GB1311297A - Precision variable-resistance high resistance devices for high frequency use - Google Patents

Abstract

1311297 Measuring dielectric constant TODAI MUSEN K K 11 Aug 1970 [15 Aug 1969 16 June 1970] 38668/70 Heading G1U [Also in Division H1] A capacitor and resistor assembly providing a standard variable high resistance suitable for use in measuring dielectric constant and loss angle of an insulator at high frequencies comprises two parallel plate capacitors of capacitance C 1 and C 2 the adjacent plates of the capacitors being constituted by metal layers on opposite surfaces of plate 2 of dielectric material, or alternatively by a single metal plate, Figs. 5A and 6A (not shown), plate 2 or the single plate being displaceable at right angles to the parallel electrode plates by measurable small distances, and a resistor R 5 , Figs.1B and 1C (not shown) and Fig. 4, being connected in parallel with capacitance C 2 . Preferably R 5 and C 2 are chosen so that (2#f)<SP>2</SP> C 2 <SP>2</SP> R 5 <SP>2</SP> ” 1 wherein f is frequency. As shown, the other plate of capacitance C 1 is common to a fixed capacitor comprising metal layers on plate 1 of dielectric material of dielectric constant # s , as is the material of dielectric plate 2. The other electrode of capacitance C 2 is a metal layer on dielectric disc E and is earthed. It is shown that for small displacements #t of plate 2, the capacitance between terminals T 1 and T 2 does not vary but the resistance Rpx between the terminals varies with the displacement according to the relationship:- wherein # 1 is the dielectric constant of the fluid dielectric of capacitors C 1 and C 2 , t s =t s1 +t s2 , the thicknesses of plates 1 and 2 respectively and t 1 and t 2 are the electrode spacings before displacement of capacitors C 1 and C 2 respectively. To measure the resistance R x of a test substance of capacitance C x , Fig.4, the circuit is tuned with switch S open using capacitor C v , then tuned again with switch S closed. Plate 2 is now displaced until the current flowing in the detector circuit rises to the value it had at the first tuning. Then R x is given by:- which may be simplified by making t 1 = t 2 and having air as the fluid dielectric. Minor variations of the capacitor-resistor assembly, Figs. 5A and 6A (not shown), and measuring circuit, Figs. 5B and 6B (not shown), are disclosed.