GE AquaTrans AT600, User Manual

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Chapter 1. General Installation Instructions
2 AquaTrans™ AT600 User’s Manual
1.2 Theory of Operation
The AT600 flow meter uses a procedure called
Transit-Time Flow Measurement
. In this method, two
transducers, which are in acoustic communication with each other, serve as both ultrasonic signal
generators and receivers. That is, the second transducer can receive ultrasonic signals transmitted by the
first transducer and vice versa.
In operation, each transducer functions as a transmitter, generating a certain number of acoustic pulses, and
then as a receiver for an identical number of pulses (see
Figure 2 and Figure 3 below). The time interval
between transmission and reception of the ultrasonic signals is measured in both directions. When the
liquid in the pipe is not flowing, the transit-time downstream equals the transit-time upstream. However,
when the liquid is flowing, the transit-time downstream is less than the transit-time upstream. The
difference between the downstream and upstream transit times is proportional to the velocity of the flowing
liquid and its sign indicates the direction of flow.
Figure 2: Flow and Transducer Paths (Two Traverses)
Figure 3: Flow and Transducer Paths (One Traverse)