GB692609A - Improvements in the thickness measurement of thin sheets and the like by -a-rays - Google Patents

Abstract

692,609. Measuring thickness by radioactivity. BERTHOLD, R. March 10, 1952 [March 10, 1951], No. 6226/52. Class 40 (iii). In measuring thickness by means of Beta rays a natural source of high intensity is used, sensitivity being maintained by substantially balancing the ionization current, only the small unbalance being indicated. As shown, Beta rays from one of the natural sources 1a, 1b, 1c, any one of which may be uncovered by movement of a plate 15, pass through a moving web 2 under test to an ionization chamber 3. The voltage developed by the ionization current across the anode-cathode space of a triode 17 is balanced by the current through a balancing chamber of a triode 17 is balanced by the chamber 3a receiving radiation from a source 1d through a plate 2a. Thus only variation of its thickness of the material 2 from a setting determined by the balancing chamber is indicated by the meter 11. The triode is mounted in a metal housing mechanically united with the ionization chambers. In the arrangement of Fig. 1 (not shown), the ionization current produces a voltage in a part of a slide wire through which a steady current is maintained by an auxiliary voltage source. The slider is adjusted until a combined meter and amplifier indicate balance when the slider position is a measure of thickness. In the embodiment of Fig. 2 (not shown), a central radiation source directs Beta rays through the test material on one side and a standard on the other to two ionization chambers the currents of which flow through a common load resistor, unbalance being indicated by an amplifier and meter connected across the resistor.