Wireless Monitoring of Power Usage by CMU

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August 27, 2013

Every electrical current creates an electromagnetic field. Remember that from physics class? Well, a team from Carnegie Mellon University is using this piece of knowledge to build a wireless meter that measures power consumption and could be used to make regular homes into an energy-efficient smart homes.

The non-intrusive load monitoring (NILM) device is just one part of an energy monitoring system being tested by CMU's Infer (Intelligent Infrastructure Research) Lab. The device does not need to be plugged into the wall or in-line with any other device, and will read EMF using just two AA batteries. It also does not have a rating that limits it from use with high-power appliances, as do other commercial power meters. It actually works better with high current devices because they create stronger EMFs.

The power consumption of a single appliance can be deduced by communicating changes in current with a central circuit panel that measures power consumption directly. By combining the EMF measurements of the NILM device with the central panel meter, energy usage can be attributed to a specific appliance.

Researchers also found they could make the system even more energy efficient with a new Time Division Multiple Access (TDMA) sensor networking protocol that's built specifically for the systems throughput data and synchronization requirements. (This most likely refers to something spawning from InferLab's Syntonistor device, a low-power, low-cost tool that provides clock synchronization to wireless devices using the induced signals from 60 Hz AC).

The system, composed of an EMF reader, the three-phase central power meter, and the communication protocol, was tested in a residential building with appliances that included an LCD TV, washing machine, toaster oven, A/C, laser printer, refrigerator, and iron. Comparing the results to those obtained with regular meters that plug in between appliances and outlets, the team found their method to work with 98 percent accuracy.

The project is being developed by Naranjini Rajagopal and colleagues at CMU's Infer Lab. The results of the research were presented at the International Conference on Cyber-Physical Systems in Philadelphia this year. The work was partially funded by Samsung, but no word yet on when a commercial system could be released.

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