Campbell Scientific OBS-Mobile Software for Archer-OBS - Manual (Page 15)

Section 1. Operations
interval that will show the changes in turbidity and water depth that you wish
to investigate. Rate sets the number measurements per second, in Hz, taken
during a sample. The quicker turbidity and depth change, the higher the
sampling rate should be to get a stable average value for a sample. Finally,
Duration sets the period of time for measurements and how long sensor
outputs will be averaged. For example, with an interval of 30 seconds and a
duration of five seconds, the OBS-3A will make measurements for five
seconds starting every 30 seconds. The number of measurements in a sample
(sample size) is the product of the duration and the rate. So if the rate was 25
Hz in the prior example, the sample size would be 5 X 25 = 125 measurements.
TABLE 1-1 provides some recommended ranges for these parameters in
various sampling environments. Always select duration and rate to give a
sample size of at least 30, and to reduce random sampling noise below 50% of
its maximum value, select them to give a size greater than 200.
TABLE 1-1. Sampling Schedules
Environment Rate (Hz) Duration (sec) Interval
River/Stream 2-5 30-100 300-900
Beach 5-25 30-200 60-900
Estuary 5-10 10-60 600-3600
1.10 Sampling Modes
Survey: Select the survey mode when operating the unit with a cable
connection to a PC and when high data rates are desired. Data can be logged
with a PC at rates up to 120 lines per minute (2 Hz).
Cyclic sampling: Use cyclic sampling to record data internally in the 8
Mb, non-volatile FLASH memory at regular intervals, e.g. every 1, 5, 15, or 30
minutes. Depending on the number of sensors measured and the statistics
selected, the OBS-3A can log as many as 200,000 lines of data (one per hour
for 23 years) including: time, date, depth, NTUs,
o C, and salinity.
1.11 Surveying
If you have a pressure sensor, click Bar. Corr. (do not do this when the
OBS-3A is submerged). The OBS-3A takes about five seconds to measure the
surface pressure and compute a barometric correction.
1. Connect OBS-3A to PC with survey cable.
2. Use to select: sensors, lines per minute, depth units (Meters or
Feet), water Temperature, and Salinity. Selection of temperature and
salinity only affects the depth calculation. It does not influence
temperature or salinity measurements.
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