26
ECNO: 622
7. Q & A
7.14 What is the difference between a Doppler type
flowmeter and PORTAFLOW X?
A Doppler type flowmeter emitts ultrasonic waves and receives the waves reflected from foreign
objects in the fluid.
Velocity is measured utilizing the principle that the frequency deviation of the received waves from
the emitted ones is in proportion to the flow velocity (Doppler effect).
Therefore:
(1)
The fluid must contain foreign objects (including air bubbles). It is not suited for clean water
but is suited for sewage.
(2)
Since the position in the fluid where the reflection occurs is obscure, the amount and nature of
foreign objects in the fluid affect the measuring accuracy together with the velocity profile in
the piping.
PORTAFLOW X is designed to measure the velocity with ultrasonic waves passing through piping.
As it measures an average velocity in the piping, it measures flow rate highly accurately.
The Doppler system has the above-mentioned disadvantage, but it is used to measure an approxi-
mate flow from the outside of the piping, permitts liquids with large amount of foreign objects, and
is effectively used for liquids with slurry or air bubbles.
7.15 Life span of LCD
The life span of LCD is considered to be about l0 years under general operating conditions, ac-
cording to the manufacturer’s catalogue. Generally, it is about 5 to 6 years in actual service.
The life span is not so much related to the number of displaying operations.
