Patent GB-835991-A (GB)
Title: Improvements relating to chemical balances
IPC: G01G1/00
Filed: 1955-04-22
Abstract: 835,991. Ionizing gases by radio-activity. WHITCROFT, R. J., and MONK, L. H. June 13, 1956 [April 22, 1955], No. 11718/55. Class 98(1) [Also in Group XVIII] A radio active source is arranged in a balanced case, with means controllable by opening a door of the case for screening at least part of the interior from the source. In one form, the source of radiation is fixed on the inside of the vertically sliding front door of a balanced case. When the door is closed the source radiates inwards, but when the door is raised the source is moved behind a screen which masks the radiation. The screen may consist of the glass partition separating the main part of the case from the beam chamber. The source of radiation is a radio-active isotope, e.g. tellurium 204, which gives mainly beta radiations and which may be in the form of a disc. The radiation provides sufficient ionization to prevent static charges from forming on the insulated parts of the balance, but is screened by about 2 millimetres of glass or denser material. As shown in Fig. 1, the radiation source is mounted in a circular metal block 5 and is screened by a flap 6 secured to an arm 7. A rod 8 secured to the arm 7 is journalled in bearings 9 mounted on the upper part of the block 5. A lever 10 loosely mounted on the rod 8 and retained thereon by a collar 11 rests, in the position shown, on a pin 12 extending from the collar 11. When the door 1 of the balance case is lowered, a plate 15 mounted thereon engages the lever 10 pressing it down to raise the flap 6 to uncover the radio-active source. Whenever the door 1 of the balance case is opened, the flap 6 is allowed to close before the operator inserts his hands into the casing. If desired, the lever 10 may be swung over away from the pin 12, so that the flap 6 covers the radio-active source at all times. Where the balance case has a sliding door 17 and a hinged door 18, as shown in Fig. 3, the body 5 is pivoted on a vertical axis. The lever 10 co-operates with a bracket 21 on the door 18, and a plate 24 fixed to the body 5 co-operates with an inclined surface 22 mounted on the sliding door 17. When both doors are closed, the inclined surface 22 swings the body 5 so that the lever 10 is brought into contact with the bracket 21 to raise the flap 6. When either of the doors are opened, the flap 6 is closed again. In the arrangement shown in Fig. 7, the balance case has a vertically sliding door 17, a horizontally sliding door 26, and a small horizontally sliding door 28 which allows access to the upper part of the balance case. Door 17 has an inclined surface 22 acting as before in conjunction with plate 24 on the body 5. Similarly the lever 10 coacts with a bracket 21 on the door 26. If door 26 is opened, bracket 21 is removed from contact with lever 10 and the radiation source is shielded. A stirrupshaped member 29 is mounted on the door 26, so that if the door 28 is opened, the door 26 is also opened and the radiation source is shielded. The bracket 21 mounted on the door 26 may be pivoted, so that if desired it may be turned into a position where it does not engage the lever 10, and the radiation source is shielded at all times.