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A fault tolerant control and sensor network with predictable real time QoS

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1 Author(s)

A field bus architecture particularly designed for control and sensor applications in industrial automation with high real time and fault tolerance requirements is presented, which not only allows to determine the runtime performance a priori, but also to control it during the entire process duration. Basically, it consists of a dual ring bus, on both its channels telegrams are redundantly transmitted in opposite directions, thus making delay measurements feasible. A GPS-fed, high accuracy ASIC timer module is used for time synchronisation. Only one GPS receiver is required per system, because the bus nodes' timers are synchronised via the field bus by an integrated time measurement procedure. Furthermore, alarm jobs can be handled by the ASIC with highly precise UTC in all units of a distributed system. Security of telegram transfers is achieved by a Hamming encoding, which allows to detect or to correct predeterminable numbers of errors In the data bits, respectively. Here, three protection bits are provided for any four data bits, i.e., for any nibble. In contrast to the prevailing method, viz., that data repetition is requested when an error is recognised, the time required for a corrective action based on Hamming encoding is predictable. Additionally, the transfer of short data nibbles provides the high flexibility needed to deal with different peripheral equipment. Even in the presence of strong disturbances on the transmission channel, the two-way signal coding by a modified "frequency shift keying" method and decoding by the Goertzel algorithm enables the receivers to recognise the input signals securely In the course of communication, transmitting and receiving modules exchange data and synchronisation characters, which are clearly distinguished by their respective signal encodings. This distinction simplifies identification, and facilitates safe recognition of the two signals. Furthermore, this kind of communication reduces the number of synchronisation characters required.

Published in:

AFRICON, 2004. 7th AFRICON Conference in Africa  (Volume:2 )

Date of Conference:

15-17 Sept. 2004