GB555134A - Improvements in or relating to apparatus for measuring low gas pressure - Google Patents

Abstract

555,134. Measuring pressure. KLEMPERER, O. E. H. Feb. 3, 1942, No. 1406. [Class 37] [Also in Groups XIX and XL] A pressure gauge comprises an electric discharge device adapted to be immersed in the atmosphere of which the pressure is to be measured, said device including a cathode substantially surrounded an anode and means for causing electrons to travel in long paths between cathode and anode so that sufficient ionization takes place to produce a desired indicating current. The cathode C is a cylinder having end discs through central holes in which a rod A of tungsten wire passes, the wire having been dipped in thorium nitrate and warmed up gently to provide a thin radio-active coating of thorium oxide on the anode. The electrodes are set up in a bulb T communicating by a pipe V with the space in which is the gas to be measured. A solenoid M disposed coaxially with the cathode C provides the axial magnetic field. The cathode is earthed through a microammeter ÁA, while a voltmeter KV is provided for measuring the voltage between the anode and cathode. In a preferable indicating circuit, Fig. 5, the load resistance is in the cathode lead and comprises a high resistance N and a lower resistance R, the voltage across the latter being amplified in a variable valve V1. In a modification, the valve is connected to operate as a cathode follower valve and a voltameter across the device AC is adjusted until the milliammeter gives the particular indication corresponding to a particular current through the device AC. In a final form, the instrument MA is dispensed with and a visual indicator used of the kind described in Specification 481,790 and known as the " Magic Eye " the pattern on which closes at a particular value of the current through the gauge and the vacuum is determined by the voltage across AC when the pattern just closes. The voltage is derived from a potentiometer in connection with a main supply. Specifications 474,845, 481,790, [Group XL], and 493,274 are referred to.