GB822574A - Electric transducer - Google Patents

Abstract

822,574. Electric indicating systems. LION, K. S. Nov. 6, 1956 [Dec. 7, 1955], No. 33860/56. Class 40 (1). [Also in Group XL (a)] Sputtering of the internal principal electrodes in the discharge tubes of transducer systems as described in Specification 762,914, is avoided by positioning the auxiliary electrodes so as not to overlap the principal electrodes so that the principal electrodes are not immersed in the plasma of the discharge. In one arrangement, Fig. 1, the gas-filled glass tube 1 contains two internal principal electrodes 3 and 5 connected to output terminals 2 and 4. External auxiliary electrodes 6 and 7, spaced from the tube 1 by small air spaces 8 and 9, are connected to a source 10 of alternating current, preferably of radio frequency, which maintains in the tube 1 an ionized region (shown shaded in the Figure). The ionized region remains substantially localized to the left of the dotted line A-A. Relative movement between the tube 1 and the electrodes 6 and 7 produces a D.C. output at the terminals 2 and 4. In a modified arrangement, Fig. 2, the electrodes 6 and 7 are disposed on the tube envelope and a capacitor 11 or other variable impedance element is connected between electrodes 3 and 6 to vary the A.C. potential on electrode 6 relative to that on electrode 7. The variable capacitor 11 may be controlled by any desired physical change (e.g. a change in humidity) or movement to produce an output signal at terminals 2 and 4. A further variable capacitor may be connected between electrodes 4 and 6. The electrodes 6 and 7 are preferably shaped as part-cylinders, each surrounding about one-third of the periphery of the tube 1, but may alternatively be single wires or may be in the form of conductive paint painted or sprayed on the tube wall. In further modified arrangements the electrodes 6 and 7 are in the form of plates positioned inside the tube so that the electric field between them is at right angles to the plane formed by electrodes 3 and 5, and each electrode 6 and 7 is connected through a variable capacitor to each of the electrodes 3 and 5, or alternatively electrode 6 is connected to the movable plate of a differential capacitor connected between electrodes 3 and 5. In some applications one or more of the variable capacitors may be omitted or may be replaced by the stray capacitance between electrodes.