Terminating resistors (internal and external BMS bus) Technical aspects affecting the use of BENDER communication solutions The BMS bus must be terminated at both ends with terminating resistors of 120 Ω (0.25 W). The resistances are to be connected in parallel to the terminals A and B. A BMS bus not being terminated may become unstable and may cause malfunctions. Basic rules for the design of a BMS bus 1. Every BMS bus must be controlled by a master.2. Only one master may exist in each BMS bus system. 3. Every device on the BMS bus must be assigned its own unique address.4. Never assign one address twice.5. The BMS bus must be terminated at both ends withterminating resistors of 120 Ω.6. The cable length must not exceed 1200 m, but can beextended by a DI-1 repeater.7. The number of devices on a BMS bus must not exceed 32, but the bus reach can be extended by DI-1 repeaters (DI-2 or DI-3).8. The BMS bus must provide a favourable topology(without branch circuits).9. The bus cable (J-Y(ST)Y 2 x 0.6) must be shielded and earthed at one side.10. Take care not to mix up bus terminal A and B. 1. BMS bus The BMS bus (BENDER Measuring Device Interface) is BENDER's own development and enables optimum data exchange between all communication-capable BENDER products. The BMS bus is an RS-485 interface utilizing a protocol especially developed for BENDER devices. The BMS bus transmits alarm and status messages on a cyclic basis. In addition, the protocol includes commands for requests and for device parameter changing and various control commands. Cables and cable lengths (internal and external BMS bus) The specification of the RS-485 interface limits the maximum length of the interface to 1200 m. With longer cables, additional measures are necessary (installation of a DI-1 repeater). The inter-face cable should be a shielded cable. A suitable cable type is, for example, J-Y(ST)Y 2 x 0.6. If interface cables are implemented as spur cables, the maximum length is limited to 1 m. If longer spur cables are used, safe communication cannot be guaranteed. The number of devices on a bus must not exceed 32. By using repea-ters (e.g. BENDER DI-1) another 32 devices can be connected or the cable length can be extended by another 1200 m. Function – Master-Slave principle The BMS bus works according to the Master-Slave principle. That means, one device is the master whereas all other devices areslaves. Hence, only one master may exist on each BMS bus. The master requests all devices on the bus on a cyclic basis, listens to their signals and carries out the respective commands. During operation the master function can temporarily be taken over bya slave. Every device on the BMS bus must be assigned its own unique address. Address 1 is assigned to the master. Internal and external bus Several BMS bus systems can be interconnected to one common system. For this purpose, one MK800 control and indication panel or one TM operator panel is required for each of the systems. Several MK800 or TM operator panels communicate with each other via the external bus. A consecutive address must be as signed to each device. The master function is passed sequentially according to the passing-token principle. That means, the master function is passed sequentially to each MK800 or TM operator panel so that only one station may talk at a time. On the internal bus each TM operator panel communicates with devices of the associated BMS system. The respective device is the master with address 1 assigned to it. Addresses and address ranges Every device on the BMS bus must be assigned its own unique address. Address 1 is assigned to the master. Address 000 is the "broadcast address” which addresses all other nodes and may therefore not be assigned to any other device. 150 of 255 ad-dresses theoretically available (1 byte address, also 28 = 256) arecurrently used. This is due to address ranges defined for special device families. Master redundancy Some BMS devices such as FTC470XDP, FTC470XMB, FTC470XET and MK2430 are capable of acting as redundant Master. In the event of failure of the regular master (bus address 1) after approx-imately 60 seconds such a device takes over the Master function in order to control the BMS bus. If the regular master becomes active again, the FTC470XET returns the master function. These devices automatically take over the redundant master function. Interrogation of all connected devices (internal BMS bus) During normal operation, the master transmits a request to every device within the address range for the number of alarm mess- ages. If alarm messages are present, all channels of the respective device are requested. Then the address ranges are requested for the number of operating messages and if messages exist, the channels of the respective devices are requested too. In addition, every other second all slaves are requested for possible inter- ruptions via the broadcast address 0. That ensures that new alarm messages are available on the bus within two seconds at thelatest.
Annex 1.9.3 190 Main catalogue part 1 – 08.2007/Insulation monitoring