EP0042501A1 - Device for the transmission of measured values in a fire warning system - Google Patents

Abstract

In a fire alarm system individual fire alarms are connected in series by reporting lines with a central signal station. In order to be able to connect a greater number of fire alarms with the individual reporting or signaling lines and/or in order to be able to dispatch an increased amount of current through the reporting lines, the reporting or signaling lines from the last fire alarm of a line are returned back to the central signal station in the form of a ring circuit or loop. Upon the absence of signals at a reporting line an interrogation device is reversed, so that there can be ensured that in the event of a line disturbance or breakdown of a fire alarm the remainder of the fire alarms still can be utilized for giving a signal. The individual fire alarms are structured such that during assembly the inputs and outputs can be mutually interchanged.

Description

The invention relates to a method for the transmission of _M esswerten in a fire alarm system, said fire detectors form of a chain of individual lying on signal lines given determined measurement values to a central signal station and linked there to obtain differentiated fault or alarm messages.

Automatic fire alarm systems have the task of detecting fires as early as possible in order to enable effective fighting. A requirement that is placed on fire detectors is high sensitivity in order to use traces of fire by-products for fire detection. Unfortunately, in parallel with the increase in sensitivity, there is also a tendency towards false alarms. In the signaling center, it is therefore sometimes difficult to distinguish between a real alarm and a false alarm.

To overcome this disadvantage, it has already been proposed to transmit the measured value analogous to the fire parameter to be measured to the signaling center instead of an alarm signal and to have the decision made as to whether it is a fire or a fault in the signaling center, because from the comparison of the Measured variables of different detectors a much more accurate statement can be made.

However, a prerequisite for a meaningful evaluation of the detector signals in the signal center is that the origin of the signals can be clearly determined, i.e. the detectors must be identifiable, i.e. be addressable.

In recent years, several fire alarm systems have been developed in which a detector identification is possible and a Messwertü _b ertractunq taking place at the headquarters. However, the circuitry is very complex high or the installation is associated with application-related difficulties.

The main disadvantage of these methods is that each detector must be set individually to determine the detector address. This results in dangers of incorrect addressing and the associated incorrect identification.

To overcome this disadvantage, DE-AS 2'533'382 proposed a method for transmitting measured values in a fire alarm system, in which the measured values determined by individual fire detectors lying in chains on the detection lines are passed analogously to a signaling center and differentiated there for gain Fault or alarm messages are linked, with all fire detectors being disconnected from the detection line by a voltage change at the beginning of each query cycle and then switched on again in a predetermined order in such a way that each fire detector additionally switches on the subsequent fire detector after a time delay corresponding to its measured value the line voltage is switched on and that in the signaling center the respective detector address is derived from the number of previous increases in the line current and the measured value from the length of the switching delay in question.

However, this method also has three basic disadvantages.

First, the installation of the serial detector has to be more expensive to ensure that the detectors are connected correctly. Even if one speaks of a two-wire system, the detector still has three terminals and you have to make sure that the incoming and outgoing wire are not interchanged. Compared to the classic In installation technology of two-wire systems an aggravation and also a source of error.

Second, the number of detectors per line is limited by the resistance of the switches connected in series.

Third, if a detector fails or the line is interrupted or short-circuited, at least some of the detectors on a line are deactivated.

The object of the invention is to provide a method of transmitting measured values in a fire alarm system and a device for implementing the method which avoid the aforementioned disadvantages, the transmission means of measured values also allow when a _B edge detector fails in a signal line or a detector line is interrupted or short-circuited, which also allows the fire detectors to be connected to the detection lines without having to take care that the entry and exit of the detection line are not interchanged and which ultimately allow a higher current to be sent through the detection lines or to connect a larger number of fire detectors to the detection line.

According to the invention, this is achieved in that the detection lines are returned from the last fire detector of a line to the signaling center and that, in the absence of detector signals, the interrogation direction for the affected detection line is reversed. This ensures that in the event of a lead accident or failure of a detector, the rest of the fire detectors in this detection line can still be used to signal.

According to a preferred embodiment of the method according to the invention, after the measurement value of the last detector of a line has been transmitted, current is fed into the detection lines from both sides. The two-sided connection of the detection lines ensures that the electricity used to power the fire detectors can be practically quadrupled.

According to another embodiment of the method according to the invention, the measured values are transmitted in the delay time between two detector connections, the time delay is not dependent on the measured value and remains constant.

Immediately after switching on a detector, i.e. When the connection to the control center is established, the measured value is converted into a coded pulse train or an AC signal whose frequency depends on the measured value. It goes without saying that the duration of the measured value signal must be shorter than the delay time.

A device for carrying out the method according to the invention consists of a sensor which is sensitive to fire parameters, a transducer, a timer and a bidirectional switch which switches the next fire detector to the detection line.

Preferred embodiments of the invention are explained in more detail below with reference to the drawings.

• Fig. 1 eine Ausführungsform eines Brandmeldesystems zur Durchführung des erfindungsgemässen Verfahrens.
• Fig. 2 eine Schaltungsanordnung für einen Brandmelder, bei dem die Zeitverzögerung vom Messwert abhängig ist.
• Fig. 3 eine bevorzugte Ausführungsform der Schaltungsanordnung gemäss Fig. 2 .
• Fig. 4 eine Schaltungsanordnung für einen Brandmelder dessen Zeitverzögerung vom Messwert unabhängig ist.

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• Fig. 1 shows an embodiment of a fire detection system for performing the method according to the invention.
• Fig. 2 shows a circuit arrangement for a fire detector in which the time delay is dependent on the measured value.
• 3 shows a preferred embodiment of the circuit arrangement according to FIG. 2.
• Fig. 4 shows a circuit arrangement for a fire detector whose time delay is independent of the measured value.

1 shows the structure of a fire alarm system for the transmission method according to the invention. Signaling lines L ₁ ... Li emanate from the signaling center Z from the terminals K _la ... K _ia .

Several M ₁₁ ... M _1m fire detectors are connected to each of these lines. In addition to sensors sensitive to fire _parameters , the M ₁₁ ... M _1m fire detectors essentially contain a measured value converter, a timer and a bidirectional switch S. From the last fire detector of a detection line, two lines are fed back to the terminals K _lx ... K _{ix of} the signal center Z. . After applying the line voltage to the terminals K _1a , a timer starts to run in the M ₁₁ detector. After a certain delay, the switch S ₁₁ closes and applies the line voltage to the detector M _{12 ',} where a timer also starts to run again. In this way, all the switches of the detectors in a zone close one after the other. This process can be repeated periodically so that the fire detectors of a detection line are polled cyclically. After the line voltage has been applied to a detector or the relevant switch has been closed, the measured values from the sensor can be transmitted to the signaling center.

At the end of a query cycle, storage capacitors in the detectors are charged, which ensure the energy supply to the fire detectors during system-related interruptions.

In normal operation, ie in the undisturbed state, the detector line evaluation circuit of the signal center Z is connected to the terminals K _{ia of} the lines concerned.

The occurrence of a line fault or the failure of a detector is detected in the signal center Z by the fact that the polling cycle stops. In this case, the detector line evaluation circuit is automatically switched to the Kix terminals of the relevant detector lines. The fire detectors are now interrogated in the opposite direction to the disturbed point.

By periodically switching the detector line evaluation circuit from the terminals K _ia to the terminals K _ix it is achieved that even in the event of a fault, the still intact detectors of a detector line can transmit their measured values to the signal center Z.

2 shows the circuit arrangement of a fire detector M, in which the time delay is controlled by the measured value.

A smoke-sensitive mession chamber MK is drawn as the sensor, the current of which generates the voltage U _K at the external resistor R ₂ . This voltage is fed to the input of the transducer MW, the output voltage U _A of which acts on the timing element T. The bidirectional switch 19 is used to switch the line voltage to the next detector. The diodes D 13 and D 14 are used for balancing, ie when installing the fire detector, it is not necessary to pay attention to the correct sequence of connections 2 and 3.

When the line voltage is applied to terminals IA / IB and 2 or IA / IB and 3, transistor T 19 initially remains blocked. At the same time, the timer T starts and opens the transistor T 19 after a time delay which is given by the value of the voltage U _A and thus switches the line voltage to the next detector.

When the line voltage is applied, a resistor in the fire detector is also switched on, which causes the current increase, which is evaluated in the control center to determine the detector address.

FIG. 3 shows a circuit arrangement of a preferred embodiment of a fire detector according to FIG. 2. A fire detector with a mession chamber serves as an example as a smoke-sensitive sensor.

The mession chamber MK is connected in series with a comparison resistor R _2, in its place a reference ionization chamber can also be used, to which stabilized voltage U _{s is} connected. The capacitor C 20 is charged via the rectifier D 11 and bridges the systemic periodic interruptions in the line voltage. The transistor T 16 together with the resistor R ₁ and the Zener diode D 12 forms a voltage stabilization U _s in a known manner. The MOSFET T 18 serves as an impedance converter, ie it transmits the output voltage U _{K of} the sensor to the input of the operational amplifier A, the operating point of which is determined by the resistors R 4, R 5 and R 6. The output voltage U _{A of} the operational amplifier is proportional to the sensor voltage _UK .

In the normal operating state, the transistor T 17 is not conductive, the gate connection of the bidirectional switch T 19 is therefore at the potential of the connection 1, as a result of which the transistor T 19 is kept conductive. The voltage across the capacitor C 21 is approximately limited by the diode 15 to the value of the amplifier output voltage U _A. If the line voltage is now reduced to zero at the beginning of an interrogation cycle, the capacitor C 21 discharges to zero via the resistors R 7, R 9 and R 10. When the line voltage is switched on again, a charging current flows through the resistor R 7 to the capacitor C 21 and further via the resistor R 10. Thus the transistor T 17 becomes conductive and an additional current flows through the resistor R 8. The gate potential of T 19 jumps below the threshold voltage of the field effect transistor and thus blocks T 19. If the capacitor C 21 has now charged up to the output voltage U _{A of} the amplifier via the resistor R 7, no further charging current flows to C 21, which means that T 17 locks. The gate of T 19 jumps back to the potential of connection 1 and brings switch T 19 into the conductive state Status.

The diodes D 13 and D 14 ensure a symmetrical supply of the detector electronics, which, together with the symmetry properties of the transistor T 19, enables the optional supply from connection 2 or connection 3. In a similar way, circuit arrangements with other symmetrical switching elements instead of the transistor T 19 are conceivable. JFETs or relays can also be used as bidirectional switches.

In FIG. 4, an embodiment of the inventive method is shown in which the time delay from _M is independently esswert. The mode of operation is similar to that shown in FIG. 2. However, the output voltage U _{A of} the measuring transducer MW does not control the timing element T. Immediately after the line voltage has been applied to terminals 2 or 3, i.e. when the connection to the control center has been established, the measured value is converted into a coded pulse sequence or an AC signal, the frequency of which is determined by the measured value. This signal is received at the control center and evaluated accordingly. At the same time, the timer T runs and switches on the transistor T 19 after a fixed preselected time and thus switches the line voltage on to the next detector. It goes without saying that the duration of the measured value signal must be shorter than the switch-on delay. This embodiment has the advantage that it is possible to separate between the measured value transmission and the detector addressing.

Claims (10)

1. A method of transmitting measured values in a fire alarm system, wherein the individual chain form of message _- lines lying fire detectors determined measured values are supplied to a signal center and linked there to obtain differentiated fault or alarm messages, and wherein the beginning of each interrogation cycle all detectors by a voltage change in the detection line is disconnected and then switched on again in a staggered manner in such a way that, after a certain time delay, each detector additionally connects a subsequent detector to the line voltage, and in the evaluation device the respective detector address is derived from the number of previous increases in the line current, characterized in that the detection lines (L ₁ ... L _i ) from the last fire detector (M _lm ... M _im ) are fed back to terminals (K _lx ... K _ix ) of the signaling center (Z) and that if Detector signals the query direction for the affected detector is never reversed. 2. The method according to claim 1, characterized in that after the transmission of the measured value of the last detector of a line, both the terminals (K _ia ) and the terminals (K _ix ) feed current into the detection lines. 3. The method according to claim 1 or 2, characterized in that the time delay is determined by the measured value of the detectors. 4. The method according to claim 1 or 2 characterized in that the time delay of the measured value is independent and that the _M esswert within the time delay for the signal center is passed. 5. The method according to claim 4, characterized in that the measured value is forwarded to the signal center in the form of a coded pulse sequence. 6. The method according to claim 4, characterized in that the measured value is transmitted in the form of an AC voltage signal with a frequency dependent on the measured value. 7. Device for performing the method according to claim 1, characterized in that the individual fire detectors (M) have two inputs for connection to the detection lines (L ₁ ... L _i ), and circuit elements which, when voltage is applied to one of the two Delayed inputs generate a signal at the other input and vice versa. 8. Device according to claim 7, characterized in that one of the circuit elements is a bidirectional switch (T 19). 9. Device according to claim 8, characterized in that the bidirectional switch (T 19) is a relay, a MOSFET or a JFET. 10. Device according to claim 7, characterized in that the connection of the circuit elements to the connections of the bidirectional switch via diodes (D 13) and (D 14).

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