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22.0 About real time data - continued
If the operator is receiving data such as displayed in the diagram above,
the sensor may be moved slightly to try to overcome the distortion.
Furthermore, the operator should inspect the positioning of the sensor to
ensure that there is not a build-up of debris or other matter, close to the
sensor head. If no obstruction is observed and re-positioning the sensor
does not improve the data, you can be assured that the sensor is operating
effectively and that the displayed data is a site induced phenomenon.
Factors affecting the velocity sensor
This section is designed to give the operator a brief understanding of some of
the factors affecting the performance of the MACE Flo-Series velocity sensor.
In flowing streams, there are always a range of different velocities present,
particularly in turbulent water where the effects of eddies and boundary
layers can cause the velocity histogram to appear distorted in the diagram
below. Although distorted, MACE Flo-Series instruments have powerful
signal processing algorithms, which determine the average stream velocity
from these signals.
58 Section b SOFTware Manual
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If data such as that seen above is received, the operator should ensure that
the sensor is positioned correctly and monitor the site for any obstructions
close to the sensor. If no obstructions are located close to the sensor, the
site may be unsuitable to flow measurement with Doppler ultrasonic flow
devices.
The signal strength of received echoes on the real-time histograms, is
a measure of the number of reflective particles moving in the stream.
Therefore, low signal strengths do not necessarily equate to poor velocity
readings. Relatively few particles may provide enough echoes for an accurate
average velocity reading. Furthermore, a histogram with a broad base will
generally tend to have a peak with a lower signal strength. In sites where it
is suspected that there are relatively few reflective particles in the flow, the
period in which the MACE Flo-Series instrument takes readings may require
extending (see, Velocity integration period).
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Mace Agriflo Series3 Product Manual
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