Electrical viscometer

Claim 1

AN ELECTRICAL VISCOMETER COMPRISING AN ELECTRIC MOTOR, A DRAG MEMBER ADAPTED TO BE DRIVEN BY SAID MOTOR THROUGH VISCOUS LIQUID UNDER TEST, MEANS FOR DERIVING A FINAL SIGNAL FROM THE INPUT CURRENT TO SAID MOTOR, AND MEANS TO COMPENSATE THE FINAL SIGNAL, AT ANY VALUE THEREOF, FOR ERRORS THEREIN DUE TO VARIATION IN THE FREQUENCY OF AN ALTERNATING CURRENT VOLTAGE SUPPLY TO THE VISCOMETER AND COMPRISING, IN COMBINATION, A RESONANT CIRCUIT DERIVED FROM SAID VOLTAGE SUPPLY AND TURNED TO A FREQUENCY AT LEAST SLIGHTLY OUTSIDE THE BANDWIDTH WITHIN WHICH FREQUENCY VARIATIONS ARE LIKELY TO BE CONFINED, MEANS RECTIFYING THE VOLTAGE OUTPUT FROM THE RESONANT CIRCUIT; A SECOND CIRCUIT ALSO DERIVED FROM SAID VOLTAGE SUPPLY, SAID SECOND CIRCUIT BEING NON-REACTIVE AND INCLUDING A NON-REACTIVE LOAD, THE SECOND CIRCUIT OUTPUT BEING THUS INDEPENDENT OF FREQUENCY VARIATIONS, MEANS RECTIFYING THE VOLTAGE OUTPUT FROM THE SECOND CIRCUIT; MEANS CONNECTING THE VOLTAGE OUTPUTS FROM THE RESONANT AND SECOND CIRCUITS IN OPPOSITION ONE TO THE OTHER TO GIVE A RESULTANT COMPENSATING VOLTAGE; MEANS FEEDING SAID RESULTANT COMPENSATING VOLTAGE TO THE FINAL SIGNAL FOR COMPENSATION THEREOF WHEN THE FREQUENCY VARIES FROM ITS STANDARD VALUE, MEANS FOR CAUSING SAID RESULTANT VOLTAGE TO INFLUENCE THE FINAL SIGNAL IN A POSITIVE OR NEGATIVE DIRECTION DEPENDING ON WHICH SIDE OF THE STANDARD FREQUENCY THE FREQUENCY VARIATION HAS OCCURED, AND MEANS FOR MEASURING THE FREQUENCY-COMPENSATED FINAL SIGNAL.