AMPP Cathodic Protection Technician (CP2) Practice Exam

To determine the residual magnitude, it's important to first understand what is meant by "residual magnitude" in the context of cathodic protection testing. Residual magnitude typically refers to the effect of the test current on the voltage readings before and after the current is applied. Here, the voltage readings have changed from +21mV before the test to -19mV after the test, indicating a shift due to the applied current. To calculate the residual voltage change, you would subtract the final voltage reading from the initial voltage reading: Initial voltage: +21mV Final voltage: -19mV The change in voltage is: Residual Voltage = Final Voltage - Initial Voltage Residual Voltage = -19mV - (+21mV) Residual Voltage = -19mV - 21mV Residual Voltage = -40mV Next, apply the calibration factor to convert this voltage change into a residual magnitude (current). The calibration factor is given as 0.25 A/mV. Therefore, the residual current can be calculated as follows: Residual Current = Calibration Factor × Residual Voltage Residual Current = 0.25 A/mV × -40mV Residual Current = -10A The