Description
3.4 Principle of operation
SITRANS FUS080 transmitter
Operating Instructions, 07/2012, A5E03059912-02
17
● Factory preset to the nominal dimensions of pipe type and pipe size
● Manual programming of mechanical/geometrical pipe data via SIMATIC PDM
● Local control panel with single push button, 8-digit display and IrDA optical interface for
communication with SIMATIC PDM
● Display showing accumulated volume as well as instantaneous flow rate. The displayed
units are m
3
/h and m
3
● Two digital outputs for volume pulse or alarm
● Optional field bus communication module (MODBUS RTU) for direct communication with
a PLC/RTU. Recommended use of such options are with mains-powered versions.
3.4
Principle of operation
Physical principle
Figure 3-2
Velocity distribution along sound path
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 = K × (t
B,A
– t
A,B
) / (t
A,B
× t
B,A
) = K × Δt/t²
where
v = Average flow velocity
t = Transit time
K = Proportional flow factor