Liquid level indicator

Claim 1

LIQUID LEVEL SENSING APPARATUS WHICH COMPRISES A MAGNETOSTRICTIVE TRANSDUCER HAVING A DIAPHRAGN AND AN ELONGATED MAGNETOSTRICTIVE ELEMENT ATTACHED THERETO FOR PRODUCING OSCILLATION THEREOF, SAID DIAPHRAGM BEING EXTERNALLY POSITIONED FOR CONTACT BY A LIQUID WHOSE LEVEL IS TO BE SENSED AND BE DAMPED THEREBY, SAID DIAPHRAGM AND THE STRUCTURE ATTACHED THERETO FORMING A MECHANICALLY RESONANT STRUCTURE, SEPARATE TRANSMITTING AND RECEIVING COILS, ENCIRCLING SAID MAGNETIOSTRICTIVE ELEMENT IN SPACED RELATIONSHIP THEREALONG FOR PRODUCING AND RESPONDING TO OSCILAATIONS THEREIN, RESPECTIVELY, A MAGNET ENCIRCLING THE MAGNETOSTRICTIVE ELEMENT FCOR PRODUCING A SUBSTANTIAL MAGNETIC BIAS THEREIN, AN AMPLIFIER HAVING AN INPUT CONNECTED TO THE RECEIVING COIL AND AN OUTPUT CONNECTED TO THE TRANSMITTING COIL IN REGENERATIVE RELATIONSHIP TO FORM A REGENERATIVE LOOP INCLUDING SAID MAGNETOSTRICTIVE ELEMENT IN WHICH THE NEGENERATIVE FREQUENCY OF OSCILLATION IS ESSENTIALLY DETERMINED BY THE MECHANICAL RESONANT FREQUENCY OF SAID MECHANICALLY RESONANT STRUCTURE, THE GAIN OF THE AMPLIFIER BEING PREDETERMINED TO LIE BETWEEN THE GAINS REQUIRED TO PRODUCE OSCILLATION OF SAID DIAPHRAGM WHEN IN CONTACT WITH AND OUT OF CONTACT WITH THE LIQUID, SHIELDING MEANS IN SAID TRANSDUCER FOR REDUCING THE ELECTROMAGNETIC COUPLING BETWEEN SAID COILS TO A VALUE SUBSTANTIALLY LESS THAN THE COUPLING THEREBETWEEN THROUGH THE MAGNETOSTRICTIVE ELEMENT WHEN THE DIAPHRAGM IS IN CONTACT WITH SAID LIQUID, MEANS FOR DETERMINING THE PRESENCE OR ABSENCE OF OSCILLATIONS IN SAID REGENERATIVE LOOP.