WIDE-RANGE RADIATION GAGE FOR DETERMINING A MATERIAL PROPERTY

摘要

Photon radiation from a high energy nuclear source is beamed through a test material to gage a material property such as hot steel plate thickness which may be subject to temperature variation during gaging and grade variations from plate-to-plate. Emerging radiation strikes a scintillation detector having a self-balancing measuring loop, the latter consisting of a photodetector having a controlled-gain photomultiplier (PM) tube optically coupled to a scintillator and serially connected with a comparator-integrator which developes an error voltage and a variable dynode voltage source for the PM tube which is controlled by the error voltage. Gage operation is based on the phenomena of a nonlinear PM tube gain characteristic being inverse and nearly equal to a nonlinear radiation absorption characteristic of the test material. Thus, when emerging radiation varies in relation to the material property, it causes the error voltage to vary the dynode voltage which in turn controls tube gain in a manner to maintain anode current constant over a single wide range of material property gaging, even during radiation source decay and PM tube drift. Consequently, the dynode voltage varies slightly nonlinearly as a function of the test material property being gaged. The dynode voltage is also fed to a manual zero and attenuation comparator and then to a stepless linearizer for correcting the slight nonlinearity of a fraction of the dynode voltage. A compensator, operating under control of a data source and a pyrometer, modifies the linearized gaging signal to correct for effects thereon caused by material grade and temperature variations. The linearized and compensated gaging signal is fed through one input of a differential output amplifier to a digital gaging indicator, as well as to a gaging deviation profile meter, thereby providing readings corrected to what the material will gage when cooled to a room temperature. An automatic zero circuit, which consists of a switched integrator controlled by a test material detector, operates on the other input of the differential output amplifier to maintain the output of said amplifier at zero when there is no test material being gaged. Additional circuits provided in the gage enable profiling of the test material as well as calibrating the gage both mechanically and electrically.