Operating Instructions FLOWSIC100
Gas Velocity Monitor
Product Description
8012513/03-2008 © SICK MAIHAK GmbH · Germany · All rights reserved 17
2.2.3 Operating Principle
The FLOWSIC100 gas velocity monitors operate by measuring the transit time difference of
ultrasonic pulses. Sender/receiver units are mounted on both sides of a duct/pipeline at a
certain angle to the gas flow (Fig. 2.4).
These sender/receiver units contain piezoelectric ultrasonic transducers that function
alternately as senders and receivers. The sound pulses are emitted at an angle α to the flow
direction of the gas. Depending on the angle α and the gas velocity v, the transit time of the
respective sound direction varies as a result of certain "acceleration and braking effects"
(formulas 2.1 and 2.2). The difference in the transit times of the sound pulses increases,
the higher the gas velocity and the smaller the angle to the flow direction is.
The gas velocity v is calculated from the difference between both transit times, independent
of the sound velocity. Changes in the sound velocity caused by pressure or temperature
fluctuations, therefore, do not affect the calculated gas velocity with this method of
measurement.
Fig. 2.4: Operating principle of the FLOWSIC100
v = gas velocity in m/s
L= measuring distance in m
α = angle of inclination in °
t
v
= signal transit time in the
direction of the gas flow
t
r
= signal transit time in the
direction opposite the gas
flow
Sender/receiver unit slave
Sender/
receiver
unit master
t
v
v
α
t
r
L
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