The ultrasonic flow meter measures the liquid flow rate quickly and effectively. There are two types of ultrasonic flowmeter technology: Doppler frequency shift and transit time.

Transit time ultrasonic flow meter is most suitable for measuring the flow of cleaning liquid. Therefore, it is the most popular type of ultrasonic meter.

Doppler ultrasonic flow meter can measure the frequency difference of sound waves reflected from bubbles or particles in the airflow. It is suitable for aerated or dirty liquids.

Sino-Inst offers a variety of  Ultrasonic flow meters for flow measurement. If you have any questions, please contact our sales engineers.

## Transit time Ultrasonic Flow Meter Working Principle

Transit time Ultrasonic Flow Meter adopts the measurement principle of time difference method. It uses the ultrasonic wave emitted by the sensor to propagate in the flowing fluid. The sound wave propagation speed in the downstream direction will increase, and the backward direction will decrease. In the same propagation distance, there will be different transmission times. According to the difference between the transmission time and the measured The relationship between fluid velocity measures the fluid velocity.

The flow rate of the fluid is different in different positions in the tube. The flow rate in the center of the tube is faster than the flow rate near the wall of the tube. The flow velocity distribution of the fluid in the pipeline can be represented by the flow velocity cross-sectional distribution diagram.

By setting the flowmeter and considering the cross-sectional distribution of the flow velocity, the average flow velocity can be calculated. Then the volume flow of the fluid can be obtained according to the cross-sectional area of the pipe.

Notes:
V measure fluid velocity
M ultrasonic reflection times
D pipe diameter
θ The angle between the ultrasonic signal and the fluid
T up The time when the downstream sensor transmits the signal to the upstream
T down Time from upstream sensor to downstream
ΔT = T up – T down

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## Ultrasonic Doppler Flow Meter Working Principle

Ultrasonic Doppler Flow Meter uses the physical principle of Doppler frequency shift to measure the water flow velocity.

Doppler effect (Doppler frequency shift) principle:
The sound waves emitted by one object are received and reflected by another object. If the object emitting the sound wave is moving relative to the receiving object. The frequency of the sound wave received by the receiving object will be different from the frequency of the emitted sound wave.

If the relative distance between two objects is reduced, the received frequency will increase.
If the relative distance between two objects is increased, the received frequency will decrease.

Such Doppler effects often occur in daily life. For example: when you hear the sirens (sounds) of an oncoming police car. The sound will appear higher in frequency. When the police car is far away from you, the sound it hears will become lower.

Through the difference between the frequency of transmitting ultrasonic waves and the frequency of receiving ultrasonic waves, the specific flow rate can be calculated. Then the water level is measured by the pressure sensor, and the water passing area is calculated from the water level and channel size.
Finally, the velocity and area are integrated to calculate the final instantaneous flow.

Calculation formula:
Velocity × water area × 3600 seconds = instantaneous flow rate (cubic meters/hour)

## Ultrasonic Open channel flow meter working principle

The open channel flowmeter is based on the specific shape of the Parshall metering groove/weir plate metering groove. It guarantees a certain liquid level and knows a certain flow rate. The Parshall groove/weir plate metering groove is selected as the specific flow channel. The measurement accuracy is high. Easy to install.

The sensor measures the height of the liquid level, which is processed by 89C52 series single-chip microcomputers to obtain the instantaneous flow and cumulative flow values.

The flow can be expressed by the following formula:
Q=KHn
Q: Instantaneous flow rate (t/h)

K: Flow rate constant
H: height of liquid level n: nth power value

The instantaneous flow is processed by the cumulative accumulation to obtain the cumulative flow.