Abstract: A noncontact thickness gauge system for measuring the thickness of a material is disclosed which includes a source of penetrating radiation, a radiation detector for detecting the amount of radiation received from the radiation source where the level of received radiation is a function of the radiation absorption characteristics and thickness of the material located in the radiation path, a memory for storing the output signals of the detector and curve-defining parameters for a plurality of calibration curves which correspond to respective ranges of thickness values, and a processor for processing the various signals and curve-defining parameters to determine the thickness of the material in the radiation path. The calibration curves are quadratic and are defined by at least three calibration points.

Abstract: In a radiation thickness gauge of the type wherein the thickness of a sample is determined by measuring the amount of radiations transmitting through the sample, there is provided an x-ray generator for transmitting a radiation flux through a reference sheet utilized for calibration purposes and having a thickness manifesting a radiation absorption which is equivalent to that of the sample having a nominal thickness which has been compensated for the difference in the radiation absorption characteristics of the reference sheet and the sample, a radiation detector for detecting the amount of the radiations transmitting through the reference sheet and the sample, a memory for storing the output of the detector when the reference sheet is interposed, and an operator, such as a computer.