Tokyo Keiki UFL-30, Installation & Operation Manual

Page: 163 / 166

III- 54
III-6-2. Measurement
The following is a description of some general problems and remedies relating to measurement.
If the steps shown in this section cannot solve a problem, contact Tokyo Keiki.
(1) Pipes which cannot be measured
• Asbestos
If the pipe surface is sufficiently wet, measurements can be made in some cases but generally is
difficult with this pipe material.
• Zinc coating pipe
Propagation of ultrasonic waves through the material itself is markedly poor and measurement is
generally difficult.
• FRPM
Ultrasonic wave attenuation through composite material is large with ø2000mm about the largest
measurable diameter based on our experience.
In addition composites vary according to the manufacturer. Therefore in cases of large
diameter pipes, pre-checks (i.e. to determine permeability of acoustic signals) should be carried
out.
- It is suggested that the portion of the piping at the measured location such as in the enclosure
or pit be changed to metal piping.
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• Pronounced scaling and rust on the inside of pipes causes attenuation and diffusion of acoustic
signals and the drop in transmission and receiving sensitivity sometimes makes measurement
impossible.
- In such cases, a better measurement location (for example an area where there is little rust)
might be found by shifting sensor positions which should improve signal reception. Care
should be exercised when doing this however as a narrower flow cross sectional area may
output results which are not true flow values.
(2) Fluids which cannot be measured
• The presence of continuous and large amounts of bubbles in the fluid will greatly attenuate
the acoustic signal, cause missed measurements, or make measurement impossible. Even
ultrasonic flowmeters employing the Doppler method which works better under such entrained
bubble conditions compared to transit-time flowmeters also encounter missed measurements or
are unable to make measurements when there is a continuous and large amount of bubbles
contained in the fluid being measured.
- If the cause of bubbles is a drop in level upstream, lessen the drop.
- When there is a layer of air in the pipe, install an air bleed valve forward of the measurement
location.
- Select measurement location where fluid contains few bubbles.