[The ultrasonic flow meter is a device providing determination of the fluid flow rate…]
Devices for measuring the flow of the transported medium parameters are applied in main and linear pipelines. The ultrasonic flow meter is a device providing determination of the flow rate of fluids and gases. The principle of such a measuring system operation is based on the laws of propagation of acoustic vibrations in a flowing medium.
The device is used to determine the volume flow of fluids or gases with a set accuracy for a long time or with a certain periodicity. The flow meter uses acoustic vibrations of the ultrasonic range with a frequency of more than 20 kHz. They are not perceived by human hearing organs, but are widely used in echolocation.
The physical fundamentals of the principle of flow meter operation
Acoustic vibrations occur in a gas, fluid or solid medium as a result of vibrations of the sound source. As a result, a sound wave is formed, the parameters of which depend on several factors as follows:
— specific density;
— temperature;
— medium structure (uniformity).
The most important sound wave parameters include frequency, length and amplitude. The first is defined as the number of vibrations per unit of time and is measured in Hertz. The ultrasonic range in which the described flow meters operate consists of frequencies from 20 kHz to 100 MHz. Such vibrations are perceived only by some animals, for example, dolphins and whales, as well as bats.
The control electrical signal entering one of the transceivers is converted into mechanical vibratory energy (reverse piezoelectric effect), creating acoustic vibrations in the measured operating medium. The vibrations are received by another transceiver from the pair and converted into the electrical signal (direct piezoelectric effect) transmitted to BOI for processing. The control electrical signal is sent alternately to each of the transceivers.
Features of measuring gas or fluid medium flow speed and flow rate
There are several ways to measure using ultrasonic waves:
1. Direct measurement.
2. Measurement with re-reflection.
Direct measurement supposes that the sensors are oriented towards each other and perform direct measurement.
The re-reflection measurement supposes that the sensors use special sites so that the acoustic wave, reflecting from it, is directed to the response sensor. There may be several such sites.
Each of the above measurement methods is based on calculation of time difference while ultrasonic beam passing in the flow and against the flow. The higher the time difference, the higher the flow speed, and therefore the flow rate. All the calculations are performed using microprocessors and the algorithms built in the computer.
Depending on the model, ultrasonic flow meters differ in functionality and engineering factors: limits and measurement accuracy. For devices of different classes, restrictions are imposed on the operating range of temperatures and pressures.
