Flexim FLUXUS G704, User Manual, Page: 25 / 257

UMG70XV3-4EN 12.01.2009 25
4 Flowmeter
4 Flowmeter
4.1 Measuring Principle
The flow of the medium is measured by ultrasonic signals using the transit time differ-
ence method.
Ultrasonic signals are emitted by a transducer installed on one side of a pipe, reflected
on the opposite side and received by a second transducer. The signals are emitted alter-
natively in and against the flow direction.
As the medium in which the signals propagate is flowing, their transit time in flow direc-
tion is shorter than against the flow direction.
The transit time difference

t is measured allowing to determine the average flow velocity
on the propagation path of the ultrasonic signals. A flow profile correction is then per-
formed to obtain the area average of the flow velocity, which is proportional to the volume
flow.
The received ultrasonic signals will be tested for usefulness for the measurement and the
plausibility of the measured values will be evaluated. The complete measuring procedure
will be controlled by the integrated microprocessors. Disturbance signals will be eliminat-
ed.
Fig. 4.1: Path of the ultrasonic signal
Fig. 4.2: Transit time difference

t