Non-destructive thickness measuring device

Claim 1

A DEVICE FOR MEASURING THE THICKNESS OF A SPECIMEN HAVING AT LEAST ONE EXPOSED SURFACE, COMPRISING: A PULSE GENERATOR; A TRANSDUCER FOR CONVERTING ELECTRICAL PULSES FROM THE PULSE GENERATOR TO ULTRASONIC PULSES AND FOR CONVERTING REFLECTED ULTRASONIC PULSES TO ELECTRICAL PULSES; A LIQUID COLUMN COUPLING THE TRANSDUCER TO THE EXPOSED SURFACE OF THE SPECIMEN; A DIGITAL COUNTER RESPONSIVE TO SUCCESSIVE PULSES FOR COUNTING THE NUMBER OF SUCH PULSES; SIGNAL GENERATOR MEANS FOR PRODUCING A WAVE TRAIN OF SUCCESSIVE PULSES; GATE MEANS CONNECTING SAID SIGNAL GENERATOR MEANS TO SAID DIGITAL COUNTER FOR CONTROLLING THE TIME DURING WHICH SUCCESSIVE PULSES ARE TRANSMITTED FROM SAID SIGNAL GENERATOR MEANS TO SAID DIGITAL COUNTER; A RECEIVER; AN AND GATE CONNECTING THE TRANSDUCER TO THE RECEIVER; AND MEANS CONNECTED TO THE PULSE GENERATOR AND THE AND GATE FOR CLOSING THE AND GATE UNTIL AFTER THE OCCURRENCE OF THE ELECTRICAL PULSE PRODUCED BY THE TRANSDUCER IN RESPONSE TO THE ULTRASONIC PULSE REFLECTED FROM THE EXPOSED SURFACE OF THE SPECIMEN THROUGH SAID LIQUID COLUMN; AND CONTROL CIRCUIT MEANS CONNECTED TO SAID GATE MEANS AND TO SAID RECEIVER FOR OPENING SAID GATE MEANS ONLY DURING THE TIME INTERVAL BETWEEN A PAIR OF SELECTED, SUCCESSIVE REFLECTED PULSES, WHEREBY SAID COUNTER MEASURES TWICE THE TRAVEL TIME OF AN ULTRASONIC PULSE THROUGH THE SPECIMEN, THEREBY INDICATING THE THICKNESS OF THE SPECIMEN.