ADS Environmental Services Model 3600 530002 A2 - Manual (Page 30)

Flow Measurement 3-5
recorded by one of two temperature sensors mounted inside the ultrasonic depth
sensor.
Enhanced firmware (permanently stored software) for the ultrasonic level sensor has
been added to the 3600 monitor to increase its capabilities. While the appearance and
composition of the ultrasonic level sensor is unchanged, this firmware stores an
algorithm that allows the updated sensor to filter out noise caused by bad signals that
return from the apron, side connections, rungs, broken pipes, or drop connections.
With previous sensor data, the data analyst was required to examine and filter out
noise readings that occurred when a sensor was not working properly. Now, the 3600
monitor uses this improved algorithm to filter out bad signals automatically. It also
produces more accurate data, yields one final average, and decreases the amount of
data that has to be stored.
Basically, each time the monitor fires the sensors and takes a reading, the algorithm
triggers two separate processes. First, the algorithm automatically determines a range
window, or set of standards, for good return echoes. The analog return signal is
digitized, and the sensor fires all 12 pairs five times each for a total of 60 firings. (In
earlier depth sensor design, only four pairs were fired.) The algorithm then takes an
average of the pairs to use in determining the range. The range is set by scanning
through the digital data and recording the strongest returning echoes, and a range
window is created around these echoes. Thereafter, the sensor accepts echoes only
within that range; bad signals are screened out.
Second, the monitor uses the standards set by the algorithm in the first sensor firing to
process the return echoes and determine the range actually used to record depth of
flow in the pipe. The monitor fires the sensors, which take 32 analog readings of each
of the 12 pairs (384 firings) because the analog signals produce a greater resolution
and are more accurate. The range window is then applied to each of the 32 readings,
and the signals outside of that window are screened out; this process is called
scrubbing. Interpair and intrapair averages are taken; the scrubbing routine is applied
again, and the algorithm produces one final range. In order to save memory space,
this single range is stored in memory rather than the four ranges used in previous
designs.
Pressure Depth Sensor
The pressure depth sensor, or pressure mouse, is typically placed at the bottom of the
pipe. This depth sensor can measure depths greater than full pipe (surcharges),
whereas the ultrasonic depth sensor only measures depths up to full pipe capacity.
The pressure sensor contains a differential pressure transducer which transmits an
output voltage corresponding to the difference between the water pressure and the air
pressure in the sewer. Water pressure is measured through a port on the underside of
the pressure sensor. Air pressure is measured using an integral vent tube which runs
to the top of the manhole. By reading the difference in pressures, the depth board