
A connection of separate measurement cable to the cathode connection point may be needed for the reference electrode. This is due to the erroneous voltage of measurements done over the current carrying cathode cable. Moreover, if the cathode cable breaks, measurements cannot be taken from the reference electrode and the cathode cable breakage cannot be detected by the system. If the cathode cable is too short or the working current is too low this error amount may be too low that it can be omitted.
The error amount caused from cathode cable can be calculated as follows;
Erroneous measurement is caused by the voltage drop over the cathode cable,
This voltage will be:
V(cathode) = I(cathode) * R(cathode)
I(cathode) current can be read out from the display while the system is operating.
Cathode cable resistance can be calculated by the formula
R(cathode) = Cable length / (56 * Cable cross section)
Example;
I(cathode) = 10 A
Cathode cable length = 50 m
Cathode cable cross section = 25 mm²
R(cathode) = 50m / (56 *25 mm²) = 0,0357 Ohm and
V(cathode) = 10 A * 0,0357 Ohm = 0,357 V
This erroneous measurement voltage is added to the value read out from display.
In this case a separate measurement cabling for reference electrode is inevitable.
If we consider system current to be 0.1 A, erroneous voltage will be;
V(cathode) = 0,1 A * 0,0357 ohm = 0,00357 V (3,57 mV)
This value is too low. In this case there may be no need for second measurement cabling in terms of erroneous measurement.
It is strongly recommended that a separate cathode cable for measurement purpose to be installed in new systems. This measurement cable’s cross-sectional area has not great importance but it is foreseen that according to its place of use or length of the line, cables with 6mm² or thicker cross-sectional area are to be proper for mechanical robustness.