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FLOWSIC30 · Operating Instructions · 8020999/173B/V1-4/2020-02 · © SICK Engineering GmbH
Product description
Su
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2.1
Functional principle
The FLOWSIC30 works according to the principle of ultrasonic transit time difference
measurement. Measured signal travel times t
AB
and t
BA
are defined by the current sound
and flow velocity of the gas.
Gas velocity v is determined from the difference between the signal travel times. Therefore
changes in the sound velocity caused by pressure or temperature fluctuations do not affect
the calculated gas flow rate with this method of measurement.
Fig. 3
Measuring principle FLOWSIC30
2.2
Calculations
2.2.1
Determining the gas velocity
Measuring path L is equal to the active measuring path, that is, the area through which the
gas flows. Given measuring path L, sound velocity c, and angle of inclination α between the
sound and flow direction, the sound transit time in the direction of the gas flow (forward
direction) when the signal is transmitted can be expressed as:
i.e. a relation in which, except for the two transit times measured, only the active measuring
path and the path angle exist as constants.
Ultrasonic transducer B
Ultrasonic transducer A
t
BA
v
Meter body
L
t
AB
v
= Gas velocity in m/s
L
= Measuring path in m
= Angle of inclination in °
t
AB
= Sound transit time in flow direction
t
BA
= Sound transit time against the flow
direction
Valid against the flow is:
After the resolution to v:
v =
· (
)
t
BA
=
t
AB
=
L
1 1
2 · cos α
t
AB
t
BA
L
c - v · cos α
L
c + v · cos α
(2.1)
(2.2)
(2.3)
