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BK7500, BK7520 | SERCOS interface Bus Couplers

The Bus Couplers BK7500 and BK7520 connect the SERCOS bus system with the electronic terminal blocks, which can be extended in modular fashion. One unit consists of one Bus Coupler, any number from 1 to 64 terminals and one end terminal.

Compared with the Bus Coupler BK7500, the BK7520 allows, with the K-bus extension technology, the connection of up to 255 Bus Terminals to one Bus Coupler. The Bus Coupler recognises the connected terminals and automatically generates the affiliations of the inputs/outputs to the bytes of the process image.

SERCOS interface is a fibre optic bus that was developed for use in drive technology as a digital drive interface for drives. SERCOS is an open fieldbus system, which since 1995 has been subject to the international standard IEC 61491 for numerically controlled machines. It is widely used in the drive technology sector.

The bus consists of a master and of a number of slaves. In SERCOS, most of the slaves are drive amplifiers. The bus topology is a ring system, in which it is possible to operate up to 254 stations. The transmission speed is 2 and 4 Mbaud. The BK7520 supports additionally 8 and 16 Mbaud. There are basically three types of telegrams. The master SYNC telegram is received by all the slaves at the same time, and is used for synchronisation. The master data telegram is also received by all the slaves, and contains the cyclic data and the service data. The slaves send their data in what is known as a drive telegram.

Complex signal processing for analog I/Os, position measurement, …

The BK7500 and BK7520 Bus Couplers support the operation of all Bus Terminals and have been specified in accordance with SERCOS I/O and SERCOS interface.

The analog and multi-functional Bus Terminals can be adapted to each specific application using the KS2000 configuration set. Depending on the type, the analog Bus Terminals' registers contain temperature ranges, gain values and linearisation characteristics. With the KS2000, the required parameters can be set on a PC. The Bus Terminals store settings permanently and in a fail-safe manner.

Optionally, the Bus Terminals can also be controlled by the control system. Via function blocks (FBs), the programmable logic controller (PLC) or the Industrial PC (IPC) handles configuration of the complete periphery during the start-up phase. If required, the controller can upload the decentrally created configuration data in order to centrally manage and store this data. Therefore, new adjustments are not necessary in the event of replacement of a Bus Terminal.

Parameterisation can also be carried out via the SERCOS interface.


Technical data BK7500 BK7520
Number of I/O stations 254
Number of I/O points depending on controller
Data transfer medium 1,000 µm plastic fibre optic
Distance between stations 40 m plastic fibre optic
Data transfer rates 2/4 Mbaud 2/4/8/16 Mbaud



Technical data BK7500 BK7520
Number of Bus Terminals 64 64 (255 with K-bus extension)
Max. number of bytes fieldbus 32 byte input/32 byte output for the cyclic interface (depending on the master) 254 word I/O for the cyclic interface (depending on the master)
Digital peripheral signals 256 inputs/outputs 1,020 inputs/outputs
Analog peripheral signals 128 inputs/outputs 254 inputs/outputs
Configuration possibility via KS2000
Data transfer rates 2/4 Mbaud, adjustable by means of configuration switch 2/4/8/16 Mbaud, adjustable by means of configuration switch
Bus interface F-SMA standard, IEC 872-2
Power supply 24 V DC (-15 %/+20 %)
Input current 70 mA + (total K-bus current)/4, 500 mA max.
Starting current 2.5 x continuous current
Recommended fuse ≤ 10 A
Current supply K-bus 1,750 mA
Power contacts 24 V DC max./10 A max.
Electrical isolation 500 V (power contact/supply voltage/fieldbus)
Weight approx. 170 g
Operating/storage temperature 0…+55 °C/-25…+85 °C
Relative humidity 95 %, no condensation
Vibration/shock resistance conforms to EN 60068-2-6/EN 60068-2-27
EMC immunity/emission conforms to EN 61000-6-2/EN 61000-6-4
Protect. class/installation pos. IP 20/variable
Approvals CE, UL, Ex



KS2000 configuration software for extended parameterisation
Cordsets cordsets and connectors
FC750x-0000 PC Fieldbus Cards with PCI interface



Ordering information  
BK7500 SERCOS interface Bus Coupler for up to 64 Bus Terminals
BK7520 SERCOS interface “Economy plus” Bus Coupler for up to 64 Bus Terminals (255 with K-bus extension)