Plug-through energy monitor for plug load electrical devices

Abstract

We present a low-cost, plug-through energy monitor for ubiquitous electrical monitoring of plug load devices in buildings. Using a non-invasive inductive current sensing technique, the current through a plug load device is measured without a series sensing element that breaks the circuit. This enables slim profile hardware, and eliminates the series resistor power dissipation inherent in traditional current sensing implementations. Our device is fabricated using a standard PCB process with a BOM around $5, and an inductive sense coil is printed directly into the PCB. The prototype can be embedded into an outlet faceplate and easily retrofits onto any existing outlet for long-term measurement of AC power parameters. The sensor includes low-power wireless connectivity with a range of approximately 120 feet through multiple walls. Voltage and current signals are sampled at 1920 Hz for handling non-linear loads, and the measured noise floor is approximately 2.4W with 120 V RMS mains.