Tokyo Keiki UFL-30, Installation & Operation Manual

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(3) Given measurement accuracy cannot be obtained
- Check pipe specification.
• Insufficient straight pipe length
- Required straight pipe length may vary according to changes in pipe conditions forward and aft
of the measurement position (merged or separating flows, presence of valve, etc.)
- Distortions in fluid velocity distribution may be exacerbated by insufficient straight pipe lengths
which adversely influence measurement resulting in poor accuracy.
In such cases employing multi-path measurement reduces the affect of such distortions in fluid
velocity distribution.
• Cause may also be attributable to changes in fluid cross sectional area due to pipe rust
and scale and partially filled pipe conditions.
(4) Measurement values are unstable
• Entrained bubbles or solid particles in the fluid may cause fluctuation or spikes in measurements
or create non-measurable conditions.
- Eliminate the sources of these problems.
• Cavitation occurs.
Cavitation sometimes occurs when butterfly valves are used (except for butterfly valves specially
designed to prevent cavitation).
- When there is cavitation from entrained air, select a measurement position sufficiently
distanced from such locations and where the bubble problem ceases to exist.
• Exogenous noise
Electrical signals received by ultrasonic flowmeters are generally are very weak - in the order of a
few mV’s - and as such ultrasonic flowmeters are susceptible to power surges and noises.
- When there is the possibility of external noise interference on ultrasonic flowmeter measurement,
check the layout and the grounding of each cable. In the case of noise intrusion (especially
on sensor cables) from an AC power source, installation of a shielded transformer, etc., is
effective. However the high magnitude of noise interference from inverters sometimes
invalidates such countermeasures.