GB532476A - Improvements in or relating to apparatus for measuring earth resistances - Google Patents

Abstract

532,476. Resistance measurements. FIDES GES. FUR DIE VERWALTUNG UND VERWERTUNG VON GEWERBLICHEN SCHUTZRECHTEN. Aug. 31, 1939, No. 25007. Convention date, Aug. 31, 1938. [Class 37] In apparatus for measuring earth resistances by passing A.C. through an earth circuit between the earthing conductor of which the resistance is to be measured and an auxiliary earthing conductor and supplying a D.C. instrument with a current corresponding to the voltage drop between the earthing conductor and a testing conductor, the A.C. is produced by a converter having oscillating contacts and supplied by a battery, the oscillating member of the converter being mechanically coupled to one or more synchronous switches for rectifying the current supplied to the instrument. One terminal of a battery 1 is connected through a switch 2 to the centre of the primary winding 3 of a transformer, the secondary winding 4 of which supplies an alternating current between the main earthing conductor 5 and an auxiliary earthing conductor 6. The other terminal of the battery 1 is connected to one end of the primary winding 3 through the exciting coil 7 of an oscillating converter and to the other end of the winding 3 through the oscillating contact 8 of the converter. In series with the secondary winding 4 is the primary winding 18 of a transformer, the secondary winding 19 of which is connected to one coil 11 of a quotient measuring instrument 12 through a synchronous switch 9. The voltage drop between the earthing conductor 5 and a test conductor 17 is applied to the primary winding 20 of a transformer the secondary winding 21 of which is connected through a synchronous switch 14 to the second coil 13 of the instrument 12. The switches 8, 9, 14 are mechanically connected. The voltage transformer 20, 21 may be omitted and the voltage drop applied to the coil 13 through two synchronous switches acting as rectifiers in current reversing connection. The current transformer 18, 19 may similarly be omitted and the coil 12 supplied through two synchronous switches. The phase of the current flowing through the earth circuit may be adjusted to correspond with the switching phase of the converter by means of reactances or capacities.