GB294792A - Improvements in instruments for the measurement of alternating potential differences - Google Patents

Abstract

294,792. Moullin, E. B. Sept. 17, 1927. Pressure meters.-An instrument for measuring alternating voltage comprises a three-electrode valve having asymmetric conductivity between the anode N and filament L and also between the grid M and the filament, the alternating voltage to be measured being applied between the grid M and filament L and the increase of the anode current being measured by means of a galvanometer G connected between the anode N and a point A slightly positive with respect to the positive side of the filament and calibrated directly in terms of the applied alternating voltage. No separate anode battery is employed. The circuit of the filament battery includes a resistance AB of such a value as to make the positive terminal of the filament L about 0.8 volts negative to the positive terminal of the battery. In the same circuit is a fixed resistance CD of such a value as to make the point D about 1 volt negative to the negative terminal of the filament, and an adjustable resistance DE to permit adjustment of the filament current to its standard value. The galvanometer G is provided with alternative shunt resistances 0, P, Q for varying the range and is also shunted by a condenser C<1> of about 1 microfarad capacity. A calibrating switch S enables the filament and grid to be connected. The grid M is connected to the point D through a resistance R of about 1 megohm and to one terminal H of the alternating voltage through a condenser C<2> of about, one microfarad capacity. The other terminal F of the alternating voltage is connected to the point D. Alternatively the resistance R may be connected in place of the condenser C<2>, which is omitted.