Method and appts. for locating a fault in the covering of a metal pipe buried in ground

摘要

Electric current is injected into a pipe (4) to produce a potential between the earth connection (2) and the connection (3) on the pipe. The potential difference caused by current flowing in the ground as a consequence of a fault (5) is detected by two electrodes (8) inserted into the ground. The method is characterised by the following facts: (a) the potential (C) produced is periodic and of constant sign; (b) the direction of the fault to be located is indicated by the sign of the potential difference detected. The voltage generator (11) produces a periodic potential of constant sign. The voltage measuring device (19) has a needle (19a) which can deviate in both direction from a central position. Pref. the potential (C) produced has a negative sign. There are several series of closely-space voltage pulses (12) alternating with no-voltage periods (T). These pulses are produced by relaxation oscillations of a capacitor. The voltage generator (11) pref. incorporates a capacitor. The measuring device is provided with an amplifier of variable gain, and a system allowing the needle to be automatically reset to zero.