Comparator mechanism

Claim 1

AN ELECTRICAL CONTROLLER FOR MAINTAINING THE ACTUAL VALUE OF A PROCESS VARIABLE SUBSTANTIALLY AT A SELECTED VALUE, SAID CONTROLLER INCLUDING TRANSDUCING MEANS FOR PROVIDING AN OUTPUT ERROR SIGNAL THAT VARIES IN AMPLITUDE AND PHASE IN ACCORDANCE WITH THE INSTANTANEOUS DIFFERENCE BETWEEN SAID SELECTED AND ACTUAL VALUES OF SAID PROCESS VARIABLE, AND MEANS INCLUDING A SERVO SYSTEM RESPONSIVE TO SAID OUTPUT ERROR SIGNAL FOR VARYING SAID PROCESS VARIABLE THEREBY TO REDUCE SAID ERROR SIGNAL TO ZERO, SAID TRANSDUCING MEANS INCLUDING SENSING MEANS RESPONSIVE TO SAID PROCESS VARIABLE FOR SENSING ITS ACTUAL VALUE, MEANS RESPONSIVE TO SAID SENSING MEANS FOR PROVIDING A MECHANICAL OUTPUT SIGNAL WHOSE AMPLITUDE VARIES AS A FUNCTION OF THE ACTUAL VALUE OF SAID PROCESS VARIABLE, AN ELECTRICAL DIVIDER ELEMENT HAVING A CONTINUOUSLY VARIABLE TAP, ADJUSTING MEANS MECHANICALLY CONNECTED TO SAID DIVIDER ELEMENT FOR POSITIONING SAID DIVIDER ELEMENT WITH RESPECT TO SAID TAP, THEREBY TO ESTABLISH SAID SELECTED VALUE OF SAID PROCESS VARIABLE, ADJUSTABLE LINKAGE MEANS COUPLED TO SAID SENSING MEANS AND RESPONSIVE TO SAID MECHANICAL OUTPUT SIGNAL FOR VARYING THE POSITION OF SAID TAP ONLY OVER A PREDETERMINED PORTION OF THE RANGE OF MOTION OF SAID ELECTRICAL DIVIDER ELEMENT, WHEREBY THE AMPLITUDE AND PHASE OF SAID OUTPUT ERROR SIGNAL ARE SUBSTANTIALLY ALWAYS PROPORTIONAL TO SAID INSTANTANEOUS DIFFERENCE BETWEEN THE ACTUAL AND SELECTED VALUES OF SAID PROCESS VARIABLE.