Mace HVFlo XCi, Product Manual

Page: 162 / 255

In the figure above signal noise can be seen on the velocity spectrum graph as low signal strength
echoes. In the graph above you can see that the signal noise has an approximate amplitude value of 75.
Therefore, by setting a threshold of say 100, this noise will be ignored in the computation of average
velocity. The user should be careful however, at sites where signal strength is inherently lower, a peak
threshold that is set too high could mean that true velocity readings are discarded.
This feature is particularly useful at sites where the sensor may be submerged for periods where no flow is
occurring. For example, signal noise encountered in a submerged 1 m diameter pipeline that gives a false
“average velocity” of 1 m/s will still increase a totalising counter by 785 litres per second, even though no true
flow existed. By watching several real-time graphs of no flow conditions and monitoring the extent of signal
noise apparent, a peak threshold may be set so that signal noise is not computed as real flow.
Correction factor
Unfortunately, ideal hydraulic conditions cannot be achieved at every site that requires monitoring. In
locations where hydraulic conditions are such that velocity calibrations at various flow regimes are required,
then the “ Correction factor ” may help. Under abnormal hydraulic conditions, the average velocity of the
stream must be calculated using traditional means that comply with Australian (refer to AS3778 series) or
International Standards (refer to ISO772).
WARNING: The velocity correction factor can be set to scale the calculated velocity
result and should only be used with extreme care
It allows a single multiplication factor to be applied to the calculated velocity readings.
For example, should a trusted primary source of flow measurement show that the XCi device is under-
reading by 5%, then the correction factor should be set to 1.05. If it is proven to be over-reading by 5% then
the correction factor should be set to 0.95.
"Sensor settings"
Clicking on " Sensor settings " will open up the " Doppler sensor options " dialogue box. The only available
function is the ability to change the " Pipe diameter " or " Cross-sectional area ". All other settings are
"greyed out".
MACE XCi User Manual - 162 -