Electrical measuring apparatus

Claim 1

IN A GRAPHIC RECORDER OF THE STRIP CHART VARIETY, MEANS FOR RECEIVING AN UNKNOWN VOLTAGE THAT IS TO BE MEASURE, MEANS FOR MOVING A GRAPH PAPER ACROSS A FLAT SURFACE OF SAID RECORDER, A HOLD-DOWN CLAMP MEANS FOR SECURING SAID PAPER TO SAID RECORDER SURFACE, SAID HOLDDOWN CLAMP MEANS INCLUDING A FLAT MEMBER DISPOSED TO BEAR AGAINST SAID PAPER, A PLURALITY OF RODS EXTENDING FROM SAID FLAT MEMBER EACH PROTRUDING THROUGH A HOLE IN SAID FLAT SURFACE, SAID PLURALITY OF RODS EACH HAVING A SEATING COLLAR FIXED ADJACENT SAID FLAT MEMBER, ANOTHER SUPPORTING COLLAR FIXED TO ITS END AND A COMPRESSION SPRING DISPOSED BETWEEN AND EXERTING A FORCE UPON SAID SUPPORTING COLLAR AND THE UNDERSIDE OF SAID FLAT SURFACE, A PEN FOR RECORDING A CURVE ON SAID PAPER WHICH CURVE IS REPRESENTATIVE OF THE VALUE OF SAID UNKNOWN VOLTAGE, MEANS FOR GENERATING A REFERENCE VOLTAGE REPRESENTATIVE OF THE POSITION OF SAID PEN UPON SAID PAPER, CHOPPER MEANS FOR COMPARING SAID UNKNOWN VOLTAGE TO SAID REFERENCE VOLTAGE TO GENERATE AN A.C. SIGNAL AT A GIVEN FREQUENCY, AMPLIFIER MEANS FOR AMPLIFYING SAID A.C. SIGNAL, A SERVO-MOTOR HAVING ONE PHASE WINDING ENERGIZED BY AN A.C. POWER SUPPLY OF SAID GIVEN FREQUENCY AND HAVING ANOTHER PHASE WINDING ENERGIZED BY SAID AMPLIFIED A.C. SIGNAL, MEANS ON SAID AMPLIFIER MEANS FOR CHANGING THE GAIN OF SAID AMPLIFIER, SAID MEANS FOR GENERATING A REFERENCE VOLTAGE COMPRISING A POTENTIOMETER HAVING A MOVABLE PICK-OFF ARM MOVABLE BY SAID SERVO-MOTOR, A VOLTAGE REFERENCE RESISTOR CONNECTED IN SERIES WITH SAID PICK-OFF ARM AND AN ANTI-HUNTING NETWORK ACROSS WHICH SAID REFERENCE VOLTAGE IS GENERATED, AND MEANS FOR OBTAINING VARIOUS RANGES OF VOLTAGE DROP FROM SAID VOLTAGE REFERENCE RESISTOR AS SAID PICK-OFF ARM MOVES BETWEEN EXTREME POSITIONS ON SAID POTENTIOMETER.