Abstract:
The invention relates to a method for commissioning a bus system and to a corresponding bus system. A test is carried out preferably after installation of the bus system and before it is actually put into operation to check whether the system is functioning properly. The test can comprise several stages which each test different functional aspects of the bus system. The bus system test can be carried out especially from a distributor or gateway ( 1 ) which couples several voltage supply lines ( 2-4 ), designed to carry information in addition to a supply voltage, with a central voltage supply line (L, N).

Description:
IDENTIFICATION OF RELATED APPLICATIONS 
     This is a Continuation of International Application PCT/EP99/01598, filed Mar. 11, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for commissioning a bus system which comprises at least one voltage supply line by way of which, on the one hand, a supply voltage is applied to loads that can be connected thereto and, on the other hand, information is transmitted, and also to a corresponding bus system, in which by way of at least one voltage supply line, on the one hand, a supply voltage is applied to loads that can be connected thereto and, on the other hand, information, for example control information, is transmitted. 
     2. Description of the Related Art 
     Bus systems, in which the main power lines leading to the individual components and loads are used as the bus line, have been known for a comparatively long period of time. 
     A corresponding bus system for use for building services management system installations is known, for example, from PCT/EP 97/06577, in which various loads (actuators), such as, for example, lights, blinds, air-conditioning installations or the like, are connected to the bus system. Moreover, information in order to be able to activate the individual loads with the aid of this information or to be able to transmit corresponding check-back signal information is transmitted by way of the main power lines provided for these loads. The information that is transmitted in this way by way of the main power lines is as a rule transmitted at a frequency that is higher by orders of magnitude than the actual main frequency of the bus system, with in particular the useful band, which is used for the transmission of information, lying above 100 kHz. The loads can decouple the individual information signals from the low-frequency supply voltage signal by way of appropriately configured filter circuits. 
     As a rule, the information is transmitted by way of the main power lines merely within one subnetwork which is connected to the central supply voltage line by way of a band-stop filter arrangement and also a distributor device (gateway). By using band-stop filters it is possible to isolate the individual subnetworks from the rest of the network. In this connection, an improved measure has been proposed in PCT/EP97/06577, namely that for each branch line corresponding to a subnetwork a separate band-stop filter be provided, connected between the distributor device (gateway) and the corresponding branch line. The advantage of this arrangement, in comparison with an arrangement in which a central band-stop filter is connected between the central supply voltage line and the distributor device, is that the individual band-stop filters can be set up in a less complex manner than a single central band-stop filter and, moreover, the information signals cannot reach the central main-voltage busbar of the distributor, something which could otherwise result in great attenuation of the information signals. Moreover, disturbances within a branch line are not transmitted directly to the other branch lines or subnetworks. 
     In addition to different loads it is also possible to connect any sensors, interfaces or control units to the individual branch lines or supply voltage lines respectively so that communication between the individual components of the bus system is possible with the aid of the previously mentioned transmission of information by way of the corresponding supply voltage line. 
     Furthermore, a control system is known from PCT/EP90/01133 for a plurality of loads that are arranged in a distributed manner and which can be activated by a central control station or control unit so that in this way it is possible to set different load types in a decentralized manner. Each load stores a source address which is transmitted to the control station by the respective load before the control system is actually commissioned. Subsequently, the control station scans the corresponding loads by addressing the individual source addresses in order in this way to obtain information on the spatial arrangement and type of the respective load. Furthermore, the individual loads are associated with specific groups or arrangements of loads, with the control station subsequently storing an operating address in the individual loads that corresponds to the respective group association. In this way, loads that are linked together centrally in groups or loads of a specific load type can be set by the control station, with, moreover, the greatest possible flexibility of the control system being guaranteed by the address administration. The control system described in PCT/EP90/01133 does not, however, relate explicitly to the bus systems described by way of introduction and in which, together with the supply voltage signal of low frequency, information signals of higher frequency are simultaneously transmitted by way of mains power lines. 
     The reliability of transmission, that is, the guarantee of sufficient quality of the transmission of information signals, constitutes one particular problem of the bus systems previously described. In this connection, it is possible that disturbances can occur not only on the forward channel, that is, from the gateway or distributor to the individual loads, but also on the backward channel, that is, from the individual loads to the distributor, as a result of which disturbances the information signals, such as, for example, control signals or check-back signals can not be transmitted with sufficient quality or even can no longer be received so that, in that case, it is not possible for the bus system to operate properly. 
     Proper operation is essential, for example, in the case of bus systems which are used in airplanes. For this reason, for example, the ARINC 629 bus used in airplanes of the Boeing 777 type contains a plurality of safety systems by means of which the failure of a system element is automatically identified and offset by the use of an identical replacement element. However, when viewed from the outside it is not readily apparent whether a bus user or the branch cable used to connect the bus users to the bus lines is defective in part. In the article “Testing the Subscriber Interface to the ARINC 629 Current Mode Bus” in the journal “Proceedings of the Systems Readiness Technology Conference (AUTOTESTCON)”, Anaheim, September 1994, pages 653-661, a test system is therefore put forward, by means of which system it is possible to examine the branch cable in a controlled manner to check whether it is functioning fully in a proper manner. To this end, a test module has been developed that is connected to the branch cable and the bus user connected thereto and which, by transmission and simulation of bus signals and also by evaluation of the signals which occur in the branch cable, carries out a full function test that includes monitoring whether the replacement elements are functioning properly. 
     Whilst the test system described in this article does investigate the individual branch cables in an extremely precise manner, it is not able to examine the bus system as a whole to check whether it is functioning properly. For example, it is not possible to identify whether the bus lines are functioning properly and the users are correctly connected to the bus, since the units which are to be tested are directly connected to the test module. 
     The underlying object of the present invention is therefore to facilitate the commissioning of the bus system outlined by way of introduction and also to guarantee at the same time sufficient security against loss of quality or against disturbances by examining the ability of the bus system as a whole to function properly by means of a test which can be carried out in a simple manner. 
     SUMMARY OF THE INVENTION 
     The object is achieved in accordance with the present invention by means of a commissioning method which comprises the steps of 
     a) installing the bus system; 
     b) testing whether the bus system is functioning properly; and 
     c) operating the bus system, 
     wherein step b) comprises the step of carrying out a plurality of test phases in succession, wherein different aspects of the bus system&#39;s ability to function properly are tested, and 
     including during a first test phase the step of testing the correct connection of loads, sensors and/or control devices to respective voltage supply lines. 
     According to the present invention for commissioning purposes a function test is carried out after the bus system has been installed and before it is actually put into operation, with this test including a plurality of test phases which are carried out in succession and which test different aspects of the bus system&#39;s ability to function properly. In particular, in this connection during a first test phase the connection of loads, sensors and/or control devices to the correct respective voltage supply is tested. For the case where a plurality of subnetworks or branch lines, by way of which information signals are to be transmitted together with the supply voltage signal of low frequency, are connected to the central voltage supply line by way of the distributor or gateway that has previously been described, it is advantageously provided that the individual subnetworks to be tested separately or individually so that whilst one branch line is being tested, the other branch lines are without current. 
     According to a preferred exemplary embodiment, the test comprises three test phases. Thus, the first test phase, in addition to examining whether the loads, sensors or control units are correctly connected, can also examine whether the safety functions of the loads, implemented as standard if applicable, are reacting correctly. With the aid of a second test phase it is possible to test the sending capacity of the gateway or distributor and also the receiving capacity of the individual loads, sensors or control units. After the run-through of this second test phase, it is thus established whether all the loads can correctly understand the messages that are sent by the gateway. Finally, with the third test phase it is possible to test the transmission of information by way of the backward channel of the bus system, that is, from the loads or actuators to the gateway, by evaluating the quality of the check-back signals or status information transmitted by the loads. 
     The gateway used in the case of the bus system in accordance with the present invention is used in the first place as an interface between a central supply voltage and the individual subnetworks or branch lines by way of which transmission of information is to take place together with the supply of voltage. The distributor, however, can also have a functionality that is peculiar to it, such as, for example, the commissioning function. Likewise, however, it is also possible for the commissioning or test function to be carried out by a control device which is connected to one of the bus lines and which by way of the distributor communicates with the individual subnetworks which are provided for the purpose of transmitting information. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described in greater detail in the following with reference to a preferred exemplary embodiment. 
     FIG. 1, by way of example, shows the structure of a preferred exemplary embodiment of a bus system in accordance with the present invention; 
     FIG. 2 shows a representation for the purpose of explaining the basic sequence of a preferred method in accordance with the present invention for commissioning the system shown in FIG. 1; and 
     FIGS. 3 a  and  3   b  show representations in the form of a flow chart for the purpose of explaining the method of the present invention shown in FIG. 2 in a more detailed manner. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a central voltage supply line or main power line having a current-carrying conductor L and a neutral conductor N. Connected to this central mains power line there is a distributor or gateway  1  by means of which there branch off from the central mains power line a plurality of further voltage supply lines  2 - 4  which form subnetworks or electric circuits for the bus system and are used for supplying voltage to loads  10 ,  20  and  30 , connected to these voltage supply lines  2 - 4 , and also for transmitting information. 
     The transmission of information by way of the individual voltage supply lines  2 - 4  is effected in a frequency band that is higher by a plurality of orders of magnitude than the low alternating voltage frequency of the mains voltage that is applied to the central mains voltage line L, N. The subnetworks, which are used for the transmission of information and are formed in particular by the voltage supply lines  2 - 4  that are branched off, are separated from the central mains power line L, N by band-stop filters  100 ,  110  and  120 . According to the configuration shown in FIG. 1, the band-stop filters  100 ,  110  and  120  are arranged between the voltage-supply lines  2 - 4  used for the transmission of information and the distributor  1  and represent stop filters for the frequency ranges used for the transmission of information. However, in order to enable there to be transmission of information between the individual voltage supply lines  2 - 4  as well, according to FIG. 1 the individual band-stop filters  100 ,  110  and  120  are connected by way of a two-phase bus line  5  and each have a coding and decoding unit  101 ,  111  and  121  respectively for coding and decoding the information that is to be transmitted and also a sending and receiving unit  102 ,  112  and  122  respectively for sending and receiving the information that is transmitted. Consequently, it is not only possible to transmit information on the individual voltage supply lines  2 ,  3  and  4 , but it is also possible to transmit information between the individual voltage supply lines  2 ,  3  and  4 . 
     The bus or building services management system shown in FIG. 1 includes a plurality of different loads which can be arranged, for example, in different rooms of a building and can be connected to the individual voltage supply lines  2 - 4 . In particular, a lighting device  10 , an air-conditioning installation  20 , which is used to regulate the temperature of and ventilate a room, and also a blacking-out device  30 , for example a blind with a corresponding driving motor, are shown in FIG.  1 . These loads are supplied with the mains voltage by way of the voltage supply lines which are connected to the loads in a corresponding manner. Moreover, the voltage supply lines, which are connected to the loads, are used for the transmission of information between the distributor  1  and the loads or between the distributor  1 , the loads and, moreover, sensors  70 ,  80  and control units  40 ,  50  and  60  connected to the voltage supply lines  2 - 4 . Since each load  10 ,  20  and  30  is to be able not only to send, but also receive information, each load advantageously has a coding and decoding unit  11 ,  21  and  31  for coding and decoding the information that is to be transmitted and also a sending and receiving unit  12 ,  22  and  32  for sending and receiving the information that is to be transmitted. 
     Each control unit  40 ,  50  and  60  that is connected is generally used to control the transmission of information by way of the bus system and therefore also has a coding and decoding unit  41 ,  51  and  61  for coding and decoding the information that is to be transmitted and also a sending and receiving unit  42 ,  52  and  62  for sending and receiving the information that is to be transmitted. An operator can intervene manually in the transmission of information by way of the control units  40 ,  50  and  60  by selecting, by way of specific selection keys  45 ,  55  and  65  respectively of the control units, a specific load or a specific load type and by changing, by way of setting keys  44 ,  54  and  64  respectively, a specific operating parameter of the load type selected or the load selected, such as, for example, the brightness of the room or the temperature of the room. The individual loads are thereby addressed with the aid of addresses, with an individual address being associated with each load. The information that is transmitted from the corresponding control unit by way of the subnetwork used for the transmission of information is received by the load that is addressed or by all the loads that are addressed, decoded and converted into corresponding control signals so that the brightness of the lighting device  10 , for example, is automatically regulated. Vice versa the operating state or the operating parameters of the individual loads is or are transmitted by the sending units  12 ,  22  and  32  of the loads by way of the building services management system so that each control unit  40 ,  50  and  60  can indicate the instantaneous state in displays  43 ,  53  and  63  respectively. It is also possible for scenarios predetermined by way of the selection keys  45 ,  55  and  65  of the control units  40 ,  50  and  60  respectively to be called up and for the individual loads or load types to be activated and set in accordance with a selected scenario. Thus, for example, a selection key can be assigned in such a way that after it has been actuated the lighting device  10  is dimmed to the value “semi-dark” and the room temperature is set to 20° C. by way of the air-conditioning installation  20  and also in a further room the blind  30  can be moved into the “semi-closed” position. A possible embodiment of the control units  40 ,  50  and  60  is described, for example, in DE-OS 94 12 900. 
     The sensors  70  and  80 , which are also connected to the subnetwork that is used for the transmission of information enable the individual loads to be regulated automatically, since these sensors  70  and  80  also have a coding and decoding unit  71  and  81  respectively for coding and decoding the information that is to be transmitted as well as a sending and receiving unit  72  and  82  respectively for sending and receiving the information that is to be transmitted. FIG. 1, for example, shows a light sensor  70  for monitoring the brightness of the room and also a temperature sensor  80  for monitoring the internal or external temperature. 
     The actual values delivered by the sensors  70  and  80  are likewise transmitted by way of the voltage supply lines  2 - 4  to the control units  40 ,  50  and  60  so that these can automatically generate and transmit corresponding control signals for the individual loads. 
     Moreover, as shown in FIG. 1, it is also possible to connect to the building services management system an interface  90  to which, for example, further building services management systems can be connected or which can be provided to receive external control signals, for example from a computer or a remote control. Since the interface  90  also has to be able to transmit information data, the interface  90  likewise has a coding and decoding unit  91  and also a sending and receiving unit  92 . 
     In general, the bus or building services management system shown in FIG. 1 enables information to be transmitted between the distributor  1  and the individual loads  10 ,  20  and  30 , sensors  70  and  80 , the interface  90  and also the control units  40 ,  50  and  60  irrespective of the arrangement in the individual rooms of the building services management system, with it being possible to use any known coding method, in particular PCM coding, to code the information that is to be transmitted, and also any known transmission method, in particular the so-called spread technique (SSMA, Spread Spectrum Multiple Access), to transmit the information. 
     The transmission system shown in FIG. 1 is influenced very greatly by the line conditions so in accordance with the present invention a test mode is integrated in the bus system shown in FIG.  1 . In the exemplary embodiment shown in FIG. 1 in particular the control unit  50  connected to the distributor or gateway  1  is responsible for carrying out this test mode. Instead of this, however, it is also possible for the test function to be additionally performed by one of the control units  40 ,  60  connected to the branch lines  3  or  4 . It would also be possible for the distributor  1 , for its part, to form an independent control unit which can carry out all the control and test functions. The test function integrated in the bus system shown in FIG. 1 enables the communication functions of the individual subnetworks of the bus system to be controlled in a simple manner. The general function of this test mode shall be explained in greater detail in the following with reference to FIG.  2 . 
     In general, FIG. 2 shows the sequence of the method for commissioning the bus system shown in FIG.  1 . Basically installation of the bus system is to be carried out in the first instance (Step S 100 ). In general, the assembly and connection of all the components of the bus system, that is, of all the control units, loads and lines and so on, are understood by the term installation. By means of the installation therefore in the first instance the wiring of the individual components of the bus system in terms of circuit engineering as shown in FIG. 1 is realized. The function test proposed in accordance with the invention (Step S 200 ) follows the installation of the bus system. The proper functioning of the individual components of the bus system and also the communication paths between the individual components can be examined with the aid of the function test. In particular, the test mode can comprise a plurality of test phases, in which in accordance with the preferred exemplary embodiment in total three test phases  1 - 3  are run through in succession (S 210 , S 220 , S 230 ), each of which tests different functional aspects of the bus system. With the aid of the first test phase it is possible to test whether all the loads or actuators of the bus system are being supplied by the correct subnetwork or the correct electric circuit and whether their safety functions are reacting and responding correctly. With the aid of the second test phase, for example, it is possible to test whether all the loads or actuators of the bus system can correctly understand the messages or control commands transmitted by a control unit so that, on the one hand, the sending function of the control unit and, on the other hand, the receiving function of the loads can be tested. Finally, with the aid of the third test phase it is possible to test the transmission in the direction from the load to the testing control unit  50  which, in accordance with FIG. 1, is coupled to the distributor or gateway  1 . If all the test phases have been run through in an error-free manner, the system enters a waiting state (S 240 ) which can only be left, for example, by switching on the main switch  6  of the bus system (power-on-reset) shown in FIG. 1 or by invoking the test function at the control unit  50  again. Advantageously, the individual test phases for each subnetwork or for each voltage control line  2 - 4  are carried cut individually in succession so that in accordance with the exemplary embodiment shown in FIG. 1 the test phases S 210 -S 230  have to be run through three times in total before going over to the actual operation (Step S 300 ). Configuration of the individual control units  40 ,  50  and  60 , that is, the programming of predetermined scenarios or day-light characteristics which can be stored under the individual selection keys  45 ,  55  or  65  of the control units  40 ,  50  and can be subsequently called up, also occurs at the same time as the actual commissioning (S 300 ). During the operation it is also possible for addresses to be associated with the individual loads in order to be able to address the individual loads roomwise or groupwise or else even individually. 
     The test method proposed in accordance with the present invention shall be explained in greater detail in the following with reference to the flow chart which is shown in FIGS. 3 a  and  3   b.    
     As has already been explained before, each circuit used for the transmission of information, that is, each of the voltage supply lines  2 - 4  of the bus system shown in FIG. 1, is tested individually so that during the test carried out on one of these subnetworks all the other subnetworks or circuits are switched so as to be without current. For this purpose, associated with each circuit there are switches or fuses  7 - 9  which can be opened and closed manually or else even automatically by the control or test unit  50 . As shown in FIG. 1, in the first instance merely the voltage supply line  2  is connected to the central voltage supply line L, N, since merely the switch  7  is closed, whilst the switches  8  and  9  are open so that the voltage supply lines  3  and  4  are isolated from the central voltage supply line L, N. Thus in the following it is assumed that in the first instance it is the voltage supply line  2  with its corresponding subnetwork that is being tested. 
     The test mode is started in that a voltage supply line that is to be tested, that is, in the present case the voltage supply line  2 , is supplied with current and at the same time a test key  56 , which is provided on the control unit  50  coupled to the distributor or gateway  1 , is held pressed down. Therefore in accordance with FIG. 3 a  in a first step in the first instance it is examined whether the main switch  6  of the bus system shown in FIG.  1  and also at least one of the switches  7 - 9  is switched on. If this is not the case, in the first instance the bus system remains in a waiting state. If, on the other hand, the main switch  6  is switched on, it is subsequently examined whether the test key  56  shown in FIG. 1 is also pressed down (Step  102 ). If this is not the case, this means that the test mode is not to be started so it is possible to proceed to the normal operating mode (S 300 ). 
     If, on the other hand, when switching on the power supply the test key  56  at the distributor  1  or at the control unit  50  coupled thereto is pressed down at the same time, the first test phase is started (S 210 ). In this first test phase merely the subnetwork that is to be tested or the voltage supply line  2  that is to be tested respectively is supplied with current without any information being transmitted by way of this voltage supply line  2  by the control unit  50  which is used as the test unit. As a rule, integrated in the individual loads or actuators there are safety functions which in the case of a break in communication or a failure of the central control unit (that is, if there is no transmission of information) leads to a specific action of the respective load so that, for example, if a break in communication occurs the lighting device  10  is switched to maximum brightness or the blind  30  is opened fully. In the first test phase the distributor  1  or the control unit  50  coupled thereto is inactive so that no information is transmitted by way of the forward channel and a break in communication or a central failure is simulated in respect of the loads of the circuit that is to be tested. Moreover, each of the sensors or interfaces  70 ,  80  and  90  connected to the bus system as well as each control unit  40 ,  50  and  60  and each switch or key, connected thereto if applicable, has a status light-emitting diode (status LED)  73 ,  83  and  93 , and  46 ,  57  and  66  respectively, which is switched so as to flash during this first test phase, in which case in particular the flashing pattern of the sensors that are to be tested is switched in line with the flashing pattern of the light-emitting diode  57  at the test or control unit  50 . During the first test phase this flashing pattern is comparatively rapid so the light-emitting diodes are, for example, each switched on or off at intervals of 0.5s. 
     Subsequently, in Step S 211  it is tested whether the loads which are connected to the supply voltage line that is to be tested have responded correctly to the simulated break in communication. As a rule, the safety functions integrated in the individual loads are such that in the case of a break in communication, that is, in the case where no information is being transmitted by way of the voltage supply lines, the outputs of the individual loads are set at 100% power output so that in particular, for example, the lighting device  10  in this case is switched to maximum brightness. In Step S 211  it is consequently examined whether the loads which are connected to the supply voltage line that is to be tested have attained a power output of 100% within a specific time span, in particular within 1s. Since in accordance with FIG. 1 in particular it is the supply voltage line  2  that is being tested, in Step S 211  it is therefore tested whether within  1 s the lighting device  10  has been switched to maximum brightness and the air-conditioning installation  20  has been switched to maximum power output. Moreover, in Step S 211  it can be examined whether the status LED&#39;s of the corresponding sensors, keys, control units and so on actually flash in line with the status LED  57 . If no error could be identified in Step S 211 , the first test phase is terminated. If, on the other hand, an error is identified in Step S 211 , attempts must be made to eliminate this error and the first test phase with Steps S 210  and S 211  is run through anew. 
     All in all therefore with the first test phase it is possible to verify whether all the loads or actuators of the bus system are being supplied by the correct subnetwork or the correct supply voltage line and whether the safety functions of the individual loads are reacting correctly. 
     By pressing down the test key  56  on the control or test unit  50  of the distributor  1  again, it is possible to start the second test phase (Step S 212 ). 
     In the second test phase (Step S 220 ), all the loads connected to the supply voltage line to be tested are set jointly to a specific power-output value, for example to 10% power output, by the control or test unit  50  with the aid of corresponding control information or a corresponding broadcast message. During the second test phase, the loads are not therefore addressed individually, but activated together by means of a common control command. Furthermore, the status LED&#39;s of the corresponding sensors, keys or control units are again switched so as to flash in line with the flashing pattern of the status LED  57  of the test or control unit  50 , in which case in the second test phase the flashing pattern is slower than in the first test phase so that the light-emitting diodes are, for example, in each case switched on or off for periods of 1s. 
     In Step S 221 , it is subsequently examined whether the loads connected to the voltage supply line to be tested have actually been set to the desired power-output value. It is also possible to examine whether the status LED&#39;s of the corresponding sensors, control units or keys have actually been switched so as to flash. In the present case, in particular in Step S 221 , it is examined whether the lighting device  10  connected to the voltage supply line  2  has been dimmed to a brightness value corresponding to a power output of 10% and the air-conditioning installation  20  has been set to a temperature output of 10%. It is also examined whether the status LED  73  provided on the light sensor  70  is flashing in line with the flashing pattern of the status LED  57  of the control unit  50 . If no error is identified during step S 221 , the second test phase is terminated. If, on the other hand, an error did occur during the second test phase, after elimination of the error the second test phase can be recommenced from the start. 
     After the second test phase has been run through successfully, it is thus established whether all the loads of the supply voltage line that is to be tested can correctly understand the information or messages sent by the control unit  50  so that with the aid of the second test phase it is possible to test whether the individual users of the bus system can receive information, transmitted by way of the forward channel of the bus system, with a certain degree of quality. All in all therefore during the second test phase, on the one hand, the sending function of the control unit  50  or the distributor  1  respectively is tested and, on the other hand, the receiving function of the individual users is tested. 
     In a supplementary manner, during the second test phase it can be provided that the control unit  50  or the distributor  1 , moreover, search for loads that are connected to the respective voltage supply line that is to be tested. 
     By means of further actuation of the test key  56  provided on the control unit  50  it is possible to proceed to the third test phase (Step S 222 ). 
     During this third test phase the control or test unit  50  or the distributor  1  searches for loads that are connected to the voltage supply line that is to be tested or the subnetwork that is to be tested and requires the loads that are connected to transmit the addresses, which are allocated to them, by way of the bus system so that these addresses can be stored by the control unit  50  or the distributor  1 . Subsequently, the control unit  50  is able to address and set the individual loads individually in succession by sending a corresponding control command. In particular it can be provided that after the load addresses have been scanned, the individual loads can be run individually in succession, by being addressed in a corresponding manner, from 10% power output to 0% power output so that subsequently the user, who is putting the system into operation, can see from the changes in state of the individual loads whether the communication by way of the bus system is functioning in both directions, that is, both by way of the forward channel and by way of the backward channel. During the third test phase, moreover, the status LED&#39;s at the respective sensors, control units and keys are permanently switched on or off analogously to the status LED  57  of the control unit  50  in order to signal the third test phase. 
     During the third test phase (Step S 230 ) the loads of the voltage supply line to be tested can also be adjusted by keys or control units connected, if applicable, to the respective voltage supply line. 
     During a Step S 231  it is subsequently examined whether the check-back signals, sent in consequence of an adjustment or addressing of the loads of the voltage supply line to be tested, could be received with sufficient quality by the distributor  1  or the control unit  50  coupled thereto. A display means, which indicates whether the signal quality of all the check-back signals/messages of the individual loads suffices or not, can optionally be provided on the control unit  50 . In particular, the display  53  that is already provided on the control unit can come into consideration for this purpose. 
     If, however, in Step S 231  it has been identified that not all the check-back signals could be received correctly, after the fault has been eliminated the third test phase is to be run through anew. 
     In general therefore the transmission of check-back signals from the loads to the distributor  1  and also the receiving capacity of the distributor  1  or the control unit  50  respectively is tested with the aid of the third test phase. 
     If no error has been identified in the third phase either, the status LED  57  on the control unit  50  is finally permanently switched off, thereby signalling the end of the test mode. The bus system, however, is not yet ready for normal operation, but first enters a waiting state S 240  in which the bus system or the distributor  1  remains for so long until the test key  56  on the control unit  50  is actuated anew or a power-on-reset-command, that is, renewed actuation of the main switch  6  of the bus system, has been identified. The waiting state (S 240 ) shown in FIG. 3 b  is thus equivalent to an examination in accordance with steps S 101  and S 102  (cf. FIG. 3 a ). When the current is switched on again without pressing down the test key  56  on the control unit  50 , the bus system or the distributor  1  goes over into the normal operating mode (S 300 ). 
     In the flow chart shown in FIGS. 3 a  and  3   b  it is assumed that when an error occurs merely the corresponding test phase has to be repeated. Instead of this, however, it is also possible that, when an error occurs and is identified, the whole test, starting with the first test phase, is repeated.