Flexim FLUXUS WD, Operating Instruction

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10 Troubleshooting
10.2 Measuring point selection
FLUXUS WD
2018-07-16, UMFLUXUS_WDV1-3EN
96
10.2 Measuring point selection
• Make sure that the recommended min. distance to any disturbance source is observed.
• Avoid measuring points with deposit formation in the pipe.
• Avoid measuring points in the vicinity of deformations and defects on the pipe as well as welds.
• Make sure the pipe surface at the selected measuring point is even.
• Measure the temperature at the measuring point and make sure that the transducers are suitable for this temperature.
• Make sure that the outer pipe diameter is within the measuring range of the transducers.
• When measuring on a horizontal pipe, the transducers have to be mounted laterally on the pipe.
• The measuring point on a vertically mounted pipe has always to be filled. The fluid should flow upward.
• No gas bubbles should form (even bubble-free fluids can form gas bubbles when the fluid expands, e.g., upstream of
pumps and downstream of great cross-section enlargements).
10.3 Maximum acoustic contact
see section 6.2
10.4 Application-specific problems
A fluid with a wrong sound speed was selected
If the selected sound speed in the fluid does not match the actual one, the transducer distance can probably not be deter-
mined correctly.
The fluid sound speed is used to calculate the transducer distance and is therefore very important for the transducer posi-
tioning. The sound speeds stored in the transmitter only serve as an orientation.
The entered pipe roughness is not appropriate
Check the entered value. The pipe state should be considered.
Measurements on pipes made of porous materials (e.g., concrete or cast iron) are only conditionally possible
Contact FLEXIM.
The pipe lining may cause problems during the measurement if it is not firmly attached to the inner pipe wall or
consists of acoustically absorbing material
Try to measure on a section of the pipe free from lining.
Highly viscous fluids strongly attenuate the ultrasonic signal
The measurement of fluids with a viscosity of > 1 000 mm²/s is only conditionally possible.
A high concentration of gases or solids in the fluid scatter and absorb the ultrasonic signal and thus attenuate
the measuring signal
A measurement is impossible if the value is ≥ 10 %. If the proportion is high, but < 10 %, a measurement is only condition-
ally possible.
10.5 Significant deviations of the measured values
A fluid with a wrong sound speed was selected
If a fluid was selected whose sound speed does not match the actual one, the measuring signal may be confused with the
pipe wall signal.
The flow calculated on the basis of the wrong signal by the transmitter is very small or fluctuates around zero.
There is gas in the pipe
If there is gas in the pipe, the measured flow will be too high because both, the liquid and gas volume, are measured.
The defined upper limit of the flow velocity is too low
All measured flow velocities that are greater than the upper limit will be ignored and marked as invalid. All quantities devi-
ated from the flow velocity will also be indicated as invalid. If several correct measured values are ignored, the totalizer
values will be too low.
The entered cut-off flow is too high
All flow velocities below the cut-off flow are set to zero. All derived quantities are also set to zero. The cut-off flow has to be
set to a low value to be able to measure at low flow velocities (default: 2.5 cm/s).