Hannover - May 2001

Distributed soft logic for drives tasks

Drive applications are amongst the most demanding in the control industry, typically requiring digital control sampling in the 0.5 to 5ms region. Traditionally, to achieve this level of performance, a PLC with a fast scan time and a high speed fieldbus would be employed. Increasingly, however, an alternative to this centralised approach is being employed - a distributed architecture where the overall system control is partitioned into individual programs on each drive (or node). The design goal is to eliminate the PLC, with all the application logic realised using IEC61131-3, distributed embedded soft logic.

In order to best leverage the facilities of its drives with their embedded soft logic, CT developed a fieldbus - CTNet - that would provide the necessary data throughput for highly dynamic applications. Using proven token ring data link technology, the CTNet protocol features an added protocol stack which provides dual cyclic data channels for efficient peer to peer to transfers of real time control data at rates of up to 5Mbits/sec.

Automation applications such as extruders, wire drawers, web process lines, winders and conveyor applications will benefit from this type of control.

For the operator interface, CT has a range of CTNet-enabled MMIs, whilst sister company Intellution has a CTNet driver for its FIX SCADA product.

C1: 'Distributed Softlogic' provides a more cost-effective, modular and flexible solution for distributed AC and servo drive control

• Control Techniques
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