Patent GB-819726-A (GB)
Title: Apparatus suitable for use, or as part of, high frequency power volt meters
IPC: G01R1/067
Filed: 1955-11-16
Abstract: 819,726. Voltage, power measurement. BIRD ELECTRONIC CORPORATION. Nov. 16, 1955 [Nov. 16, 1954], No. 32860/55. Class 37. [Also in Group XL (b)] Apparatus for measurement of high-frequency voltage or power comprises a coaxial line of which at least a part of the length of the inner conductor constitutes a resistor, a pick-up assembly mounted on the outer conductor and carrying a probe which projects through an aperture in the outer conductor at a point of the latter intermediate its ends; such probe extending across the annular dielectric space between the inner and outer conductors to make electrical contact with the resistor of the inner conductor at a point between its ends and being connected through a rectifying circuit to a D.C. galvanometer. Figs. 1, 2 show a threaded coaxial coupling element connecting a line (not shown) to a termination section comprising an inner resistive rod 2 (which may be a film resistance) coupled at one end to the inner line conductor over socket 17 and at the other end over recessed threaded plug 4 to an outer conducting sleeve 1, which is internally tapered at 3 to a horn profile so as to present a characteristic termination impedance to the input line. A conductive hollow shell 24 slidable externally over sleeve 1 and clamped thereto by a pinch bolt 70 is internally chambered to receive a rectifier unit 29 containing a germanium pellet 35 contacted by wire 36, which is positioned by insulating rings 51, 52, 53 and an insulating cap 54 depressed by a spring 58 bearing against threaded outer closure cap 55. The lower pole of the rectifier unit carries a probe 31 which is pressed by the spring into slidable contact with resistive rod 2 and the upper pole is contacted by resilient fingers 64 of ring 61 insulatedly surrounding the rectifier unit. A socket in the ring receives spring plug connector 66 connected to the centre contact of button capacitance 41 and to resistance 46 connecting to the centre of button capacitance 42 and to terminal 45 insulatedly mounted on plug 44, retained by a flange 47 of a cylindrical conductive shell 40 screwed into shell 24 at right angles thereto; the plug also retaining the button capacitors separated by conductive sleeve 43 and connecting their remaining poles to the outer sleeve 1. A galvanometer G is connectible between terminal 45 and shell 40 to measure after rectification a voltage proportional to that developed along resistive rod 2 for the position of its length between plug 4 and slidable probe 31, which thus constitutes with the resistance a voltage divider potentiometer for modifying the measurement sensitivity. The resistive rod 2 may have metal sprayed contacts band at its ends, and spaced bands disposed along its length to improve the contacts with socket 17, plug 4, and slider 31. Alternatively, the galvanometer may be used to indicate power dissipated in the portion of the resistive rod between the slider and the plug and the value of resistance 46 is suitably chosen for correct calibration. In a modification (Figs. 6, 7, not shown), the rectifier with its associated resistance and capacitances are mounted in a casing integral with the outer sleeve of the coaxial termination fitted with a plug for the galvanometer connection, while the probe is a flat beryllium copper spring contacting the resistive rod and mounted by two screws on an insulating block; one screw passing through a circular hole in the spring and the second traversing an arcuate slot allowing rocking movement of the spring for adjustment over the resistive rod. Specification 702,357 is referred to.