SICK FLOWSIC200, Руководство по эксплуатации

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Product description
FLOWSIC200 · Operating Instructions · 8013271/1CJ9/V2-0/2022-01 · © SICK Engineering GmbH 17
Determining the flow velocity
Measuring path L is equal to the active measuring distance, that is, the free flowing
distance. Given measuring path L, sound velocity c, and angle of inclination

between the
sound and flow direction, the following applies for the transit time of the sound when sound
is emitted in flow direction (forward direction):
(2.1)
Valid against the flow is:
(2.2)
The resolution to v gives:
(2.3)
A relation in which, apart from the two measured transit times, only the active measuring
distance and the angle of inclination are constants.
Determining the air temperature
The temperature dependency of the sound velocity allows using the calculated transit times
to determine the air temperature.
Simultaneous detection of flow velocity and temperature can be used to warn of icy
conditions when the road surface is wet and temperatures are below or around freezing
point.
The sound velocity is obtained by resolving to c:
(2.4)
For the temperature dependence of the sound velocity, the following applies with standard
sound velocity c
0
at 0 ° C (= 331.4 m/s) and air temperature

in ° C:
(2.5)
This results in the following for the air temperature:
(2.6)
Formula 2.6 shows that the determined temperature depends not only on the measured
transit times but also quadratically on the measuring distance and the standard sound
velocity
.
This means precise temperature measurement is only possible when
measuring distance L has been determined very accurately and a calibration
has been carried out (

p. 92, §4.3.3 2 ) and the air composition is constant.
c = ·
( )
L t
v
+ t
r
2 t
v
· t
r
c = c
0
· 1 +

273 ° C

= 273 °C ·
(
·
( )
- 1
)
L
²
t
v
+ t
r
4 · c
0
²
t
v
· t
r
t
v
=
L
c + v · cos

t
r
=
L
c - v · cos

v = ·
( )
L 1 1
2 · cos

t
v
t
r