The Model PD Detector and null Method have been well accepted by the industry. Acclaimed to be the fastest method known to accurately locate points of electrical contact and insulating joints on coated pipelines. This type survey may be conducted on coated pipelines regardless of their location. Unaffected by parallel lines, depths or cover, the survey can often be, in part, conducted from a moving vehicle over the pipe. In brief, the Null Method follows the flow of impressed audio frequency current in a coated pipe and determines where it leaves. The point of current discharge is determined by a sharp disturbance of the null itself rather than the signal level of the audio frequency. This method is quite practical, particularly as competent field personnel can interpret findings quickly and accurately.