GB717127A - Improvements in apparatus for measuring dielectric properties of materials - Google Patents

Abstract

717,127. Condensers; capacitance and moisture measurements. UNILEVER, Ltd. July 22, 1952, [July 27, 1951.] No. 17825/51. Class 37. A test capacitor for measuring dielectric properties of granular materials, plastic materials, or liquids comprises a support member of insulating. material and three or a larger odd number of coaxially displaced electrodes in the form of rings supported by coaxial with the support member. In the construction shown in Fig. the support member 1 is a hollow tube in which are embedded five electrodes 2 in the form of rings. The outside of the tube is covered by a conducting sheath 3 connected to alternate electrodes by stiff wires 4. The other electrodes are connected by a stiff wire 5 which terminates in a coaxial outlet 6. The sheath 3 is earthed and forms a screen, the outer electrodes connected to it acting as guard rings. In a modification the capacitor is in the form of a cup or beaker, the lower end being closed by an extension piece integral with the lower electrode. In another construction in the form of a dipstick a rod of insulative material has electrode rings on the outside with insulating spacer rings between them. The surfaces of the electrodes which come into contact with the material to be tested may be coated with insulating material or covered by a thin sheath of insulating material. The ring electrodes 2, Fig. 1, may alternatively be on the outside of the tube i. Fig. 5 shows a test capacitor in the form of a beaker. The support member i of insulating material is of tubular form closed at one end. Three ring electrodes 2A, 2B, 2C and two end electrodes 2<SP>1</SP> are situated on the outside of the tube. A conducting. sheath 3 is made integral with the end electrodes 2<SP>1</SP> and also covers the closed end of the tube. The sheath is connected to the centre electrode 2C by a wire 4. The spaces between the electrodes may be air-filled or filled in by an insulator 9. Separate connecting wires 10, 11 may be provided for the electrodes 2A, 2B. The support member may be of polystryene, glass, or ceramic. The electrodes may be of brass or stainless steel. The electrode rings may alternatively be formed by depositing material on the support member in the form of conductive paint such as colloidal graphite, or by metal spraying.