Electric circuits for the measurement of electrical quantities (with particular reference to the measurement of arc loss in mercury-arc rectifiers)

Established methods of measuring are loss in mercury-are rectifier's are surveyed and examined critically. In particular the difficulty of obtaining a satisfactory instrument deflection is discussed. Two new methods developed by the writer, incorporating a dynamometer instrument are then described. The first of these requires protective gear of lighter rating than is required by the established methods, but provides a smaller instrument deflection. The second also requires protective gear of only light rating, but provides about twice the Instrument deflection obtainable with the established methods. In the second half of the thesis, a survey of established methods of electronic multiplication by analogue circuits is given, followed by a description of a logarithmic multiplier developed by the writer, which incorporates a moving-coil instrument and which is suitable for power measurement, particularly with interrupted d.c. waveforms of the type encountered in the anode circuit of a mercury-are rectifier. The circuit performance of the various units of the multiplier is examined in relation to the degree of accuracy required. Test figures demonstrating the performance of the multiplier with various types of input are given; and a brief description of a proposed extension of the system to deal with alternating quantities is also included. The a.c. mains stabilizer circuit used to regulate the power supply to the electronic circuits of the multiplier is described in outline.