WRT-10 - Winding Resistance Tester
The WRT-10 injects a DC current through the windings & measures the voltage drop. The instrument calculates the resistance R= E / I. The challenge in winding resistance measurements is that the voltage across an inductor is defined by V = L (di/dt), where L is the inductance of the winding & (di/dt) is rate of change of current. Therefore small changes in the current, as may be caused by ripple or poor regulation, can make it impossible to measure the DC resistance. The highly regulated and filtered current output of the WRT-10 allows for winding resistance measurements on very large power transformers.