Caltech 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.
To make it easier to interpret and to separate what is being monitored from other DC sources such as long line cells, telluric, other CP systems, etc., in the DC Voltage Gradient Technique, the asymmetrical DC signal impressed onto the pipeline is switched ON and OFF at the rate of 0.45 seconds ON, 0.8 seconds OFF. The DC signal can be impressed on top of existing CP systems or the pipeline CP Transformer Rectifiers (T/R) can be switched by using a special interrupter inserted into the negative lead from the Transformer Rectifier.