Q: when is a DCS not a DCS?/A: when it isn't a PLC either
15 Jan 2000
Such enigmatic questions were posed by last month's launch by Mitsubishi Electric (enter 360 on enquiry card) of its `Q' series of control systems aimed at the continuous process markets.
Designed to bridge the gap between PLCs and DCSs, the Q series is said to combine the advantages of processing discrete I/O with ladder logic PLC-type controllers, and the superior handling of the analogue I/O and closed-loop control familiar to DCS users - but without the high costs of the distributed control solutions.
Although the Q series is fully compatible with Mitsubishi's existing PLC units, its most significant development, says Q products manager David Folley, is the use of redundant systems components. Users can implement dual redundancy systems wherever the process requires and to whatever level of resilience is needed.
The Q4ARCPU processor is Mitsubishi's first product to offer fail-safe operation in this way. One processor provides a hot processing unit for control, while a replica standby can be instantly switched into the control bus should the `hot' unit develop a fault.
To meet the demand for ever-more powerful control systems, the Q series features a 32bit RISC-based processor and coprocessors for floating point maths and the PID control that is an essential part of any DCS system.
