ADS Environmental Services Model 4000 530017 A0 - Manual (Page 21)

System Overview 2-9
The monitor discards the clearly erroneous readings (i.e.,
readings well outside the range of the majority of the
readings).
The monitor records the percentage of all acceptable readings
used to arrive at the average value.
Secondary scrubbing also can occur during data collection from the
monitor to the analyst's PC using the Profile software. Refer to the
Profile User's Guide (950015**) for more information.
Standard Ultrasonic Depth
The standard method for processing ultrasonic depth involves firing
the sensor once to take 32 readings for each of the 4 user-defined
transducer pairs. The monitor discards all false and multiple
echoes and then averages the good readings to arrive at the final
reading for each pair. It then logs each of the 4 pairs.
Smart Depth
The 4000 also includes an enhanced algorithm in the firmware
(permanently stored software), which can be enabled by the user,
for processing ultrasonic depth that automatically filters out bad
signals or erroneous readings due to flow problems or obstructions.
This process produces more accurate data, yields one final depth
measurement, and reduces the amount of stored data. It also
significantly decreases the need for manual analysis and editing.
Each time the monitor fires the sensor to take a reading, the
algorithm triggers two separate processes. First, the algorithm
automatically determines a set of standards, or range window, for
good return echoes. It accomplishes this by digitizing the analog
return signals and firing all 12 transducer pairs 5 times each (60
total firings). Then, an average is taken of the pairs to determine
the range. The range is set by scanning through the digital data and
recording the strongest returning echoes. A range window is
created around these echoes. From that point forward, the monitor
accepts echoes only from within that range and screens out the bad
signals.