News | December 3, 2003

Specifying a Control System

By Rob Lanham, General Manager, Ross Systems & Controls

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The business of creating an efficient mixing or blending system is a spectacular balancing act. The throughput you require must be balanced against batch size, agitator sizes, motor sizes, shear and tip speeds, viscosity, the thermal capacity of your product and heat-transfer media, energy costs, labor costs… and a hundred other variables.With so many equipment choices and tremendous competitive pressure to optimize performance, the mixing process itself has never been more complex. But in most cases today, the most challenging balancing act of all is still the specification of your process control equipment.

The process control system must balance your need for accuracy, consistency, flexibility and reliability against your need to control costs. This is why the control is now much more than the interface between the operator and the machine; it's a direct interface between your process system and your bottom line. Specify the process control equipment intelligently, and your production line will hum. Under-specify or over-specify the control system, and you're in for an avalanche of costs and delays.

Years ago, the control system and process control equipment were often little more than an afterthought assigned to a local contractor (who knew almost nothing about the process he was trying to control) and an overworked in-house engineer. Those days ended with the realization that the modern control is far more than a fancy digital version of an ON/OFF switch.

With the technology available today in sensors, integrated PID control logic, intelligent valves and central SCADA systems, every function in your processing system can be automated to operate at a terrific level of accuracy. But as accuracy increases, costs increase, too — and at an even faster rate. And this is where the most important balance of all becomes apparent: the balance between the accuracy that can be achieved and the accuracy needed.

Charles Ross and Son Company