Patent GB-486112-A (GB)
Title: Improvements in electrical measurement apparatus
IPC: G01R1/30
Filed: 1936-10-28
Abstract: 486,112. Correspondence - control systems. ELECTRIQUE, ASSOCIATION CO-OPERATIVE D'OUVRIERS EN MATERIEL ELECTRIQUE. Oct. 28, 1936, Nos. 29359 and 29360. Convention dates, Oct. 29, 1935 and July 28, 1936. [Class 40 (i)] [Also in Groups XXXVI and XL] An electrical measurement apparatus comprises a number of test bodies 1, 1<1>, included in one arm respectively of each of two Wheatstone's bridge networks and adapted to be exposed to the phenomena the variations of which are to be measured so that as a result of these variations the out-of-balance currents flowing in a diagonal of each bridge is varied, the bridges being such that as the out-of-balance current in one bridge increases that in the other decreases and vice versa, and a measuring device being connected to the bridge diagonals to indicate the resultant effect of the out-ofbalance currents. The out-of-balance current in one bridge may be a maximum while that in the other is a minimum or the two currents may start at a common value and one increase while the other decreases. The test bodies may be resistances of platinum or carbon the values of which vary with temperature, or thermo-couples may be used, when temperatures are to be measured; and in psychrometric measurements, using wet and dry bulb thermometers, the test bodies are subjected to the temperatures of the wet and dry bulbs respectively. For measuring ionic conductability, the test bodies may be pairs of electrodes inserted in the liquid under test and for measuring the level of liquids, variable resistances immersed therein or controlled by floats may be used. Finally, the test bodies may be formed by condensers the dielectric of which is the fluid to be tested. The measuring instrument may be a cross-coil or a differential type of instrument. In a specific example, the device forms a pyrometer having a blackened platinum wire 16 which is divided into two parts to form the test bodies 1, 1<1>, each of which is connected in the two resistance-bridge systems shown and the outof-balance currents of which are measured by the instrument C. The wire 16 which may be mounted in a gas-filled or evacuated envelope 17 is situated on the focal line of a cylindrical or other lens 13 which focuses the heat rays on to the wire 16. When used for spectropyrometry a slotted screen and a rotatable prism, provided with adjustment screws and scale, are arranged between the source of heat and the lens 13 so that rays of any selected wave-length may be caused to fall on the wire 16. The two bodies 1, 1<1> may not be identical and may be of different substances. The lines connecting the test bodies to the bridge resistances or the latter and the measuring instrument may be of any desired length and when the device constitutes a thermometer the bridge resistances may be mounted on the thermometric rod comprising the test device. The Specification as open to inspection under Sect. 91 comprises also the application of the device to the measurement of current and voltage and describes an ammeter in which the test bodies are constituted by thermo-couples t, t<1>, Fig. 8 (Cancelled), connected as shown to the current-carrying line l and each forming one arm of a bridge network. The flow of current heats the junctions s, s<1> and this produces an e.m.f. in each thermo-couple which affects the out-of-balance current in each bridge. In another arrangement there are provided two adjustable resistances, each forming an arm of the bridge, and both are adjusted by means of tapping arms controlled by a common shaft. Finally, it is suggested that only one of the test bodies need be variable under the action of the phenomena to be observed. This subjectmatter does not appear in the Specification as accepted.