signal-to-noise ratio (SNR) of the 20 sediment traps. The first test involved

measuring the tare-weight of the traps, as the empty traps hung freely in the air

and the facility was drained. Data were collected on all 60 load cells

simultaneously for a duration of 80 sec, at a sampling rate of 1 Hz, which would

be the typical sampling frequency used during experiments. The average,

standard deviation, maximum, and minimum values of the instantaneous weights

in each time series were calculated. The total tare-weight of all 20 traps was

calculated to be 2,888 kg. This is essentially the total weight of the materials

(aluminum and stainless steel) used to fabricate the traps.

Figure 24 shows the minimum and maximum value divided by the average

value for each of the 60 time series. The greatest ratio of either the minimum or

maximum value divided by the average value was approximately four percent,

and only one percent on average (for all 60 load cells). The third time series is

plotted as one plus the ratio of the standard deviation divided by the average

value. This ratio was at most 0.6 percent and about 0.3 percent on average.

1.05

Maximum/Average

1.04

Minimum/Average

1.03

1+(Std. Dev./Average)

1.02

1.01

1.00

0.99

0.98

0.97

0.96

0.95

0

5

10

15

20 25 30 35 40

45

50

55

60

Figure 24. Statistical parameters normalized by the average value in the time

series, obtained from each load cell during tare-weight tests

conducted with the traps empty and the facility drained

Figure 25 shows the standard deviation of each time series. These are the

same data as the third time series of Figure 24 but plotted in terms of absolute

weight, rather than normalized by the average value. As shown, the standard

deviation was always less than 0.35 kg for average load cell readings ranging

from 22 to 97 kg. On average, the standard deviation was about 0.15 kg. This

magnitude of the SNR for the 60 load cells is considered excellent.

42

Chapter 4

Sediment Trapping and Dredging Systems

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