Dwyer UFM - Manual (Page 5)

F - UFM
Issue 1.4 Page 5
2
How does it work?
The UFM is a clamp-on, ultrasonic flowmeter that uses a multiple slope transit time algorithm
to provide accurate flow measurements.
An ultrasonic beam of a given frequency is generated by applying a repetitive voltage pulse to
the transducer crystals. This transmission goes first from the Downstream transducer to the
Upstream transducer (red) as shown in the upper half of Figure 1. The transmission is then
made in the reverse direction, being sent from the Upstream transducer (red) to the
Downstream transducer (blue) as shown in the lower half of Figure 1. The speed at which the
ultrasound is transmitted through the liquid is accelerated slightly by the velocity of the liquid
through the pipe. The subsequent time difference T1
– T2 is directly proportional to the liquid
flow velocity.
Figure 1 Principle of Transit-Time operation