Fieldbus Comparison

Fieldbus Packages

 

General Information about Fieldbus Systems

 

A serial bus system designed for industrial real-time data communication is called fieldbus. It provides communication between a bus master and remote slave stations, or distributed actors/sensors in order to read and write process data. Sensor/actor fieldbus systems are designed for low latency and low transmission volumes.  Their packet sizes are in general in the range of up to 200-300 bytes.  The transmission speed can be chosen in a wide range from e.g. 12Mbit/s down to 1200bit/s. The useable segment length depends on the transmission speed, transmission media, and the topology of the individual fieldbus.  In general, higher transmission speed decreases the segment length of bus oriented fieldbuses to a length in the range of 50 to 100 meters; low transmission speed allows a segment length in the range of a few kilometers. This flexibility in transmission speed is a big advantage against Ethernet based networks. Ethernet based fieldbuses are working with 100Mb/s or 1GB/s Ethernet media with a full packet size as defined by Ethernet. Pure sensor/actor networks of Ethernet based fieldbusses - like VARAN - are using a limited packet size of e.g. 128 bytes.

 

Fieldbuses with a ring topology like INTERBUS, EtherCAT, and SERCOS are working often with a physical extension in the range of kilometers because of the signal refreshing which is done by the fieldbus modules.  Fiber optical transmission medias allow in general extended segment lengths and increased noise immunity. The cable infrastructure of a fieldbus is much leaner than a comparable centralized point-to-point infrastructure. Our Fieldbus Comparison shows a collection of the most important fieldbuses,  their core attributes and their relationship to standards. Today fieldbuses are the core of every industrial distributed control and IO system. 

 

QNX & fieldbusses - 2 winning architectures!

The architecture of a fieldbus based distributed IO system is very similar to the distributed micro kernel architecture of QNX.  A fieldbus master can be considered as the kernel of a fieldbus based IO system, which communicates by messages with partner processes located in the connected remote fieldbus devices. Fieldbus devices with bus topology can be removed and added to the bus at run time as well as resource managers of the QNX operating system.

A fieldbus system looks like an architectural extension of the QNX architecture into the area of field IO devices!

The small interrupt latency of QNX provides the base for an optimal and secure handling of the individual fieldbus master controllers. This allows very small bus cycle durations with e.g. dumb CAN interface boards. The multi-core support of QNX provides the possibility for processing of complex fieldbus protocols by a dedicated core.  The reliability of QNX and fieldbus systems leads to very stable process control systems.

There are e.g. QNX based PROFIBUS-DP control systems at ground stations of the ESA which are running since more than 10 years without rebooting !

 

DACHS real-time solutions with fieldbuses are running worldwide for various kinds of reliable industrial automation applications, embedded systems, as well as in mission critical control systems.

 

 

STEINHOFF offers support packages for PC based control systems with fieldbuses running QNX 4.25 RTOS, QNX Neutrino RTOS v. 6.x , RTAI-Linux and Linux.  If you are interested in INTEGRITY or VxWorks based packages, please contact us. 

NEW in 2010: all DACHS products also for Real-Time-Linux with preemptive patch!