Patent GB-516602-A (GB)
Title: Improvements in or relating to high-frequency measuring resistances and methods of measuring employing such resistances
IPC: G01R17/10
Filed: 1938-06-30
Abstract: 516,602. Temperature-variable resistances; combinations of resistances; non-metal resistances; resistance measurements. SIEMENS & HALSKE AKT.-GES. June 30, 1938, No. 19466. Convention date, July 15, 1937. [Class 37] [Also in Group XXXVIII] A measuring resistance for high-frequency measuring apparatus consists of a material having a positive or negative temperature coefficient such that the value of the resistance varies continuously with temperature over a wide range, means electrically separate from the high frequency measuring apparatus being provided for varying the temperature of the resistance in order to adjust its value during the high-frequency measurement. Suitable materials for resistances having a negative temperature coefficient are carbon or pressed or calcined metal oxides, such as uranium dioxide. Iron-hydrogen resistances may be employed when a positive temperature coefficient is desired. In the arrangement shown in Fig. 2, two equal resistances 2R are connected in parallel in the high-frequency circuit HF whilst they are in series in the heating circuit Hz, a condenser C being provided for decoupling the high-frequency circuit HF from the heating circuit Hz. In an alternative arrangement, Fig. 3, four resistances R are connected in bridge formation. A symmetrical arrangement is shown in Fig. 4, in which two resistances 2R are in parallel and each is earthed through a condenser 2C. As shown in Fig. 5 the high-frequency measuring resistance HFR is connected in a low-frequency auxiliary measuring bridge and the desired resistance value is produced by adjusting a standard resistance N to this value and regulating the heating current by means of a resistance Rh until the bridge is balanced, or the heating may be first regulated and the standard resistance then adjusted to balance the bridge. The heating potential also serves as measuring potential for the auxiliary bridge. In a modification, Fig. 6, the heating energy is obtained from the output of an amplifier. The highfrequency measuring resistance HFR is connected in the auxiliary bridge, of which the bridge diagonal 1, 2 is connected to the input of an amplifier consisting of valves VR1, VR2, AD1, AD2 and associated transformers U1, U2, U3. The transformer U1 is connected to the output of the amplifier and supplies the heating current for the measuring bridge, derived from the supply mains and from the anodes of the valves AD1, AD2. The heating current is consequently adjusted in accordance with variations in the potential across the diagonal points 1, 2 of the auxiliary bridge. The highfrequency resistances may be tubular to reduce their thermal inertia. The resistance material may be in the form of a plug of circular crosssection having a central pin forming one terminal and an outer earthed conductive coating or cover forming the other terminal in order to reduce its capacity and minimize the lengths of the connecting leads. In alternative arrangements the resistance may be thermostatically controlled or its temperature may be varied in accordance with a controlling value such as pressure, tension, or vacuum. The high-frequency resistance may also be employed in remote control or measurement, the standard resistance being arranged at the point of transmission and the heating energy being transmitted through a long distance line.