3 Measurement Principle FLUXUS G60x
UMFLUXUS_G6V4-2EN, 2011-03-29 15
3 Measurement Principle
3.1 Measurement System
With the clamp-on method, the ultrasonic transducers are mounted on the outside of the
pipe. Ultrasonic signals are sent through the medium and received by the transducers.
The transmitter controls the measuring cycle, eliminates the disturbance signals and an-
alyzes the useful signals. The received measured values can be displayed, used for cal-
culations and transmitted to a PC or printer by the transmitter.
3.2 Determination of the Volumetric Flow Rate
The flow velocity of the medium is measured using the transit time difference correlation
principle. Further physical quantities (e.g. volumetric flow rate, mass flow) are derived
from the flow velocity. The calculation is described below using the example of the volu-
metric flow rate.
The volumetric flow rate of the medium is calculated from the product of the flow velocity
and the cross-sectional pipe area:
= v
.
A
with
The signals are emitted and received by two transducers alternatively in and against the
flow direction. Because the medium moves, the signals propagating in the medium are
entrained. Their transit time in the flow direction is shorter than against the flow direction.
The transit time difference is proportional to the average flow velocity and therefore to the
volumetric flow rate.
Fig. 3.1: Example of a measurement setup
-
volumetric flow rate
v
-
flow velocity
A
-
cross-sectional pipe area
U L T R A S O N I C F L O W M E T E R
1 3
2
0
4 65
7
8
N E X T
Q
O N
Q -
Q +
M U X
D I S P
Q
O F F
L IG H T
E N T E R
C
O N
C H A N N E L A
C H A N N E L B
9
D I S P
E N T E R
3 x O F F
M O D E
B R K
B A T T E R Y
transducers
transmitter
pipe
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