Patent GB-779913-A (GB)
Title: Apparatus for controlling gas pressure
IPC: H01J17/26
Filed: 1954-12-20
Abstract: 779,913. Automatic pressure control systems. SCHLUMBERGER WELL SURVEYING CORPORATION. Dec. 20, 1954 [Dec. 21, 1953]. No..36848/54. Class 38 (4). [Also in Groups XXVIII and XL (a)] The gas pressure in an enclosure such as an ion tube 10 is kept constant by two devices such as filaments 32, 33, each of which liberates or absorbs gas according to the temperature, which is adjusted automatically so that simultaneous evolution and absorption of gas is such as to maintain the pressure constant; pressure variations are sensed by a control system which automatically acts to eliminate them. Such pressure variations show as variations in the anode current, as indicated by the ammeter 14a, and are sensed by a servo 44 through a current transformer 41; the servo causes corresponding adjustment of one of the tappings 35, 36, with a corresponding temperature change in one of the filaments to restore the pressure. Two servos may be employed so that both filaments can be controlled independently. In an alternative control system, Fig. 4, the filaments 32, 33 are energized from a power source 34 through respective windings 62, 63 of saturable reactors 60, 61. Control windings 64, 65 are connected in series with the main discharge path 15, 18 and the coils 66, 67 of a relay 68 which actuate an armature 71; in the absence of current flow the armature is centrally maintained by springs 72, 73. A series of movable contacts 85 ... 89 engage either the series of fixed contacts 80 ... 84 or the series 75 ... 79, according to the position of the relay armature 71. The reactors also include windings 69, 70, which are joined through movable contacts 88, 89 and the fixed contacts on either one side or the other to a potentiometer 98 across a source 92; the connections are arranged so that as the relay contacts move across from one side to the other, the current through windings 69 and 70 is reversed. A variable resistor 99 is connected from the junction of coils 69, 70 through the relay contacts to either of the other ends of coils 69, 70. When the armature 71 engages the core of coil 66 (first operating position), the magnetic fields of coils 64 and 69 are in opposing relationship, so that the impedance of coil 62 varies directly with the current in coils 64, 65; the fields of coils 65 and 70 are in aiding relationship, so that the impedance of coil 63 varies inversely with the current in coils 64, 65. When the relay contacts move across to the other side (second operating position), the converse holds. Initially, the armature 71 is manually displaced to the first operating position. Potentiometer 98 and variable resistor 99 are so adjusted that the respective currents through filaments 32 and 33 give the desired rates, of gas absorption and emission. An increase of pressure in the tube 10 causes an increased current in the tube and through the coils 64 and 65, with a corresponding increase in the impedance of coil 62, and vice versa for coil 63. Thus, filament 32 becomes cooler and emits less gas, while filament 33 becomes hotter and emits more; consequently the pressure is restored. The converse occurs if the gas pressure decreases. Eventually, the emitting filament becomes exhausted of gas, while the absorbing filament becomes saturated. Their functions may then be reversed, and provision is made for this to occur automatically. As the pressure falls, the current through coil 66 becomes insufficient to retain the armature 71 which, under the action of spring 73, is carried across to coil 67. This reverses all the relay contacts, and the second operating position is obtained, reversing the current through coils 69 and 70, and shunting resistor 99 from one coil to the other. In order to hold the armature in one or operating position until the current in the tube builds up sufficiently to retain it, condensers 90, 91 are connected through respective pairs of contacts 86, 81 and 85, 75 across the power source 92. As one or other operating position is made, one of the condensers discharges through the corresponding coil 66 or 67 to hold the armature for a short interval. As shown, in either operating position, one of the condensers discharges, while the other is recharging ready for the next reversal.