Emerson Flexim FLUXUS G722ST-HT Operating Instruction page 12

3 General principles
3.1 Measurement principle
3.1.2 Measurement of the flow velocity
The flow velocity of the fluid is measured using the correlation principle. 2 pairs of ultrasonic transducers of the same type
are mounted one after the other at a distance Δx on the pipe which is completely filled with the fluid. The transducer pairs
form the measuring barriers A and B. Ultrasonic signals are alternately emitted by the emitters A
the respective receivers A
2
turbulent flowing fluid. Since the swirls move with the flow, they pass the measuring barriers A and B with a time offset Δt, so
that the modulation patterns of the ultrasonic signals of measuring barrier A and B are also offset by Δt. This time offset Δt is
measured by means of cross correlation of the modulation signals. The average flow velocity can be calculated using the
fluid mechanic calibration factor.
x
v = k · ------ -
Re
t
where
v – average flow velocity of the fluid
k – fluid mechanic calibration factor
Re
Δx – distance between the measuring barriers
Δt – time offset of the modulation patterns
Fig. 3.1: Measurement arrangement of the correlation principle
A
1
A – emitter of measuring barrier A
1
A – receiver of measuring barrier A
2
B – emitter of measuring barrier B
1
B – receiver of measuring barrier B
2
Δx – distance between measuring barriers
Fig. 3.2: Time offset of the modulation signals Δt
A – modulation signal of measuring barrier A
B – modulation signal of measuring barrier B
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and B . The ultrasonic signals are modulated regarding amplitude and phase by the swirls of the
2
Δx
B
1
flow direction
of the fluid
A B
2 2
A
B
Δt
time
FLUXUS G722ST-HT
and B and received by
1 1
2024-03-01, UMFLUXUS_G722ST-HTV2-2EN