Method of input signal resolution for actively redundant process control computers

A method of input signal resolution in a process control system having a plurality of actively redundant process control computers, where each of said actively redundant process control computers receives corresponding input signals which represent analog values from a physical process being controlled with each process control cycle, comprising the steps of:

• mutually exchanging at least one block of said corresponding input signals between each of said actively redundant process control computers;
• determining if a predefined tolerance has been exceeded between the analog values of at least some of said corresponding input signals, and if said predefined tolerance was exceeded during the present process control cycle, then determining if said predefined tolerance was also exceeded in at least the last process control cycle;
• individually selecting an analog input value at each of said actively redundant process control computers for each of said input signals exchanged where said predefined tolerance was not exceeded in the present process control cycle;
• employing the analog input value selected in the last process control cycle to decide process control outputs in the present process control cycle where said predefined tolerance was exceeded during the present process control cycle, but not the immediately prior process control cycle;
• and
• using a predetermined magnitude criteria to individually select an analog input value at each of said actively redundant process control computers when it has been determined that said predefined tolerance was exceeded for the present process control cycle and at least the last process control cycle;
• wherein each of said corresponding input signals is provided with its own predetermined magnitude criteria which includes at least one bit to alternatively represent a select-high and a select-low basis for selecting the analog input value.

A method of input signal resolution in a process control system having a plurality of actively redundant process control computers, where each of said actively redundant process control computers receives corresponding input signals which represent analog values from a physical process being controlled with each process control cycle, comprising the steps of:

• mutually exchanging at least one block of said corresponding input signals between each of said actively redundant process control computers;
• determining if a predefined tolerance has been exceeded between the analog values of at least some of said corresponding input signals, and if said predefined tolerance was exceeded during the present process control cycle, then determining if said predefined tolerance was also exceeded in at least the last process control cycle;
• individually selecting an analog input value at each of said actively redundant process control computers for each of said input signals exchanged where said predefined tolerance was not exceeded in the present process control cycle;
• and
• employing the analog input value selected in the last process control cycle to decide process control outputs in the present process control cycle where said predefined tolerance was exceeded during the process control cycle, but not the immediately prior process control cycle;
• wherein a plurality of blocks of said corresponding input signals are mutually exchanged between each of said actively redundant process control computers, and each of said blocks of corresponding input signals includes at least one word which represents the validity of the input signals contained in said block and wherein said mutual exchange step includes the steps of determining a validity indicator from said block of corresponding input signals as received, and comparing said determined validity indicator with the validity indicator that was received with a block of corresponding input signals to determine the validity of said mutual exchange step.

A method of input signal resolution in a process control system having a plurality of actively redundant process control computers, and at least one triply redundant computer unit which selects an analog input value from at least one set of corresponding analog input signals by at least two of three computers contained in said triply redundant computer unit;

• comprising the steps of:
• transmitting said input value selected from each of said two computers contained in said triply redundant computer unit to at least one of said actively redundant process control computers;
• determining if a predefined tolerance has been exceeded between the analog values of said transmitted signals at each of said actively redundant process control computers;
• using a predetermined magnitude criteria to individually select the analog input value to be employed in process control decisions at each of said actively redundant process control computers when it has been determined that said predefined tolerance was exceeded;
• wherein each of said corresponding analog input signals is provided with its own predetermined magnitude criteria;
• and
• wherein said predetermined magnitude criteria includes at least one bit to alternatively represent a select-high and a select-low basis for selecting the analog input value.