GE PanaFlow HT, Руководство пользователя

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Chapter 1. Introduction
2 PanaFlow HT User’s Manual
1.2 Theory of Operation
1.2.1 Transit-Time Flow Measurement
In this method, two transducers serve as both ultrasonic signal generators and receivers. They are in acoustic
communication with each other, meaning 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. 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. 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
1.2.2 Active Temperature Compensation
Ultrasonic flowmeters use transit time to determine the liquid or gas flow in a pipeline.
Measured transit time consists not only of the time the ultrasonic signal spends in a fluid, but also of a portion of “dead
time,” being the time that the electrical signal is converted into an acoustical signal and the time the acoustic signal
travels inside the transducer.
To allow for the utmost accuracy, PanaFlow HT uses pulse echo to actively measure the dead time. By sending a pulse
and measuring its reflection, the dead time is measured in real time rather than using a preset value. As a result of this
GE invention, PanaFlow HT maintains its accuracy as process temperature conditions dynamically change.