system in sensor lines utilizing, characterized in that the generating a warning signal for informing the disconnection of the sensor lines. 2. A fire receiver and a plurality of repeaters are connected by a multiplex signal line, and at least a plurality of detectors to which addresses are assigned are connected to these repeaters. To the ends of these sensor lines, a terminator is connected to perform continuous operation of sucking the current supplied to the sensor lines for a predetermined time when a voltage of a predetermined level or more is supplied, and Power is supplied from the detector power supply on the fire receiver side to the relay line via the detector power supply line, and relaying is performed from the fire receiver side to the repeater side via a multiplex signal line by a polling method. A transmission switching signal of a specific level, which specifies a device address, is transmitted. On the repeater side receiving the transmission switching signal, the sensing signal transmitted from the fire receiver side via a multiplex signal line following the switching signal is detected. The specified monitoring signal of the address,
The signal is converted to the level corresponding to the sensor line, sent out to the sensor line as it is, and the reply signal returned from the address-equipped sensor receiving the monitor signal to the sensor line is returned to the repeater side at the specific multiplex transmission level. In the fire monitoring system configured to perform a basic operation of converting to the fire receiver side and returning to the fire receiver side, the fire receiver is connected to a sensor line and a sensor line derived from a repeater in the system. Monitor the sensor and output an alarm signal at least when the sensor is activated and when the disconnection of the sensor line is determined. For this purpose, each repeater in the system is connected via a multiplex signal line. To monitor the sensor lines of these repeaters, send a continuity test start signal to the multiplex signal line, and receive a disconnection detection signal returned from the repeater. A multiplex transmission control unit for operating the multiplex transmission control unit according to a preset control program, and decodes the multiplex signal including the disconnection detection signal received by the multiplex transmission control unit to perform necessary processing. Control means, and at least a sensor power supply connected to each of the repeaters in the system via a sensor power supply line to supply power of a level required for the alarming operation of the sensor, A multiplex transmission control unit for receiving a continuity test start signal transmitted from the fire receiver via a multiplex signal line and returning a disconnection detection signal to the fire receiver; An address setting unit for setting an address to be added to the multiplexed signal to be transmitted; and a detector line supplied with power from a detector power supply of the fire receiver through a detector power supply line. The multiplex transmission control unit is activated when the continuity test start signal is received from the fire receiver, and changes the voltage level supplied to the sensor line for a predetermined time to the terminal connected to the sensor line. Continuity test means for lowering the voltage to be supplied to the sensor line to a normal monitoring level after a predetermined time has elapsed, and a continuity test means for lowering the voltage to be supplied to the sensor line after a predetermined period of time. The voltage level to be supplied is reduced to a non-operation level of a terminator connected to the sensor line for a predetermined period of time, and when the voltage level is restored to a normal monitoring level after the lapse of the time, two times. In the period, the voltage level occurring in the sensor line is taken out, and the voltage level taken out is compared with a predetermined reference level. Control means for determining whether there is a disconnection in the sensor line based on a determination signal by the level determination means and sending a determination signal to the multiplex transmission control unit in order to return a test signal including a line detection signal. A fire monitoring system using multiplex transmission. 3. The continuity test means is interposed between the sensor power supply line and the sensor line, and is normally a voltage from the sensor power supply line to the sensor line side for the alarm operation of the sensor. While the supply is permitted, a voltage adjustment circuit that supplies a constant voltage that is lower by a certain level than during normal monitoring to the sensor line when the sensor line is alerted, and a multiplex signal sent from the fire receiver side 3. A switching circuit for interrupting a supply operation of the voltage adjustment circuit to a sensor line for a predetermined time when a voltage interruption signal is received from the decrypted control means. 2. A fire monitoring system using multiplex transmission according to 2.