Euromag EUROSONIC 2000 HH, User Manual

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8 | EUROMAG
EUROSONIC 2000 HH
1.3 FLOW MEASUREMENT PRINCIPLE
The hand held flow meter ultrasonic flow meter is
designed to measure the velocity of liquid within a
closed conduit. It uses the well-know transit-time
technology. The transducers are a non-contacting,
clamp-on type. They do not block the flow, thus no
pressure drop. They are easy to install and remove.
The hand held flow meter utilizes a pair of transducers
that work as both ultrasonic transmitter and receiver.
The transducers are clamped on the outside of a
closed pipe at a specific distance one from each other.
The transducers can be mounted in V-method where
the sound transverses the pipe twice, or W-method
where the sound transverses the pipe four times, or
in Z-method where the transducers are mounted on
opposite sides of the pipe and the sound crosses the
pipe once. The selection of the mounting methods
depends on pipe and liquid characteristics.
The hand held flow meter operates by alternately
transmitting and receiving a frequency-modulated
burst of sound energy between the two transducers
and measuring the transit time that it takes for sound
to travel between the two transducers. The difference
in the transit time measured is directly and exactly
related to the liquid speed, as shown in the following
figure.
TRANSIT TIME FLOW MEASUREMENT PRINCIPLE
V = x
MD
sin 2Ø
∆T
T
up
• T
down
O
SPACING
DOWNSTREAM TRANSDUCER
UPSTREAM TRANSDUCER
FLOW
T
up
T
down
REFERENCES
Ø
is the angle between the sound path and the flow direction
M
is the number of times the sound traverses the flow
D
is the pipe diameter
T
up
is the time for the beam travelling from upstream the
transducer to the downstream transducer
T
down
is the time for the beam travelling from the downstream
transducer to the upstream transducer
∆T = T
up
– T
down
f. 1