Methods and devices for establishing the relationships between the conductor currents and sensor outputs for cases where the geometric parameters of the conductors and sensors are unknown. The methodology involves a sensor calibrator. This device is connected to the conductors at a location downstream of a number of current measuring devices or current sensors. The calibrator draws specific currents from the conductors for a short period in an automated manner. The characteristics of the currents drawn by the calibrator such as the magnitude and frequency of the currents are known to the processing unit for the sensors through means such as communications. The processing unit uses these known currents to establish the relationship between the conductor currents and its sensed quantities. This process may take a few seconds. Once the relationship is established, the sensors can start to “measure” the conductor currents by calculating them using that relationship and its sensed quantities.