Non-Contact Power Metering

According to Maxwell’s equations, any electric current generates a magnetic field, and any difference in voltage generates an electric field. Therefore it is (at least theoretically) possible to measure the voltage and current in a wire from a distance, without making direct electrical contact with the wire. This principle is familiar to anyone who has ever used a clamp-on current meter.

What if multiple wires, with different voltages and currents, are in close proximity? The electric and magnetic fields generated by each wire will superpose linearly. In theory, it should still be possible to determine all of the voltages and currents by monitoring the nearby electric and magnetic fields. In practice, this becomes quite complicated.

I developed a mathematical framework for describing the non-contact sensing problem, and algorithms for scaling up non-contact sensing to large numbers of independent sources with large numbers of sensors. A brief summary of these results is given in:

David Lawrence, John Donnal, et al., “Current and Voltage Reconstruction from Non-Contact Field Measurements”, IEEE Sensors Journal (August, 2016).

Non-contact voltage sensing presents a particular challenge in that electric field sensors are highly susceptible to switching noise from electric loads in the vicinity. I developed a new electric field sensor and signal processing algorithms to improve the disturbance rejection characteristics of non-contact voltage measurements.

David Lawrence, John Donnal, et al., “Non-Contact Measurement of Line Voltage”, IEEE Sensors Journal (December, 2016).

These projects occurred under the larger umbrella of my master’s thesis, titled “Hardware and Software Architecture for Non-Contact, Non-Intrusive Load Monitoring”. The Wattsworth project, maintained by John Donnal, represents an ongoing effort to make practical use of this non-contact sensing technology.

State-of-the-art non-contact voltage measurement.

State-of-the-art non-contact voltage measurement.