EP2428942B1 - Hazard notification assembly with two data transfer speeds - Google Patents

Description

The invention relates to a hazard detection system with a center to which the beginning and the end of a two-wire fieldbus for power supply to and for bidirectional communication with participants is connected, which are spatially spaced and electrically parallel between the wires of the fieldbus. The invention further relates to a method for operating such a hazard alarm system after the occurrence of a fault in the course of the field bus or in one of the connected participants.

In the case of larger, hierarchically structured alarm systems, the control center can also be a sub-center or a coupler. To increase the reliability, the fieldbus, which can have a length of considerably more than 1 km, is returned in a ring shape to the control center. The subscribers connected to the fieldbus can be sensors, eg fire or intrusion detectors as well as actuators, eg warning lights. In normal operation, the power supply and communication of the field bus or connected to this participant via the beginning of the field bus, which has at its returned to the center end a terminator, for example in the form of a resistor or an active module, which is a test of the two-wire line in particular to short circuit or interruption.

Both states can occur abruptly or insidiously and are referred to below as errors for short. Methods are known which locate and isolate the fault location in such an error case. For this purpose, the fieldbus is performed in each participant via two switchable, in series line disconnector, which opens the center in case of an error in the field bus or a subscriber first and then, starting from both the beginning and the end of the field bus, one after the other to the each last participant on both sides of the fault closes again. If the fault is a short circuit, however, at least the line disconnectors located on the side of the fault location of the respectively last station remain open. Subsequently, the fieldbus is no longer operated in the ring but in the form of two stubs from the physical beginning and from the physical end to the fault location and the danger monitoring continues.

On this side, a hazard detection system has been developed in which participants such as video cameras, microphones and loudspeakers, which require a high data transmission rate, can also be connected to the fieldbus. Therefore, the center communicates with these subscribers at a second data rate higher than a first data rate for the optionally prioritized communication between the center and e.g. to the detectors. The data may be sent from the central office to the subscribers e.g. be transmitted by AMI or NRZ voltage modulation and in the reverse direction by corresponding current modulation.

The following is the first data transfer rate as low speed mode (LS operation) and the corresponding Subscriber as LS subscriber, the second, higher data transfer rate than High Speed Mode (HS mode) and the corresponding subscribers as HS subscribers.

In the above-mentioned error case, the control unit switches off the terminator in order to be able to operate the field bus also from its end. Without a terminator, reliable communication with the subscribers via the spurs is no longer guaranteed, at least in HS operation, because the reflections of the signals can affect the signals and data packets received and transmitted by the subscribers to such an extent that correct decoding is no longer possible ,

EP 0 581 248 A1 and US 5 097 259 A show danger warning systems according to the preamble of claim 1.

The invention is therefore an object of the invention to provide a hazard alarm system, in which a secure communication between the center and at least some of the remaining functional participants is guaranteed even in case of failure.

According to the invention this object is achieved by the hazard detection system according to claim 1 and by the method according to claim 11. The subclaims relate to further advantageous embodiments of the invention.

This object is inventively achieved in that at least some of the participants between the two wires of the fieldbus have at least one switchable RC-terminator, which is turned off in normal operation and can be switched on in the event of a fault. As a result, the fieldbus is only charged with AC voltage, i. in the terminator, a current flow occurs only during the signal edges

In the event of an error, the terminator of the last subscriber equipped with it is switched on at the end of the two stubs resulting from the isolation of the fault location. Since the respective last physical subscriber can be both an HS and an LS subscriber, all subscribers with such a terminator are preferably those fitted. As a result, if appropriate, the communication in LS mode can also be improved.

Suitably, the terminator is switched on and off by means of a semiconductor switch. In principle, the switching on and off is also possible by means of a switching contact of a miniature relay integrated in the respective subscriber. However, this variant is usually costly and unfavorable in terms of space requirements.

The semiconductor switch may be a bipolar transistor having a diode in antiparallel to its emitter / collector path. The diode is necessary so that the capacitor of the RC element can not only charge in time with the communication pulses but can also discharge again.

Instead, a FET can be used as the semiconductor switch. Whose parasitic or substrate diode takes over the function of the separate diode in the case of a bipolar transistor. Alternatively, a double FET (two in-line FETs) may be used.

The switching state of the terminators in the participants, the control panel after detection and localization of an error by sending a command to control the already present in each participant microprocessor, which in turn controls the switching on and off of at least one end member and the switching state of the line separator. Regardless of this, the microprocessor in the event of a fault can switch off the shut-off element connected in HS operation in each case during LS operation in order to save the energy or feed power of the power supply from the control center required for the transfer of the capacitor of the terminator.

Instead, each of the subscribers may comprise an error detection circuit which switches the terminator of the subscriber - possibly only in HS mode - as soon as it has determined that this subscriber is the last subscriber at the end of the relevant branch line of the fieldbus.
The termination member may be between the common connection point of the two line disconnectors and the other field bus wire. In this case, the two line disconnectors must be independently switchable so that after the opening of both line disconnectors triggered by a fault in the form of a short circuit, only the line disconnector facing away from the fault location, that is, closer to the control center, closes again. The opening and closing of the respective Leitungsstrenner can be done from the control center via a command.

Fig. 1a:

ein Blockschaltbild einer Zentrale mit ringförmig angeschlossenem Feldbus im normalen Betrieb,

Fig. 1b:

das gleiche Blockschaltbild im Fall eines Fehlers auf dem Feldbus,

Fig. 2 bis 7:

mehrere Varianten von Teilnehmern mit Abschlussgliedern.

Instead, each of the subscribers can have a terminating element upstream of the two line isolators and a terminating element connected downstream of the line isolators between the fieldbus wires. Each of these two closure members per participant may be configured as indicated above for a single conclusion member. The two line disconnectors can be switched together and consequently with the same command. In the event of a short circuit, they remain open so that the short circuit remains disconnected. In the event of an interruption, they also remain open, so that the terminator lying on the error side is not parallel to the central-side terminator. Alternatively, the two final members could in case of error by command from the headquarters be turned on individually, so that in an error by interruption and common closing of the line separator for the construction of the stubs only the central-side termination member is effective.
Suitably, the RC element of the end member comprises a parallel resistor for discharging the capacitor. This prevents that in case of an interruption of one of the wires of the two-wire line and the subsequent connection of the end member whose capacitor discharges, if it is charged via the bus line in the direction of the center and thereby falsifies the voltage level of the communication pulses. Regardless of the parallel resistor provides for a defined operating point of the semiconductor switch for switching on and off of the end member.
The invention will be explained with reference to several embodiments in the form of simplified circuits. It shows:

Fig. 1a:

a block diagram of a control panel with ring-connected fieldbus in normal operation,

Fig. 1b:

the same block diagram in the case of a fault on the fieldbus,

2 to 7:

several variants of participants with graduates.

FIG. 1a schematically shows a center 10, to which a two-wire fieldbus line with participants 1 to 8 is connected. Participants 1 through 8 can use sensors such as Fire detectors or video cameras and actuators such as warning lights or speakers. Such a field bus may, for example, comprise over 100 such subscribers and have a length of, for example, 2 km. The center 10 supplies the participants with their operating voltage and communicates with them via the two wires of the fieldbus. For this purpose, the field bus is connected with its beginning to the terminals A + and A- of the center 10, looped through by all participants and ring with its end to further terminals B + and B- returned to the center 10.

Each participant has in one of the wires of the field bus two serial line isolators as well as among other things a modem and a microprocessor. With low traffic subscribers, the central office communicates in a low speed mode (LS mode), with high data rate subscribers, e.g. a video camera or a loudspeaker in a high-speed mode (HS operation). In the normal operating state, the end of the field bus at the terminals B + and B- of the center 10 is completed with a terminator. In LS operation, the terminator can consist of a terminating resistor that allows a simple fieldbus test for short circuit or open circuit. Instead, the termination member may be an active end module, e.g. Also allows a test of the field bus to impermissibly high line resistance under load conditions.

To reduce the reflection of steep-flanked communication signals at the end of the field bus in HS operation, the control panel 10 switches as the final member in Fig. 1a represented RC element R1, C on or from the terminating resistor to this RC element. This improves data quality and transmission security.

FIG. 1b differs from Fig. 1a by an assumed error in the form of an interruption between the subscriber 4 and the subscriber 5. As known per se, the central unit 10 shuts off all the subscribers upon occurrence of such an error, that is both in the event of an interruption and in the event of a short circuit then builds both via the terminal A +, A- as well as the terminal B +, B- the operating voltage supply and the communication with the participants or remaining participants on the two resulting from the error stubs again serially. The LS operation with the LS subscribers is in principle also possible without a terminator. For an HS operation, at least the last HS subscribers must have a terminator before the end of each of the two stubs, which replaces the disconnected terminator in the center 10. Because the fault location is not known in advance, therefore, at least every HS subscriber must be equipped with a terminator, which in the normal operating condition accordingly Fig. 1a is ineffective, but is turned on, if this participant is the "last" participant as in Fig. 1b the participant 4 and the participant 5 is.

For participants 4 and 5 this is in Fig. 1b symbolically represented. Because between the fault location and in the direction of the central office 10 nearest HS participants LS subscribers can lie, but the spurs must be completed as close to the error, all participants, that is, the LS participants, a switchable termination member expediently. The terminator of the last subscriber before the fault location switched on in the event of a fault in HS operation can be switched off during LS operation if this causes communication improved over the fieldbus in LS operation. The switch provided in each subscriber for the terminator controls the central unit 10, which recognizes during the serial construction of each of the two stubs, which subscriber is the last subscriber before the fault location, alternatively the subscriber himself, if it comprises an error detection circuit which recognizes that this participant is the last participant in the stub line.

The FIGS. 2 to 7 show the example of a participant variants of the wiring of the participants with final members. Of the other components of the subscriber known per se, only the two line disconnectors LT1 and LT2 are the fieldbus line looped through the subscriber and the microprocessor MCU controlling the operating state of the subscriber and handling the communication with the control center also carries the LS or HS operation and if necessary detects the error case and error location shown. The line disconnectors are normally two FETs, symbolically represented as (open) switching contacts, each with a parallel diode, which represents the parasitic or substrate diode of the FET in question. In the following it is assumed that the control center with its connections A +, A- left, the fault location is to the right of the respective subscriber circuit. Functionally, however, there is no difference if the fault location is left and the B +, B- connections are to the right of the subscriber; only the line disconnectors LT1 and LT2, which are shown in the non-activated state, swap their switching states during operation.

FIG. 2 shows the basic circuit, namely the line separator LT1 and LT2, at their common connection point via a switch S a termination member in the form of a capacitor C is connected in series with a resistor R1 to the wires of the fieldbus. Depending on the data transfer rate in HS operation of, for example, 50 to 150 kbit / s, the capacitor C may have a value of eg 100 nF to 330 nF and the resistor R1 a value 100 to 180 ohms. The capacitor C is charged and discharged in the rhythm of the data pulses when the switch S is closed and consequently this subscriber is the last subscriber on a spur line. Parallel to C, R1 there is a resistor R2 for discharging the capacitor C with the switch S open. R2 is high-impedance in relation to R1, because R2 loads the fieldbus with a DC-current when the switch S is closed.

The switch S is a semiconductor switch, eg correspondingly Fig. 3 a bipolar transistor T1 whose pass or blocking state is controlled by the microprocessor MCU. The resistor R2 here also ensures that the transistor T1 has a defined operating point. Since the NPN transistor T1, when it is turned on, is conductive only in one direction, is located in opposite directions parallel to its emitter / collector path, a diode D1. As a result of the different forward voltages of the NPN transistor T1 and the diode D1, an asymmetry arises during charging and discharging of the capacitor C, which can discharge via the diode D1 only to about 0.6 to 0.7 V. Instead of the bipolar transistor T1, an N-channel MOSFET or a P-channel MOSFET can be used. The respective parasitic or substrate diode takes over the function of the diode D1. Although the substrate diode may have a lower threshold voltage in the forward direction than the diode D1, but the threshold voltage of the substrate diode is, depending on the type of MOSFET, higher than the forward voltage of the source-drain path.

Such an asymmetry avoids the execution of the semiconductor switch according to the FIGS. 3a and 3b , In FIG. 3a, two P-channel MOSFETs T2, T3 are connected in series, in FIG Fig. 3b two N-channel MOSFETs T4, T5. If the respective two MOSFETs are permeable, they conduct the current in both directions.

To activate a single end member according to the FIGS. 2, 3 . 3a and 3b must after the occurrence of the error following opening of the two line disconnectors LT1 and LT2 of the central-side disconnector LT1 close together with the closing of the semiconductor switch S again. In the case of a fault due to a short circuit, however, the second line disconnector LT2 must remain open so that the short-circuit location is separated from the fieldbus. Therefore, the two line disconnectors LT1 and LT2 must be individually switchable, either from the center 10 (s. Fig. 1a, 1b ) by command or by the subscriber himself via his microprocessor MCU.

This disadvantage avoids the subscriber circuit according to Fig. 4 , It comprises two closing elements, namely a terminating element AG1 connected upstream of the line isolator LT1 from the center and a terminating element AG2 connected downstream of the line isolator LT2. The two final members AG1 and AG2 are each dimensioned the same as the only final member in the FIGS. 2 and 3 , Analogous Fig. 3 the termination elements AG1 and AG2 are respectively turned on or off via an NPN transistor T6 or T7 with antiparallel diode D2 or D3. The microprocessor MCU controls via separate outputs the switching state of the transistors T6 and T7 via diodes D4, D5 as overvoltage protection and the usual wiring the respective base with a resistance voltage divider. Line disconnectors LT1 and LT2 can be switched together and remain open in the event of a fault. The voltage supply of the subscriber and the communication with the control center are also ensured with open line disconnectors via the respective substrate diodes of the FETs, in this case that of the line disconnector LT1. The transistors T6 and T7 can be individually controlled by the microprocessor.

If the subscribers are designed for a relatively high operating voltage, eg in the range of 40 V, then in the circuit according to Fig. 4 in the event of a short-circuit fault and open line disconnectors LT1, LT2, the breakdown voltage of the emitter-base path of the transistor on the side of the short circuit is exceeded.

For the mentioned operating voltage range, the subscriber circuits are in the Figures 5 . 6 and 7 more suitable. In contrast to FIG. 4 serve as switches for the termination members AG 1 and AG 2 here PNP transistors T8 and T9.

In the embodiments according to the Figures 5 and 6 These switching transistors are connected via NPN transistors T10 and T11, which deliver a constant base current for T8 and T9 in the on state. In the blocking state, the respective base-emitter resistors of T8 and T9 hold their bases to emitter potential even in the event of a short circuit.

When switching in FIG. 5 For example, the NPN transistors T10 and T11 are controlled via separate outputs of the microprocessor MCU.

The circuit in FIG. 6 is different from the one in FIG. 5 only in that the NPN transistors T10, T11 are controlled via a common output of the microprocessor MCU. Because thus the termination elements AG1 and AG2 are turned on together, the line disconnectors LT1 and LT2 must be opened in case of an error by interruption, so that only one termination element, here the termination element AG1, becomes effective. As in the previous circuits, the command to open the line disconnectors LT1, LT2 may be generated by the central office or by the subscriber himself (if his microprocessor MCU is set up for this). In the event of an error due to a short circuit, however, a parallel connection of the closing elements AG1 and AG2 can not occur because the line isolators LT1 and LT2 remain open in any case.

The circuit according to FIG. 6 can in the in FIG. 7 illustrated manner be simplified. The PNP transistors T8 and T9 are controlled in this embodiment by the microprocessor MCU via a common NPN transistor T12.

Claims (10)

1. Alarm system comprising
   a central station (10),
   a two-wire field bus of which the start and the end are connected to the central station (10),
   a plurality of subscribers (1 to 8) that are connected to the central station (10) via the field bus for power supply and bidirectional communication,
   wherein the subscribers (1 to 8) have two switchable line separators (LT1, LT2) which are arranged in series in one wire of the field bus and through each of which the field bus is looped;
   wherein the plurality of subscribers includes at least one first subscriber and at least one second subscriber, wherein the at least one first subscriber is designed to communicate with the central station in a low-speed mode at a low data-transmission speed, and wherein the at least one second subscriber is designed to communicate with the central station in a high-speed mode at a high data-transmission speed, wherein the data-transmission speed in the high-speed mode is 50 kbit/s or more;
   wherein the alarm system is configured such that, in the event of a fault, short-circuit or disruption in the region of the field bus or a subscriber, the central station initially opens the line separators (LT1, LT2) and subsequently, beginning at both the start and the end of the field bus, closes said separators again, one after the other as far as the final subscribers (4, 5) in each case on either side of the fault location,
   wherein
   at least some of the subscribers also have a switchable RC terminal element (R1, C; AG1, AG2) provided between the two wires of the field bus;
   wherein the alarm system is configured to switch the RC terminal element (R1, C; AG1, AG2) off during normal operation and to switch it on in the event of a fault;
   and wherein the RC terminal element (R1, C; AG1, AG2) in the form of a capacitor (C) in series with a resistor (R1) is connected to the wires of the field bus.
2. Alarm system according to claim 1, wherein, in the event of a fault, the alarm system is configured to switch on the RC terminal element (R1, C; AG1, AG2) of the final subscriber (4, 5) in each case on either side of the fault location.
3. Alarm system according to either claim 1 or claim 2, comprising a semiconductor switch (S) arranged in order to switch the terminal element (AG1, AG2) on and off.
4. Alarm system according to claim 3, wherein the semiconductor switch is a bipolar transistor (T1) comprising a diode (D1) that is antiparallel to the emitter/collector path of said transistor.
5. Alarm system according to claim 3, characterised in that the semiconductor switch (S) is an FET.
6. Alarm system according to any of claims 1 to 5, wherein the central station (10) is designed to control the switch state of the terminal elements (AG1, AG2) in the individual subscribers.
7. Alarm system according to any of claims 1 to 6, wherein the terminal element (R1, C) is positioned between the common connection point of the two line separators (LT1, LT2) and the other field bus wire.
8. Alarm system according to any of claims 1 to 6, wherein each of the subscribers has one terminal element (AG1) positioned upstream of the two line separators (LT1, LT2) and one terminal element (AG2) positioned downstream of the two line separators (LT1, LT2) between the wires of the field bus.
9. Alarm system according to any of claims 1 to 8, wherein the RC element (R1, C) comprises a parallel resistor (R2) for discharging the capacitor (C).
10. Method for operating an alarm system according to any of claims 1 to 9, involving a first data-transmission speed and a second, higher data-transmission speed for the communication between the central station (10) and the subscribers (1 to 8), wherein, in the event of a fault, the RC terminal elements (R1, C; AG1, AG2) of the final subscriber (4, 5) in each case on either side of the fault location are switched on only in the case of communication at the higher data-transmission speed.

Images