Abstract:
A building control or danger warning system includes a two-core circular bus for voltage supply and for communication with bus user circuits connected to the cores of the circular bus. The bus user circuits are looped-into the circular bus via FET (field effect transistor) polarity-reversal protection bridges, thereby simplifying connection of the bus user circuits to the circular bus. A bus user circuit is located between d.c. connection terminals and connected in parallel with two protection bridges. The bus user circuit measures the voltage conditions and polarity of the a.c. voltage input terminals of the bridges. According to the results of the measurement, the bus is relayed to the subsequent bus user circuit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of International Application No. PCT/EP2006/007181, filed on Jul. 20, 2006, entitled “Building Control or Danger Warning System,” which claims priority under 35 U.S.C. §119 to Application No. DE 102005037047.0 filed on Aug. 5, 2005, entitled “Building Control or Danger Warning System,” the entire contents of which are hereby incorporated by reference. 
   FIELD OF THE INVENTION 
   The device described herein relates to building control or danger warning system (i.e., an electronic alert system) with a two-core circular bus for voltage supply and for communication with bus users. 
   BACKGROUND 
   Known building control or danger warning systems include a two-core circular bus to which bus users (e.g., alarm systems) are connected in parallel. In case of an interruption of the circular bus, two stub lines that may be operated independently from each other remain. In case of a short-circuit, the segment concerned may be disconnected by separate circuit breakers that are controlled by a central control station of the building control or danger warning system, so that, for example, shortened but operational stub lines still remain available. 
   In the following, the term “signal system” is used to include building control or danger warning systems. 
   In the course of assembly of signal systems of this kind, the bus users connected to the circular bus, and the circuit breakers, must be looped-into the circular bus. Bus users that are provided with polarity reversal protection and can be connected rapidly are known. However, the circuit breakers must be connected with correct polarities. 
   Color-coded conductors simplify the assembly of the circuit breakers only to a limited extent, because there is no world-wide uniform standard for color coding. Therefore time-consuming determination measurements on individual cores cannot be avoided, in particular when existing plants are being extended. 
   Furthermore, signal systems are known in which circuit breakers, usually in the form of relays or FETs (i.e., field effect transistors), are incorporated in the bus users. Bus users of this kind are connected in series into the circular bus, with care being taken to ensure correctness of polarity. Although the incorporation reduces the outlay of assembly work, it is still necessary to perform time-consuming determination measurements on the individual cores. Signal systems of this kind are known from DE 36 14 692 A1, DE 43 22 841 A1, CH 651 688 A5, and EP 468 097 A2. 
   A bus user circuit that is usable for a signal system of the generic kind as previously mentioned is known from DE 198 50 869 A1. This bus user circuit has two circuit breakers, each of which connects two cores of the circular bus. Therefore a bus user fed from both sides must be connected to the bus with the same designated polarity despite the polarity-reversal protection bridge, so that in this case too, determination measurements must be performed on the individual cores. 
   SUMMARY 
   The device described herein relates to a building control or danger warning system (i.e., an electronic alert system) with a two-core circular bus for voltage supply and for communication with bus users, each bus user comprising a bus user circuit connected to each of the cores of the circular bus via a polarity-reversal protection bridge. The bus user circuits are looped-into the circular bus via FET (field effect transistor) polarity-reversal protection bridges, thereby simplifying connection of the bus user circuits to the circular bus. A bus user circuit is located between d.c. connection terminals and connected in parallel with two protection bridges. The bus user circuit measures the voltage conditions and polarity of the a.c. voltage input terminals of the bridges. According to the results of the measurement, the bus is relayed to the subsequent bus user circuit. 
   The described electronic warning system simplifies the assembly of building control and danger warning systems. In accordance with an exemplary embodiment of the electronic warning system, each bus user comprises two polarity-reversal protection bridges via which it is looped-into the circular bus. The polarity-reversal protection bridges consist of FETs that are, at first, in a non-conducting state. The d.c. voltage terminals of the two bridges are connected in parallel, and a bus user circuit is located between the d.c. voltage terminals. The bus user circuit measures the voltage conditions and their polarities at the a.c. voltage inputs of the bridges, and ensures the operation of the bus user and the circular bus by driving the FETs. Owing to their symmetrical construction, the bus users can be installed very rapidly. Input and output terminals are first determined during operation, and it is therefore immaterial which conductor is connected to which pair of terminals. Furthermore, no additional components are necessary for effecting a circuit-breaking operation, because via a switching of the FETs of the output side bridge into a non-conducting state, the bus segment located behind this can be disconnected. Another advantage is that during operation the feeding of the bus user can be effected via its previous output terminal. This may be necessary, for example, when the circular bus is separated into two stub lines. 
   According to an exemplary embodiment of the electronic warning system, the bus user circuit receives its supply voltage at first via parasitic diodes of two FETs that are located to be diagonally opposite to each other in a bridge. Subsequently, the bus user circuit measures the voltage conditions at the a.c. voltage input terminals of the bridges. When a voltage is applied at exactly one bridge, the FETs with current flowing through their parasitic diodes, and two FETs that are located to be diagonally opposite to each other in the other bridge, are switched to be conducting. Thereby the supply voltage is switched to the next bus user, or the circular bus is closed when the output of the bus user is connected to the central control station of the signal system. 
   According to a further embodiment, the bus user circuit holds all FETs in the non-conducting state when it detects a supply voltage at the a.c. voltage input terminals of both bridges. An equalization of the potential between the two feed voltages is thereby prevented. 
   In Germany, there is a regulation that a circular bus of a building control or danger warning system be fed only from one side during normal operation. In other countries (e.g., Great Britain) the feeding of a circular bus (e.g., a fire alarm system bus) is effected basically from both sides in order to keep voltage losses as low as possible. This case is reflected in another embodiment of the electronic warning system. Here a feeding from both sides is detected as being “correct”, and the corresponding FETs are rendered non-conducting. 
   In another advantageous embodiment, the bus user has available a self-sufficient current supply or a component for storing energy (i.e., a capacitor or battery), e.g., in the form of a gold cap condenser. This makes possible a rapid restoration of the circular bus following a short circuit. 
   In a further embodiment, the bus user circuit comprises a memory. The bus user circuit can store data in the memory, the data relating to, for example, operating conditions, faults in the bus, or instructions from the central control station. 
   In yet another embodiment of the electronic warning system, some of the bus users are signaling units. This makes it possible to monitor environmental and operational conditions and to report these conditions to a control station. Signaling units of this kind may be, for example, danger alarms (e.g., fire alarms). The operational conditions to be monitored may be, for example, conditions of doors, locks, windows, or smoke outlets. 
   The above and still further features and advantages of the present invention will become apparent upon consideration of the following definitions, descriptions and descriptive figures of specific embodiments thereof, wherein like reference numerals in the various figures are utilized to designate like components. While these descriptions go into specific details of the invention, it should be understood that variations may and do exist and would be apparent to those skilled in the art based on the descriptions herein. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS  
     In the following, the system will be farther illustrated with the aid of schematic drawings and flow charts, where: 
       FIG. 1  is a schematic drawing of a first exemplary embodiment; 
       FIG. 2  is a schematic drawing of a second exemplary embodiment; and 
       FIGS. 3   a  and  3   b  are flow charts. 
   

   DETAILED DESCRIPTION  
     FIG. 1  shows a bus user circuit for communication with a control station that is connected into a signal system via a two-core bus to a d.c. voltage supply. The bus user circuit comprises two pairs of terminals A 1 , A 2  and B 1 , B 2  via which the bus user circuit is connected in series into the bus system. Each of the pairs of terminals (connections) A and B is connected to a.c. voltage input terminals of a bridge rectifier BR 1  and BR 2 , respectively. The d.c. voltage output terminals of the two bridge rectifiers BR 1  and BR 2  are connected in parallel. The bus user circuit also is connected in parallel with these output terminals of the two bridge rectifiers BR 1  and BR 2 . The bridge rectifiers each consist of four FETs (BR 1  of T 1 , T 2 , T 3  and T 4 ; and BR 2  of T 5 , T 6 , T 7  and T 8 ). In order to make clear the manner of operation, the parasitic diode paths of the FETs (T 1  to T 8 ) have been additionally drawn as diodes D 1  to D 8 . The terminals A 1 , A 2 , B 1  and B 2  are each connected to ground via diodes D 9 , D 10 , D 11  and D 12  and resistors R 1 , R 2 , R 3  and R 4 . The bus user circuit determines via each of the terminals M_A 1 , M_A 2 , M_B 1  and M_B 2  the voltage drop at the resistors M_A 1 , M_A 2 , M_B 1  and M_B 2 , respectively. The FETs (T 1  to T 8 ) are driven according to the measurement results. If, for example, feeding is effected only via the pair of terminals A 1 , A 2 , then specifically the FETs having current-carrying parasitic diode paths, i.e., either T 1  and T 3 , or T 2  and T 4 , are first switched to be conductive. Subsequently, the bus is passed on to the connection B by suitable driving (see  FIG. 3 ) of the FETs T 5  to T 8 . 
     FIG. 2  schematically shows an embodiment in which the voltage conditions and the signs at the pairs of terminals A 1 , A 2  and B 1 , B 2  are determined via four optoelectronic couplers O 1 , O 2 , O 3 , O 4  instead of via the resistors R 1  to R 4  as in  FIG. 1 . Each of the terminals A, B is connected to two LEDs disposed antiparallel (A with LED 1  and LED 2 ; and B with LED 3  and LED 4 ). Each of the LEDs (LED 1  to LED 4 ) is a component of an optoelectronic coupler O 1 , O 2 , O 3  and O 4 , respectively. One of the output terminals of each optoelectronic coupler O 1  to O 4  is connected to ground and the other to the positive d.c. output terminals of the bridge rectifiers BR 1  and BR 2  via a resistor (O 1  via R 5 , O 2  via R 6 , O 3  via R 7 , and O 4  via R 8 ). The bus user circuit measures the voltage drop at each of the resistors R 5 , R 6 , R 7  and R 8  via the terminals M_A 1 , M_A 2 , M_B 1  and M_B 2 , respectively. When a d.c. voltage is applied to a terminal (A or B), exactly one optoelectronic coupler supplies a signal “0”. The input (A or B) and its polarity are determined from the information as to which optoelectronic coupler supplies the signal. If the circular bus is being fed with d.c. from both sides, then exactly two optoelectronic couplers that are assigned to different terminals A, B supply a signal “0”. The bus user circuit evaluates the signals from the optoelectronic couplers, and then drives the FETs T 1  to T 8  according to the signals, analogous to the case of  FIG. 1 . 
   The driving of the FETs T 1  to T 8  in dependence upon the signals at the terminals M_A 1 , M_A 2 , M_B 1  and M_B 2  is illustrated as a flow chart in  FIG. 3 . The chart starts with the bus user receiving a voltage, and all FETs being in a non-conducting state. The voltage at the terminals A 1 , A 2 , B 1 , and B 2  is then measured. If the feeding of the bus user circuit is effected via exactly one pair of terminals, then the corresponding FETs become conductive by an application of a suitable gate voltage. Apart from this, the bus is further relayed by driving of the gate of two FETs of the bridge that is not connected to the pair of input terminals. If, for example, the feeding is effected via the terminals A 1  and A 2  with the voltage at A 1  being positive in comparison with that at A 2 , then a gate voltage is applied to the FETs T 1  and T 3  via S_T 1  and S_T 3  in order to reduce the voltage drop at the diode paths. After it has been ensured that no voltage is being applied to the pairs of terminals B 1  and B 2 , the FETs T 8  and T 6  are driven via S_T 8  and S_T 6  in order to switch the bus onto the pair of terminals B 1  and B 2  that is now the pair of output terminals. 
   If the feeding is effected from both sides, i.e., a voltage is being applied also to the pair of terminals B 1 , B 2 , then this is ascertained and memorized (i.e., stored in memory), and can be reported to the central control station. 
   In another programming of the bus user circuit, for example, for application in a system with obligatory feeding of the circular bus from both “ends” connected to the central control station, the bus user circuit switches through the corresponding FETs of both bridges BR 1  and BR 2 . 
   If the voltage supply collapses, and the bus user circuit comprises an energy store (i.e., a capacitor or battery), for example, in the form of a gold cap condenser, then the bus user circuit can detect the voltage supply collapse as being a fault, and can store and report the fault to the central control station following a restoration of the circular bus. Accordingly, a programmed reaction can occur at the central control station, for example, a malfunction report, possibly attended by actuation of a telephone-line selector, or an entry into an event memory. 
   While the invention has been described in detail with reference to specific embodiments thereof, it will be apparent to one of ordinary skill in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Accordingly, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.