10 Troubleshooting
FLUXUS H721
10.2 Measuring point selection
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UMFLUXUS_H721V1-5EN, 2022-05-15
10.2
Measuring point selection
• Make sure that the recommended min. distance to any disturbance 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.
• A vertical pipe always has to be filled at the measuring point and 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 may not be determined
correctly.
• The fluid sound speed is used to calculate the transducer distance and is therefore very important for the transducer
positioning. The sound speeds stored in the transmitter only serve as an orientation.
The entered pipe roughness is not appropriate.
• Check the entered value considering the pipe condition.
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 an acoustically absorbing material.
• Try to measure on a section of the pipe free from lining.
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, a pipe wall signal can be mistaken for the
measuring signal. The flow calculated by the transmitter on the basis of the wrong signal is very small or fluctuates
around zero.
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
deviated 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).
The entered pipe roughness is not appropriate.
The flow velocity of the fluid is outside the measuring range of the transmitter.
The measuring point is not appropriate.
• Check whether a different measuring point provides better results. Because pipes are never rotationally symmetric and
the flow profile is affected.
