GB558647A - Electric measuring, indicating, recording or controlling apparatus - Google Patents

Abstract

558,647. Impedance measurements. REDIFFUSION, Ltd., and ADORJAN, P. May 1, 1942, No. 19869/43. Divided out of 558,614. [Class 37] An apparatus for observing the impedance of a load comprises means serving to obtain a direct potential which is a function of the voltage of an alternating or pulsating E.M.F. being applied to the load, means serving to obtain a direct potential which is a function of the current being passed through the load by this E.M.F., and means automatically operative, when the relative values of these potentials depart from a predetermined relationship, to re-establish this relationship and in so doing perform an indicating, recording, or controlling operation. In the apparatus shown in Fig. 1 a transformer 4 supplies a load circuit represented by a resistance 5, inductance 6, and condenser 7, which circuit may be, for example, a public telephone line or a broadcast rediffusion network. Two pairs of terminals 8, 9 and 10, 11 are normally connected as shown in dotted lines but for measuring the impedance of the load they are connected to the measuring apparatus by terminal leads 12, 13, 14, 15. A potential transformer 16 and a current transformer 17 are connected as shown. Rectifiers 18, 19 are connected in series with the secondary windings of these transformers and a resistance 21 having a sliding contact 22 is connected between sides of similar polarity. The slider 21 is. adjusted by means of a reversible motor 20 until the potentials across the two halves of the resistance 21 are equal, the position of the slider then being dependent on the impedance of the load circuit at the frequency of the alternating E.M.F. A scale calibrated in terms of impedance may be provided. Fig. 2 shows a modification in which the change in load on the transformers 16, 17 by movement of the slider 22 is avoided. A rectifier 23 and resistor 24 are connected to the sliding contact 22 of a potentiometer resistance 25, which is connected in series with a fixed resistor 26 across the secondary of the transformer 16. Across the secondary of the transformer 17 is connected a tapped resistor 27 with a tap-selecting switch 28. This is connected to a rectifier 29 and resistor 30. A reversible motor 20 is connected between corresponding ends of the resistors 24, 30, and adjusts the slider 22 of the potentiometer resistance 25. The tapping switch 28 enables the range to be changed. The transformers 16, 17 may be tuned or filter networks may be provided so that the values of the two direct potentials are primarily dependent on E.M.F.s of a predetermined frequency. Electromagnetically operated or controlled stepping mechanism may be employed instead of a reversible motor. Differential relays may be employed to connect additional amplifying equipment in accordance with the impedance of the load on a main amplifier. Specifications 558,614, 558,645 and 558,646 are referred to.