Description; Measuring Principle - Siemens SITRANS F Series Operating Instructions Manual

Description

SITRANS F US ultrasonic flowmeters measure flow in standard volumetric units. Measurement
is independent of changes in liquid temperature, density, pressure and conductivity. A time of
flight flowmeter is designed for use on single phase liquids.
They are designed for measurement of:
● Volume flow rate
● Limit monitoring
● Total volume
● Sound velocity in the media
3.1

Measuring principle

Physical principle
Figure 3-1
A sound wave travelling in the same direction as the liquid flow arrives at point B from point A
in a shorter time than the sound wave travelling against the direction of flow (from point B to A).
The difference in sound transit time indicates the flow velocity in the pipe.
Since delay time is measured at short intervals both in and against flow direction, temperature
has no influence on measurement accuracy.
SITRANS F US flowmeters
In SITRANS F US flowmeters the ultrasonic transducers are placed at an angle θ in relation to
the pipe axis. The transducers function as transmitters and receivers of the ultrasonic signals.
Measurement is performed by determining the time the ultrasonic signal takes to travel with and
against the flow. The principle can be expressed as follows:
v
v
SITRANS F US SONO 3300
Operating Instructions, 01/2010, SFIDK.PS.029.J4.02
Velocity distribution along sound path
= K × (t – t ) / (t
B,A A,B
= Average flow velocity
× t ) = K × Δt/t²
A,B B,A
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