CATHODIC PROTECTION | Understanding Potential Measurements

Cathodic Protection engineer, Neil Webb, brings his experience and expertise on the importance of understanding potential measurements on your CP system. From negatives to unit conversions, Neil discusses the tips and tricks for accurately measuring and interpreting the potential of your system.
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[@dentalmanuk]

Excellent discussion .. despite having CP experience we learn .. we didn't talk about 100mV shift potential Citroen

[@rogeralexander4038]

We cannot measure a potential, but we measure potential differences in units known as volts. Gibbs Free Energy explains that there cannot be zero potential as the free energy fills any void. Therefore there cannot be a negative potential so we must examine the measurement itself. If we are using an old analogue voltmeter there must be current flowing through a coil that moves a magnet on a pivot against the elastic memory of a hair spring. the pointeris fixed to the magnet and adjutment can be made to the anchor point of the hair spring to zero the meter before a measurement is made. We set the instrument zero and measure the potential difference in relation to that zero. If we are using a digital multimeter it does noh have a hair spring but is entirely electronic. It consists of a series of capacitors and resistors that can be likened to cups and byepasses. The charges pass into the cup and when it is full pass on to the next cup. The value of each resistor is known and the eletrical capacity of energy (potential) is known. The wiring is designed so that the display shows the voltage or current flowing through the resistors to complete the measuring circuit. An oscilloscope displays the path of an electron across a screen that has to zero adjusted for each reading or series of readings. It is therefore the meter that sets the zeron for each 'pipe-to-soil VOLTAGE measurement. The ground contact electrode is not a reference potential. All of this is described in detail in Module01 of the CPN on-line Corresspondence Course at the following link. www.pipeline-corrosion-control.net/CorrespondenceCourse/Module01/index.html