GB699081A - Improvements in or relating to radiation level indicating circuits for use in conjunction with a radioactive source - Google Patents

Abstract

699,081. Control circuits utilizing radiation. NATIONAL RESEARCH DEVELOPMENT CORPORATION. June 13, 1951 [June 13, 1950], No. 14691/50. Class 40 (iii). [Also in Group XL (c)] A circuit for use in the automatic filling of cartons in which the filled cartons pass on a belt in a continuous sequence between a radioactive source and a Geiger-Muller counter tube comprises a relay circuit as shown in the Figure. Relay contacts 18 are operated when the rate of pulses produced from the self-quenching Geiger- Muller counter 12, 13 exceeds a predetermined value. The electrode 13 of the counter is energized from the A.C. supply across terminals 9 via the voltage multiplier network 14. Halfwave rectified A.C. is derived from rectifier 6 and applied across the cold-cathode gas-filled tube 1 which fires when a pulse on the counter electrode 12 coincides with peak supply voltage across it. The current flow through the tube 1 is averaged by the integrating network 4, 5 and relay coil 3 is energized to operate contacts 18 if the pulse repetition rate exceeds a given value. An unfilled or partly-filled carton allows radiation to fall on the counter at such a rate that the relay operates to sound an alarm. In a modification a photo-electric cell is also illuminated from a light source passing across the conveyer belt so that if there is a discontinuity in the sequence of cartons passing along the belt the trigger electrode of the tube 1 is held negative to prevent operation of the relay. In a further modification, Fig. 2 (not shown), for use with a non-self-quenching G.M. counter tube the tube is quenched by reducing the supply voltage across it once per cycle. Specification 699,129 is referred to.