points may have different temperatures the potential difference between the point 302 and the point 304 is the potential difference of interest and may be measured via a connection 306 the reference points 308 and 310 reside within the bulk fluid 312 and are not affected by temperature deviations connection 314 allows the potential difference between the contact point 302 and the bulk fluid reference point 308 to be measured connection 316 allows the potential difference between the contact point 304 and bulk fluid reference point 310 to be measured because of potential temperature differences at the pipe wall thermocouple effects induce some of the voltage measured at the contacts by measuring the voltage differences between the contacts and the references these effects can be compensated for and the true potential difference between points 302 and 304 can be calculated the accuracy of the pig 39 s data may also be adversely affected by no contact events no contact events refer to an event in which the electrical contact between the pig and pipeline is interrupted those skilled in the art will recognize that no contact events result in undesirable open circuit signals to detect no contact events the present invention may include an alternating current ac pilot signal to flag and exclude no contact signals during data processing for example if a 1 u2013 10 khz ac voltage source of.