Patent GB-768943-A (GB)
Title: Improvements relating to methods of and devices for inspecting containers
Inventor: GOLDSMITH KURT
IPC: B65B1/48
Filed: 1953-07-30
Abstract: 768,943. Inspection of containers by ionizing radiation. UNILEVER, Ltd. July 23, 1954 [July 30, 1953], No. 21210/53. Class 40 (3). In a method of inspecting containers comprising passing them through one or more beams of penetrating ionizing radiation whereby to attenuate the radiation received by a radiation detector to the output of which a control means responds, a first output condition of the means is produced when the intensity of radiation incident on the detector has a fixed reference value and a second output condition when the intensity has one of two values respectively above and below the reference value. In one embodiment 2.2 Mev # rays from a source 1 of Sr/Yt 90 are formed by a collimator 3<1> into two narrow parallel beams A, B which are projected across the path of containers 5 carried on a conveyer 2 at heights respectively just above and just below the desired filling level of the containers on to ionization chamber 4. The beams are of such intensity that the walls of the container alone reduce it by 50 per cent, while the wall plus contents completely block it. A compensating beam of equal intensity from the same or from a similar source is directed on to a second ionization chamber 8 through a screen with absorbing power equivalent to that of an empty tin. The chambers 4, 8 with resistors 12, 14 form the arms of a bridge. When the bridge is balanced, i.e. when an empty or underfilled container intercepts the # ray beams electrometer tetrodes 13, 15 take equal currents so that identical potentials are applied to the grids of triodes 26, 27, the anodes of which are connected through relay 30 having contacts 31 which are open when the relay is operative. Only when the anode currents of valves 26, 27 are balanced, that is when an empty or underfilled can intercepts the beams, does the relay fall out to close the circuit from a source of voltage to an alarm, indicator or ejector 10. The anode voltages of valves 13, 15 are also applied to grids of further triodes 28, 29 respectively, the anodes of which are connected through a relay 32 in series with rectifier 34. These triodes are so biased that only when containers which are overfull and therefore block both beams does the anode voltage of 29 exceed that of 28 to energize relay 32 the contacts 33 of which close the alarm &c. circuit. In all other circumstances the anode potentials are either the same or that of valve 28 is the greater so that the relay 32 remains unenergized. The alarm indicator, or ejector circuit, is therefore completed when the containers are empty or underfilled via contact 31 and when they are overfilled via contact 33. If the anode or heater supply of the aforesaid valves fails the safety relay 23 in the anode circuit of a pentode 24 deriving its supplies from the same source is deenergized to open circuit the ejector 10 via its contacts 22. In a further embodiment required to reject only empty or underfilled containers a single beam projected across the path of the tins just below the filling level replaces the two beams and the valves 28 and 29 and relay 32 are omitted from the circuit.