Thursday, 28 October 2010

Energy vs Power in NIALM

After having a play around with some real data from a Plogg connected to my machine, I began to wonder, which is more useful, energy consumption or power demand recorded from my Plogg? I plotted both over the last week:





After a glance at these two graphs, it becomes apparent that energy is not a function of power over time. In fact, a reading of the power demand at an instant in time is recorded at each interval. However, all the energy used during the interval period is accounted for from the energy readings.

These properties have both advantages and disadvantages for appliance monitoring. A major disadvantage of recording power values at time instants is that activities not taking place at the time of the reading are missed. An example of this is the spike clearly visible on the energy graph, but not recorded on the power graph.

However, the power graph does have an advantage over the energy graph. Because no averaging is done over the time interval, the reading reflects the exact sum of the appliances' power demands. This makes NIALM an almost trivial task. This is not quite so easy on the energy graph, as changes in appliance state between readings are likely and an average of both states is therefore recorded by the following reading.

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