Caltech Engineering Services- India offers basic and standard DCVG equipment.
DCVG-UK manufactured useful equipment. when DC is applied to a pipeline in the same manner as in cathodic protection, a voltage gradient is established in the ground due to the passage of current through the resistive soil to the bare steel exposed at a coating fault.

The voltage gradient becomes larger and more concentrated the greater the current flowing and the closer you are to a coating fault location. In general,  the larger the fault, the greater the current flow and hence bigger the voltage gradient.

The direct current voltage gradient method (DCVG) uses a sensitive mili-volt meter, to indicate the potential difference between two copper/copper sulphate half cells placed in the soil in the voltage gradient at ground level. If spaced two metres apart in a voltage gradient, one half cell will adopt a more positive potential than the other, which thus enables the size of the gradient and direction of the current flow causing the voltage gradient to be established.