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Wireless Sensor and Actuator Networks for Lighting Energy ...

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luminaires were used to simulate extraneous lighting. The setpoint of this experiment<br />

was specified at 550 lux at all times.<br />

Figure 7-12(a) shows the fused values (blue solid line) <strong>and</strong> the readings from<br />

one of the mote sensors (magenta dashed line) gathered at the computer. For clarity <strong>and</strong><br />

readability, the raw data from the other five sensors are omitted in this plot. The big<br />

spikes indicate the times when the overhead lights were turned on or off <strong>and</strong> the overall<br />

illuminance on the desktop was rapidly brought back to 550 lux. Due to the large<br />

number of data points squeezed into the plot, the fused line in Figure 7-12(a) seems<br />

thick <strong>and</strong> fluctuates significantly. Figure 7-12(b) focuses on the fused value from the<br />

first half hour of Figure 7-12(a) to show the per<strong>for</strong>mance of the system with better<br />

resolution. The desktop illuminance was regulated within 5% of the setpoint during the<br />

entire experiment. The magenta dashed line, which is based on the raw readings from<br />

sensor No.3, stopped around the fourth hour because the mote ran out of batteries. The<br />

fact that the blue line, the fused values, was not affected by the malfunctioning sensor<br />

verified the robustness of the mote-FVF algorithm under sensor failure.<br />

(a)<br />

(b)<br />

Figure 7-12 Long term desktop illuminance regulation.<br />

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