Potential Measurement under the Influence of Stray Currents

3 Potential Measurement under the Influence of Stray Currents 

Where stray currents are involved, several measurements have to be taken that are continually changing with time, simultaneously with each other. A double recorder is most suitable for this. Linear recorders with direct indication of the measurements cannot be used for potential measurements because the torque of the mechanism is too small to overcome the friction of the pen on the paper. Amplified recorders or potentiometer recorders are used to record potentials. In amplified recorders, as in amplified voltmeters, the measured signal is converted into a load-independent impressed current and transmitted to the measuring mechanism, which consists of a torque motor with a preamplifier. The amplifier results in an 

Where there are stray currents, the switching method described in Section 3.3.1 cannot be used. Stray current protection stations are usually installed where the pipeline has the most positive pipe/soil potential. When the stray current drainage is cut off, a too-positive stray current exit potential that is not 7/ -free is quickly established. In distant areas a too-negative stray current entry potential that is not 71 -free will be measured. The determination of the 71 -free pipe/soil potential is only possible in stray current areas when the origin of the stray current is not oper- 

Filters have a time constant r = R x C which increases the damping of the measuring instrument. The time constant depends on the required attenuation and the interfering frequency, but not on the internal resistance of the measuring instrument. The time constants of the shielding filter are in the same range as those of the electrochemical polarization, so that errors in the off potential are increased. Since the time constants of attenuation filters connected in tandem are added, but the attenuation factors are multiplied, it is better to have several small filters connected in series rather than one large filter. 

---