| 摘要 |
896,546. Indicating liquid levels. BENDIX CORPORATION. July 25, 1960 [Aug. 3, 1959], No. 25872/60. Class 123(1). A high and low level alarm apparatus especially for liquids such as liquid oxygen, which utilizes the difference in heat conductivity of the liquid and its vapour, consists of an expansible capsule 20 from which depends into a dewar flask 10 containing the liquid a small bore tube 18 housed within an evacuated insulating tube 25. Immediately below and above the preset high and low levels the tube 18 emerges from the tube 25 and is wound therearound in single turn coils 26, 27. The capsule and tube 18'are partly filled under a pressure slightly exceeding that in the flask with a liquid, preferably that contained in the flask. Heating coils 28, 29 are provided adjacent the coils 26, 27 respectively and are supplied with current from a source 42 through a manual switch 38 and respective resistances 51, 50, the latter being shunted by switches 41, 40 which are actuated together with alarm circuit switches 44, 45 by the movements of the capsule via a rod 46. In operation, assuming that the flask contains liquid oxygen 11 to a level. Z, on closing the switch 38 a low current flows through the heaters 28, 29 slightly warming the tube 18. Heat dissipation from the coil 26 in the gas space 12 is insufficient to produce condensation therein. Condensation occurs in the coil 27, however, since this coil is immersed and the capsule 20 partly collapses to the condition shown, switches 40, 45 being closed whilst switches 41, 44 remain open. When the switch 40 closes the resistance 50 is shorted and the heating of the coil 27 thereby increased. The increased heating is insufficient to cause evaporation within the coil but serves, if the liquid level falls below the coil, i.e. to the preset "low'' level, to cause a quick evaporation of its contents and a rapid response of the apparatus to the low level condition, the capsule expanding fully to cause switches 40, 45 to open, the switch 45 being so connected in a low level alarm circuit W, W that the alarm is given. When the liquid reaches the high level Y it covers the coil 26 and condensation of the fluid therein occurs. The capsule contracts fully, thereby closing switches 41, 44. The switch 41 shorts the resistance 51 to increase the heating of the coil as described for the coil 27, whilst the closing of the switch 44 ,energizes a high level alarm in the circuit X, X. |
