Ultraflux UF 831, Руководство пользователя, Страница: 52 / 109

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NT UF 831 CO GB (b) / March 2014
3) Calibration (CutOff Q)
The deletion rate is the flow value below which the flow meter will display 0. This will provide you with a
clear indication of a flow considered as null.
4) Immersion depth of the probes
For it to be possible for the velocity measured by a chord to be included in the flow calculation, the chord
must be sufficiently immersed so as not to suffer disturbances created by the trough of the wavelets or for
there to be no interference between the direct path of the ultrasonic wave and the path of the wave
reflected by the surface.
If the signal generated by the reflected wave follows the signal generated by the direct wave too closely, the
wanted signal may be appreciably altered by the secondary signal. It may even almost disappear if there is
phase opposition between the two signals. The minimum immersion depth of the probes below which the
measured velocity is considered invalid must therefore be indicated. This minimum immersion depends on
the frequency used and the length of the acoustic path.
Comment: The immersion depth of the probes is counted from the central plane of a chord.
5) Weighting coefficients of the chords (coef chord)
A weighting coefficient is a corrective factor and is applied when calculating the velocity. For example, if you
wish to reduce the velocity of a chord by 10%, a coefficient of 0.9 must be entered.
6) Delta T0
The delta T0 field is used to correct installation errors. For example, it is possible to compensate for a bias
due to an incorrect position of the probes by adding to delta T0 the value required in order to rectify it.
7) Vmin and Vmax
In certain situations, the velocity of the fluid measured by the flow meter may be disrupted. Limits can then
be set for the velocity of the fluid using a minimum velocity and a maximum velocity.