The Dow Chemical Company

Donald J Grinwis

Wayne P Dupree

Timothy J Grai

Robert S Hoy

Oscar E Schulze

Robert S Glaser

G Paul Fernandez

Johannes C Kanse

Robert J Hozeska

Eloy Baca, Jr

Douglas P Pelletier

A process control interface system having a network of distributed triply redundant input/output field computer units. The system includes a plurality of self-contained remotely located triply redundant field computer units connected to decision making redundant process control computers through a bi-directional communication network having at least two concurrently active communication channels. Each of the field computer units include a set of at least redundant field computers for arbitrating both input and output signals. The input arbitration method enables a plurality of selectable default input conditions, such as select HIGH and select LOW, in the event that a majority agreement cannot be reached among valid input signals. The output arbitration method includes a plurality of selectable default output conditions, such as fail SAFE and fail LAST. Each of the default input and output conditions may be rapidly adjusted through software selection. The field computer units also include individual abort circuits for each output signal to be transmitted to a device which affects the operation of the physical process. These abort circuits effectively enforce the output value signals arbitrated independently through each of the three redundant field computers using a voting procedure.

Process control interface system having triply redundant remote field

A method of input signal resolution in a process control system where each of the actively redundant process control computers performs a common arbitration process on corresponding input signals. Blocks of corresponding input signals are mutually exchanged by the actively redundant process control computers, and an initial check is made to determine if these input signals are valid. For input signals representing valid analog values, a determination is made as to whether a predefined tolerance has been exceeded between corresponding input signals in the present process control cycle. When the predefined tolerance has been exceeded, then a check will be made to determine the predefined tolerance was also exceeded in the last process control cycle. If the predefined tolerance was not exceeded in the last process control cycle, then the analog input value selected during the last process control cycle will be employed in the present process control cycle. If the predefined tolerance was exceeded in both the present and the last process control cycle, then a predetermined magnitude criteria will be used to select the analog input value for use in making process control decisions. An indication will also be provided in each of the actively redundant process control computers to identify which of the corresponding input signals were selected by that process control computer.

Method of input signal resolution for actively redundant process control

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Midland, MI, United States of America

Donald J Grinwis