Tokyo Keiki UFP-20, Руководство по установке и эксплуатации

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(3) Given measurement accuracy cannot be obtained
• Incorrect site condition
Check pipe specification.
• Insufficient straight pipe length
Required straight pipe length may vary according to changes in pipe conditions forward and
backward of the measurement position (merged or separating flows, presence of valve, etc.).
Refer to Chapter “ 1.2.5 Selection of transducer setup position (p.1-26)”.
• Inside pipe condition
Cause may also be attributable to changes in fluid cross sectional area due to pipe rust,
scale and partially filled pipe conditions. Refer to Chapter “ 1.2.5 Selection of transducer
setup position (p.1-26)”.
• Seam part of pipe
It may cause seam part to make un-expected reflection of ultrasonic. Select no-seam part
for transducer installation. Please refer to Chapter “ 1.2.5 Selection of transducer setup
position (p.1-26)”.
(4) Measurement values are unstable
• Entrained bubbles or solid particles in the fluid
It may cause fluctuation or spikes in measurements or create non-measurable conditions.
Please eliminate the sources of these problems.
• Cavitation occurs.
Cavitation sometimes occurs when butterfly valves are used.
When there is cavitation from entrained air, select a measurement position sufficiently
distanced from such locations and where the bubble problem ceases to exist.
• External noise
Electrical signals received by ultrasonic flowmeters 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 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.
In case of metal pipe application, small or medium transducer must be insulated from the
pipe electrically. Some of the stronger noise like coming from invertors may not be avoidable.
Using extension cable is also conductive to get noise influence.
(5) Echo is received, but no fluid inside.
• Ultrasonic transmits through the pipe wall surface
In case of some of the conditions which related with pipe material, pipe diameter or
transducer installation method, the ultrasonic may transmit on the pipe wall surface.
When the location of surface echo is very near-by proper echo point, main unit may not be
able to clarify between proper echo and surface echo. Therefore, it might not be able to be
judged no echo receiving.
When the transducer installation method is changed, it could be possible to avoid this.
A similar phenomenon might be shown in PVC lining steel pipe which may contain air layer
between metal and lining, even if there is a fluid. Refer to “ (1) Pipes which cannot be
measured (p.3-31)”.