Redundant input reliability check for programmed multi-channel position control

Claim 1

IN A PROGRAM CONTROLLED SYSTEM FOR CONTROLLING MEASURE HAVING A AND B CHANNELS FOR CONTROLLING MEASURES A AND B RESPECTIVELY, EACH CHANNEL INCLUDING MEANS FOR READING RECORD MEDIA HAVING STORED COMMAND DATA REPRESENTING A DESIRED MEASURE, A COMPARTOR WHICH COMPARES A REPRESENTATION OF THE DESIRED MEASURE AND A REPRESENTATION OF THE ACTUAL MEASURE AND IN RESPONSE TO DISAGREEMENT BETWEEN DESIRED AND ACTUAL MEASURES PROVIDES AN ERROR OUTPUT INDICATIVE OF THE DISAGREEMENT, COUPLING MEANS RESPONSIVE TO SAID READING MEANS FOR SUPPLYING REPRESENTATION OF COMMAND DATA TO SAID COMPARATOR, AND MEANS FOR SUPPLYING REPRESENTATION OF SAID ACTUAL MEASURE TO SAID COMPARATOR, THE COMBINATION THEREWITH OF MEANS FOR CHECKING THE RELIABILITY OF SAID SYSTEM COMPRISING SWITCH MEANS FOR INTERCHANGING SAID READING MEANS AND SAID COUPLING MEANS WHEREBY THE A READING MEANS AND THE A COUPLING MEANS SUPPLY REPRESENTATION OF COMMAND DATA TO THE B COMPARATOR AND THE B READING MEANS AND THE B COUPLING MEANS SUPPLY REPRESENTATION OF COMMAND DATA TO THE A COMPARATOR, AND MEANS FOR FEEDING A DUPLICATE OF AN ORIGINAL A AND B COMMAND TO SAID READING MEANS IN REVERSE ORDER WHEREBY THE A READING MEANS READS THE B COMMAND AND THE B READING MEANS READS THE A COMMAND, AND MEANS RESPONSIVE TO THE RELATION BETWEEN THE ERROR OUTPUTS RESULTING FROM THE ORIGINAL AND DUPLICATE COMMANDS.