Measuring apparatus

Claim 1

LIQUID LEVEL SENSING MEANS COMPRISING AN ELONGATED PROBE MEMBER HAVING THEREIN A CONCENTRIC ARRAY OF LONGITUDINAL PASSAGES, A CENTRAL ONE OF SAID PASSAGES COMPRISING A RECEIVING PASSAGE AND A PLURALITY OF PASSAGES IN SPACED ARRAY ABOUT SAID RECEIVING PASAGE COMPRISING A PLURALITY OF TRANSMITTING PASSAGES, SAID TRANSMITTING PASSAGES AND SAID RECEIVING PASSAGE BEING OPEN TO ONE END OF SAID PROBE, MEANS CONNECTED TO SAID TRANSMITTING PASSAGES FOR PRODUCING A UNIFORM STREAM OF AIR ISSUING FROM SAID OPEN END OF SAID TRANSMITTING PASSAGE TOWARD THE SURFACE OF SAID LIQUID, SAID RECEIVING PASSAGE BEING RESPONSIVE TO A PORTION OF SAID STREAM OF AIR REFLECTED FROM SAID SURFACE TO PRODUCE A PRESSURE WITHIN SAID RECEIVING PASSAGE PROPORTIONAL TO THE PROXIMITY OF SAID PROBE END TO SAID SURFACE OF SAID LIQUID, SERVO MOTOR MEANS CONNECTED TO SAID PROBE FOR POSITIONING SAID PROBE RELATIVE TO THE SURFACE OF SAID LIQUID, PRESSURE RESPONSIVE MEANS COUPLED TO SAID RECEIVING PASSAG FOR PRODUCING A CONTROL SIGNAL REPRESENTATIVE OF THE PRESSURE PRODUCED IN SAID RECEIVING PASSAGE MEANS RESPONSIVE TO SAID CONTROL SIGNAL FOR CONTROLLING THE OPERATION OF SAID SERVO MOTOR MEANS TO POSITIONING SAID PROBE AT A POSITION OF EQUILIBRIUM A PREDETERMINED DISTANCE ABOVE THE SURFACE OF SAID LIQUID, AND POSITION DETECTOR MEANS CONNECTED TO SAID PROBE TO PRODUCE AN OUTPUT SIGNAL REPRESENTATIVE OF THE POSITION OF SAID PROBE, THEREFORE, OF THE LEVEL OF THE SURFACE OF SAID LIQUID.