Ultrasonic flowmeter selection

Ultrasonic flowmeter principle:

According to the principle of signal detection, ultrasonic flowmeters can be divided into propagation velocity difference method (direct time difference method, time difference method, phase difference method and frequency difference method), beam migration method, Doppler method, cross-correlation method, space filter method and noise method.

1, the time difference method: measure the time difference caused by different propagation speeds in the forward and backward propagation to calculate the velocity of the measured flow body.

It uses two acoustic transmitters (SA and SB) and two acoustic receivers (RA and RB). Two sets of sound waves from the same sound source are transmitted between SA and RA and between SB and RB. They are at a θ Angle to the pipe (generally θ=45°) along the position where the pipe is installed. Since sound waves traveling downstream are accelerated by the fluid, and sound waves traveling upstream are delayed, the time difference between them is proportional to the flow rate. The flow rate can also be measured by sending a sinusoidal signal to measure the phase shift between two sets of sound waves or by sending a frequency signal to measure the frequency difference.

2. Phase difference method: Measure the calculation speed of phase difference caused by time difference when propagating forward and backward.

Its transmitter sends a sound wave along an axis perpendicular to the pipe, and the sound beam is shifted some distance downstream due to the fluid flow. The deviation distance is proportional to the flow rate.

3, Frequency difference method: measure the sound ring frequency difference when propagating forward and backward propagation. When ultrasonic waves are transmitted in an inhomogeneous fluid, the sound waves are scattered. When there is relative motion between the fluid and the transmitter, there is a Doppler shift between the transmitted acoustic signal and the signal received after being scattered by the fluid. The Doppler shift is proportional to the fluid velocity.

Ultrasonic flowmeter structure:

Ultrasonic flowmeter is mainly composed of ultrasonic generator, ultrasonic receiver, electronic circuit, flow display, accumulation system. Among them, the ultrasonic generator is mainly used to generate ultrasonic waves and emit them into the fluid; The ultrasonic receiver is mainly used to receive ultrasonic waves after passing through the fluid; After the ultrasonic wave is received, the flow is transmitted to the display screen in the form of an electrical signal after being amplified and converted by the electronic circuit. The cumulative system completes the cumulative calculation of traffic.

Flowmeter selection in different situations:

1, Sewage, pulp and other turbidized liquid media, the choice of flowmeter varieties are: ultrasonic flowmeter and intelligent electromagnetic flowmeter, but in the selection of flow timing to consider the liquid does not contain more air or bubbles.

2, Oil, diesel and other oil media, the optional flowmeter variety is: ultrasonic flowmeter.

3, Mortar, electric slurry and other large concentration, solid particle content of the medium, the optional flowmeter variety is: electromagnetic flowmeter.

4, Tap water large flow medium, the choice of flowmeter variety is: suitable for intelligent electromagnetic flowmeter, ultrasonic flowmeter. Other flowmeters such as vortex flowmeters, orifice flowmeters can also be used.

5, Gas medium, optional flowmeter varieties are: 1, ultrasonic gas flowmeter. 2, vortex flowmeter. If the gas temperature exceeds 300℃, the pneumatic flowmeter is optional.

6, Pure water, salt water and other low conductivity medium, the choice of flowmeter variety is: ultrasonic flowmeter is very suitable for measuring this type of fluid.

7, Acid, alkali and other corrosive media, the choice of flowmeter variety is: 1, acid and alkali resistance lining electromagnetic flowmeter. 2, external clamp type ultrasonic flowmeter.