EP0042501B1 - 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 device for transmitting measured values in a fire alarm system of the type defined in the preamble of claim 1.

Automatic fire alarm systems have the task of detecting fires as early as possible in order to enable effective fighting. A requirement that is set in the fire detector 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, instead of an alarm signal, to transmit the measured value analogous to the fire parameter to be measured to the signaling center and to have the decision 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.

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

In recent years, several fire alarm systems have been developed that can be used to identify detectors and transmit measured values to the control center. However, the complexity of the circuitry is very 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.

In order to overcome this disadvantage, DE-AS 2 533 382 proposed a method for transmitting measured values in a fire detection system, in which the measured values determined by individual fire detectors lying in a chain on the detection lines are passed analogously to a signaling center and there for obtaining differentiated malfunctions. or alarm messages are linked, with all fire detectors being separated from the detection line by a voltage change at the beginning of each query cycle and then being switched on again in a predetermined order in such a way that each fire detector also connects the subsequent fire detectors to the line voltage after a time delay corresponding to its measured value switches 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.

Firstly, the installation of the serial detector must incur increased effort 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 installation technology of two-wire systems, this means an aggravation and also a source of errors.

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 device for transmitting measured values in a fire alarm system, which avoid the disadvantages mentioned above, d. H. enable the transmission of measured values even if a fire detector in a detection line fails 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 does not are exchanged and which ultimately allow a higher current to be sent through the detection lines or a larger number of fire detectors to be connected to the detection line.

This object is achieved by the features defined in the characterizing part of claim 1. Preferred embodiments of the invention or special embodiments of the invention defined in claim 1 are described in further claims.

The device according to the invention is preferably used in a method for transmitting measured values in a fire alarm system in such a way that, after the measured value of the last detector of a line has been transmitted, current is fed into the detection lines from both sides. By connecting the detection lines on both sides, the current serving to supply the fire detectors can be practically quadrupled.

It can also be done in such a way that the measurement 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 a detector is switched on, ie when the connection to the control center is established, this is followed by the conversion of the measured value into a coded pulse sequence or an alternating voltage signal whose frequency is dependent on the measured value. It goes without saying that the duration of the measured value signal must be shorter than the delay time.

From FR-A-2 176004 a transmission system has become known in which local transmission stations for the transmission of messages via a first line loop in series and for monitoring via a second line loop are connected in parallel to a central station. Messages from the local transmission stations are transmitted via the first line loop, for example by means of direct current pulses. The central station transmits alternating current pulses via the second line loop at certain time intervals, which actuate electronic switching devices in the local transmission stations and initiate the transmission of a message via the first line loop when the switching device reaches the switching position assigned to the individual transmission station. All transmission stations receive the monitoring impulses at the same time, they have no bidirectional switching elements and, above all, no equivalent inputs that make installation easier. In addition, the transmission system of FR-A-2 176 004 requires an increased outlay on lines.

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

• Fig. 1 eine Ausführungsform einer erfindungsgemäßen Einrichtung für ein Brandmeldesystem,
• 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.

It shows

• 1 shows an embodiment of a device according to the invention for a fire alarm system,
• 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 Li ... Li emanate from terminals K _1a ... K _ia from a signal center Z.

Several M ₁₁ ... M _1m fire detectors are connected to each of these lines. The fire detectors M ₁₁ ... M _1m essentially contain, in addition to sensors sensitive to fire parameters, a transducer, a timer, and a bidirectional switch S. From the last fire detector of a detection line, two lines are connected to the terminals K) x ... K; x of the signaling center Z returned. 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 switches of the detectors in a zone close in succession. 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; _{a 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 terminals K _{ix of} the relevant detector lines. The fire detectors are now interrogated in the opposite direction to the faulty location.

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

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

A smoke-sensitive measuring ionization 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 D13 and D14 are used for balancing, i. h, 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 1A / 1B and 2 or 1A / 1B and 3, transistor T19 initially remains blocked. At the same time, the timer T starts and, after a time delay which is given by the value of the voltage U _A , opens the transistor T19 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 measurement ionization chamber serves as an example as a smoke-sensitive sensor.

The measurement ionization chamber MK is connected in series with a comparison resistor R _2, in its place a reference ionization chamber can also be used, to the stabilized voltage U _s . The capacitor C20 is charged via the rectifier D11 and bridges the systemic periodic interruptions in the line voltage. The transistor T16 forms, together with the resistor R and the zener diode D12, a voltage stabilization U _s in a known manner. The MOSFET T18 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 R4, R5 and R6. The output voltage U _{A of} the operational amplifier is proportional to the sensor voltage U _K.

In the normal operating state, the transistor T17 is not conductive, the gate connection of the bidirectional switch T19 is therefore at the potential of the connection 1, as a result of which the transistor T19 is kept conductive. The voltage across the capacitor C21 is approximately limited by the diode 15 to the value of the amplifier output voltage U _A. Now, when the line voltage is lowered to zero at the beginning of an interrogation cycle, the capacitor C21 discharges to zero via the resistors R7, R9 and R10. When the line voltage is switched on again, a charging current flows through the resistor R7 to the capacitor C21 and further via the resistor R10. The transistor T17 thus becomes conductive and an additional current flows through the resistor R8. The gate potential of T19 jumps below the threshold voltage of the field effect transistor and thus blocks T19. If the capacitor C21 has now charged up to the output voltage U _{A of} the amplifier via the resistor R7, no further charging current flows to C21, which means that T17 blocks. The gate of T19 jumps back to the potential of connection 1 and thus brings switch T19 into the conductive state.

The diodes D13 and D14 ensure a symmetrical supply to the detector electronics, which, together with the symmetry properties of the transistor T19, 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 T19 are conceivable. JFETs or relays can also be used as bidirectional switches.

4 shows an embodiment of the method according to the invention in which the time delay is independent of the measured value. The mode of operation is similar to that shown in FIG. 2. However, the output voltage U _{A of} the 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 use is made to the control center, the measured value is converted into a coded pulse train 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 T19 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 transmission of measured values and the addressing of the detector.

Claims (6)

1. Apparatus for a fire alarm system comprising a central signal station (Z) and a plurality of fire alarms (M11 to M1m) arranged in a chain-like fashion at alarm reporting lines (L11 to L1m) which alarm reporting lines (L11 to L1m) are returned from the last fire alarm (M1 m, Mim) to the central station (Z) in which apparatus each individual fire alarm (M) within an interrogation cycle its measuring values transmits to the central signal station (Z) and all fire alarms (M) at the start of one of each interrogation cycle are disconnected from the central signal station (Z) by a voltage change of the alarm reporting line (L) and then all fire alarms (M) are reconnected in a timewise staggered fashion such that each fire alarm (M) after a certain time-delay additionally connects a subsequently arrannged fire alarm with the line voltage and each reconnected fire alarm (M) reports its address and wherein upon absence of measuring signals the interrogation direction for the affected alarm reporting line (L) is reversed, characterized in that each fire alarm (M1m to Mim) comprises two equivalent terminals (1A, 1B, 2; 1A, 1B, 3) for connecting it with the alarm reporting lines (L1 to Li) and a bidirectional switch (T19) for connecting the next (in the direction of interrogation) fire alarm in the chain with the alarm reporting lines.

2. Apparatus according to claim 1, characterized in that each fire alarm (M) comprises an electrical circuit (T, R7, R8, R10, C21, T17) which upon application of a potential at one of both inputs (1A, 1B, 2; 1A, 1B, 3) after a time-delay causes the bidirectional switch (T19) to generate a signal at the other input (3; 2) (Figures 2, 3, 4).

3. Apparatus according to claim 2, characterized in that the circuit and the bidirectional switch (T19) are connected with each other by diodes (D13, D14) (Figures 2, 3, 4).

4. Apparatus according to claim 2, characterized in that the time delay is dependent upon the measuring value (UA) of the sensors (MK, MW) (Figures 2, 3).

5. Apparatus according to claim 2, characterized in that the time delay is independent upon the measuring value (UA) of the sensors (MK, MW) and that the measuring value (UA) is transmitted to the central signal station (Z) within the time delay (Figure 4).

6. Apparatus according to claim 1, characterized in that the bidirectional switch (T19) is a relay, a MOS-FET transistor or a JFET transistor.

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