Ultrasonic flowmeter refers to a flowmeter developed based on the principle that the propagation speed of ultrasonic waves in a flowing medium is equal to the vector sum of the average flow velocity of the measured medium and the speed of sound waves in a stationary medium. It is mainly composed of a transducer and a converter. There are different types such as time difference method, Doppler method, beam shift method, and noise method.

1. Working principle

1. Time difference method (mainstream technology)

Calculate the flow velocity by measuring the time difference between the propagation of ultrasonic waves in the fluid in the downstream and upstream:

2. Doppler method

The flow velocity is calculated by using the frequency shift (Doppler frequency shift) of ultrasonic waves reflected by suspended particles in the fluid. It is suitable for fluids containing particles or bubbles (such as sewage, slurry), but not for pure water.

3. Core advantages

- No flow obstruction: non-contact measurement, no pressure loss, and significant energy saving effect.

- Strong adaptability:

- Wide pipe diameter range (DN15 to DN6000mm), especially suitable for large-diameter pipes;

- Can measure highly corrosive and non-conductive liquids;

- Support high-temperature media (up to 160℃).

- Convenient installation: external clamping type does not require shutdown and has low maintenance costs.

4. Application restrictions

1. Fluid requirements

- The time difference method requires pure fluid (few bubbles and impurities);

- The Doppler method requires the medium to contain sufficient scattering particles.

2. Installation conditions

- Straight pipe section requirements: The time difference method requires 5D before and 3D after (D is the pipe diameter), and the Doppler method requires 10D before and 5D after;

- Full pipe state: When the fluid is not full or contains sediment, the accuracy is affected.

3. Temperature limit: Domestic equipment is usually suitable for ≤200℃ fluid.

Tip: The selection needs to be based on the fluid characteristics, pipe diameter, accuracy requirements and installation conditions. For example, for trade settlement, the time difference method instrument with 0.5 level accuracy is preferred, and the Doppler method is used for sewage measurement.