| Abstract |
In 2001 the author presented a paper at the GRC conference describing a state-of-the-art steamfield control system that utilized micro-PLCs for local geothermal steamfield control. A self-healing serial communications fiber optic ring network was used to allow the central plant control system to execute supervisory control over these distributed micro-PLCs via Modbus protocol using serial communications. In the intervening seven years, technology has evolved. Local process control with supervisory control from the DCS remains at the core of today’s system. However, we now recommend executing the local control logic in the final control element, typically a modulating control valve. The non-proprietary Foundation Fieldbus technology provides the best and only means readily available today to accomplish this goal. |