Radiation thickness gauge including a feedback readout circuit

Claim 1

A RADIATION GAUGE FOR MEASURING AND PROVIDING AN OUTPUT INDICATION OF THE THICKNESS OF A PROCESS MATERIAL SHEET COMPRISING: A RADIOACTIVE SOURCE EMITTING A BEAM OF RADIATION INCIDENT UPON ONE SIDE OF SAID PROCESS MATERIAL SHEET; A RADIATION DETECTOR DISPOSED ON THE OPPOSITE SIDE OF SAID MATERIAL SHEET FROM SAID RADIATION SOURCE AND PROVIDING AN OUTPUT SIGNAL CURRENT VARYING IN ACCORDANCE WITH VARIATIONS IN THE QUANTITY OF RADIATION INCIDENT UPON SAID DETECTOR; A SIGNAL RESISTOR COUPLED ACROSS SAID DETECTOR, THE VOLTAGE DEVELOPED ACROSS SAID SIGNAL RESISTOR BEING DIRECTLY PROPORTIONAL TO SAID OUTPUT SIGNAL CURRENT; AN AMPLIFIER HAVING FIRST AND SECOND INPUT TERMINALS, SAID FIRST INPUT TERMINAL BEING CONNECTED TO ONE END OF SAID SIGNAL RESISTOR, SAID AMPLIFIER PROVIDING AS AN OUTPUT A SIGNAL HAVING AN AMPLITUDE DIRECTLY RELATED TO THE VALUE OF THE VOLTAGE CONNECTED ACROSS SAID FIRST AND SAID SECOND INTUT TERMINALS; A LOAD RESISTOR CONNECTED BETWEEN THE OUTPUT OF SAID AMPLIFIER AND THE OTHER END OF SAID SIGNAL RESISTOR, SAID LOAD RESISTOR HAVING A FIXED TAP CONNECTED TO IT AND A VARIABLE TAP CONNECTED TO IT, SAID FIXED TAP BEING CONNECTD ALSO TO SAID SECOND INPUT TERMINAL OF SAID AMPLIFIER THEREBY PROVIDING A SERIAL COMBINATION OF SAID SIGNAL RESISTOR AND A PORTION OF SAID OUTPUT RESISTOR ACROSS SAID AMPLIFIER INPUT TERMINALS; A VOLTAGE SOURCE; A POTENTIOMETER CONNECTED ACROSS SAID VOLTAGE SOURCE, ONE END OF SAID POTENTIOMETER BEING CONNECTED TO THE JUNCTION BETWEEN SAID SIGNAL RESISTOR AND SAID LOAD RESISTOR; A VOLTAGE MEASURING AND INDICATING DEVICE CONNECTED BETWEEN THE VARIABLE ARM OF SAID POTENTIOMETER AND THE SAID VARIABLE TAP OF SAID LOAD RESISTOR, SAID VARIABLE ARM BEING POSITIONED ON SAID POTENTIOMETER TO PROUDCE A PREDETERMINED VOLTAGE ACROSS SAID VOLTAGE MEASURING MEANS FOR A PREDETERMINED POSITION OF SAID VARIABLE TAP AT A PREDETERMINED THICKNESS OF SAID PROCESS MATERIAL SHEET.