Teledyne ULTRAFLOW 150, Operation Manual, Page: 19 / 162

SECTION 4.0, Theory of operation
4.0 THEORY OF OPERATION
4.1 PHYSICS OF MEASUREMENT
4.1.1 Time of Flight Theory
The Ultraflow 150 system measures the transit times of ultrasonic tone bursts
through the gas stream to determine flow velocity, temperature, and volume.
Each effluent path monitored by the Transducer Interface Enclosure (TIE) uses
two transducers placed on opposite sides of the stack or duct (see Ultraflow 150
System Installation Drawing, Appendix D). The transducers are pointed at each
other with one transducer located diagonally upstream from the other. Each
transducer acts alternately as a transmitter or receiver with the ultrasonic waves
passing through the centroid of the stack or duct to the other transducer. This
makes the measurements a line average of the tone burst path length. When a
tone burst is sent through the gas stream from the upstream transducer to the
downstream transducer the movement of the gas stream reduces the time required
to traverse the distance. When the tone burst is traveling against the gas stream
from the downstream to the upstream transducer, the traverse time is increased.
When there is no gas flow, the time required for the ultrasonic tone bursts to
traverse the gas stream in either direction is the same. Both the upstream and
downstream transit times are measured by the Transducer Interface Enclosure to
an accuracy of 0.5 microseconds.
Figure 4-1
Transit Time Theory
Upstream
Transducer
L
θ
(Actual)
Fv
(Nominal)
Fv
Ft
Downstream
Transducer
4-1