Aalborg PWE Digital - Manual (Page 49)

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4.9 Submenu Flow Meter Configuration
4.9.1 Submenu Flow Meter Low Flow Cut–off
Numerical entry
The low flow cut-off can be selected between 0.0 and 10.0 % of the full scale
range. Flows less than the cut-off value are internally driven to zero and not total-
ized. The analog 0-5 vdc or 4-20mA current outputs are set to 0.0 Vdc and 4.00
mA correspondently. The switching threshold for the low flow cut-off has 1.0
%F.S. hysteresis. A typical display with Low Flow Cut–off selection is shown
below.
4.9.2 Submenu Pulse Number Measure Interval
Numerical entry
Signal Processing software algorithm can be set to calculate flow rate based on
two different methods (see Section 4.9.4):
a) number of pulses over preset measure interval
b) pulse width measurement
Both methods calculates frequency of the pulses from the flow meter sensor. The
number of pulses over preset measure interval method convenient when pulsat-
ing flow or especially noisy signals are encountered.
This method allows to get stable average flow rate if pulse measure interval is set
to values more than 4000 ms. This parameters effects the flow update rate. With
higher value of the pulse measure interval, the resolution and stability of the flow
measurement improves, but response time become longer. A suggested pulse
measure interval value of 4000 seconds is a good starting point for most applica-
ble process fluids. With lower settings the response time of the meter will be
shorter, but resolution and stability will degrade.
The pulse measure interval settings are only related to the number of pulses over
preset measure interval method. Pulse measure interval can be selected between
500 and 60000 ms. A typical display with pulse measure interval selection is
shown below.
Low Flow Cut–off
1.000 %F.S.