Low Flow Suppression And Zero Alignment - Flow vision FC100 - CA User Manual

4 .3 .5 Low flow suppression and zero alignment

Low flow suppression
The low flow suppression serves to suppress small flow quantities and to detect leakages. The low
flow suppression option ranging from 1 to 10 % of the measuring range final value can be used to
eliminate false measurements as may arise upon (small) reverse flow quantities, for example. If flow
velocity is less than the value set, the flow velocity and the applicable flow is set at zero. This also
applies to all subsequent quantities such as analogue output and limit switches which are defined
in the other menus.
Zero alignment
Although because of its very special characteristic curve in the lower flow range the calorimetric
procedure implies a higher resolution than other measuring procedures, it is not possible to exactly
measure zero flow. The reason for this is that in the lower flow range (<1 % of measuring range final
value) current flow is superimposed by convection flow around the heated monitoring head sensor.
Convection flow is very difficult to theoretically detect for all measuring systems (monitoring head and
FC100-CA); it is determined by installation, current pressure, temperature, etc..
To ensure correct zero alignment, the pipeline should be operated under the desired pressure and
temperature conditions. A waiting period of approx. 2 ... 5 minutes should be observed after the pipe
system has been closed (zero volume flow) to ensure correct alignment. If the FC100-CA indicates flow
after pipeline has been opened, there is definitely flow available.
To start zero alignment MIN. FLOW = 00% has to be selected in submenus ZERO SUPPRESSION.
After this adjustment even smallest volume flow quantities can be reliably indicated.
Caution!
No plausibility test to ensure there is no volume flow is conducted for zero alignment. The
volume flow available at that time is set at zero. This should be considered above all for untight
valves. In this case the zero volume flow determined this way may even be greater than 1 %.
Accuracy in the lower measuring range will decrease then. To be on the safe side, the lower
limit should therefore be set at 1 % if no reliable zero adjustment can be made.
FC100-CA | Flow Meter
OPERATION AND MAIN MENU
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