GB491772A - Improvements in or relating to the measurement of electric power, particularly high-frequency electric power - Google Patents

Abstract

491,772. Power meters. SIEMENS & HALSKE AKT.-GES. March 2, 1938, No. 6619. Convention date, March 3,1937. [Class 37] A bridge arrangement for measuring power, particularly at high frequencies, has one diagonal supplied with a current proportional to the voltage, the other diagonal containing the secondary winding of a current transformer for the current to be measured, and two adjacent bridge branches each containing a rectifier having a square-law characteristic in the working range so as to supply a direct current corresponding to the square of the current flowing through the associated bridge branch, the other two bridge branches preferably containing resistances of relatively high ohmic value. A current transformer 3 has its primary winding in series with an A.C. source 1 and a load 2, the secondary winding being in one diagonal of a bridge, the other diagonal of which is supplied by the voltage U. As shown in Fig. 1, two arms of the bridge are formed by high resistances 5, 5<1>, the other two branches comprising resistances 8, 81 connected in the grid circuits of valves 9, 9<1>. Condensers 11, 11<1> prevent alternating currents from passing through a common anode battery 12 through resistances 13, 13<1> to the anodes of the valves 9, 9<1>, the anodes being connected by a moving coil instrument 14. The grid biassing potential of the valves is so determined by a common battery 10 that they work on the quadratic portions of their characteristics. The instrument 14 is traversed by a direct current which is proportional to the difference of the anode currents of the valves 9, 9<1>, corresponding to the squares of the sum and difference of the current and voltage of the circuit. In a modification, Fig. 2, a double diode 15 has its anodes 19, 19<1> connected to the junctions between the resistances 8, 8<1> and condensers 16, 16<1>, the cathode 18 being connected to the junction between the coils 17, 17<1> of a double-coil instrument and also to the diagonal point of the bridge supplied with the voltage U. The double diode may be replaced by dry rectifiers in parallel with the resistances 8, 8<1>, in which case the indicator may be a single moving coil instrument connected, in series with choking coils, between the junctions of the resistances 8, 8<1> and condensers 16, 161.