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FDT-25 Handheld Ultrasonic Flowmeter
* Patent balanced lower-voltage multi-pulse
* built-in date totalizers
ultrasonic igniting
* built-in data-logger
* Work properly near transverters
* 0.5 second totalizing period
* 100 Pico-second resolution of time measurement
§1.3 Principle of Measurement
The FDT-25 ultrasonic flow meter is designed to measure the fluid velocity of liquid within a closed
conduit. The transducers are a non-contacting, clamp-on type, which will provide benefits of non-
fouling operation and easy installation.
The FDT-25 transit time flow meter utilizes two transducers that function as both ultrasonic
transmitters and receivers. The transducers are clamped on the outside of a closed pipe at a specific
distance 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. This
selection of the mounting method depends on pipe and liquid characteristics. The 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 velocity
of the liquid in the pipe, as shown in Figure 1.
Downstream transducer
T
up
T
d
own
Flow
Where
0
is the include angle to the flow direction
M
is the travel times of the ultrasonic beam
D
is the pipe diameter
Spacing
Upstream transducer
Tup is the time for the beam from upstream transducer to the downstream one
Tdown is the time for the beam from downstream transducer to the upstream one
ΔT－Tup Tdown
