In recent years, along with the development of electronic technology, digital technology, using the ultrasonic pulse measurement of fluid flow technology develops very fast, based on different principle, applicable to different situations of various type of ultrasonic flow meter has been widely applied, but also for the vast number of users put forward how to realize flow meter ultrasonic, how to choose the appropriate type,  what problems should be paid attention to in the use of ultrasonic flow meter and a series of problems, this paper synthesizes the current development of domestic ultrasonic flow meter and many years of application practice, the above problems are discussed.

1. Classification of ultrasonic flow meter

There are many kinds of ultrasonic flow meters, according to different classification methods, can be divided into different types of ultrasonic flow meters.

1.1 Doppler ultrasonic flowmeter

Ultrasonic signals with the frequency of F1 are transmitted by transducer 1. After passing through suspended particles or bubbles in the liquid in the pipe, the frequency is offset and reflected to transducer 2 at the frequency of F2. This is the doppler compromise, and the difference between F2 and F1 is the multi-spectral doppler frequency difference fd.

Let the fluid velocity be V, the ultrasonic sound velocity be C, and the doppler frequency shift fd is proportional to the fluid velocity v,  So the flow velocity

When the pipe conditions, transducer installation position, emission frequency and sound velocity are determined, C, F1 and θ are constants, and the fluid velocity is proportional to the doppler frequency shift. The fluid velocity can be obtained by measuring the frequency shift, and then the fluid flow can be obtained.

1.2 Time difference type ultrasonic flow meter

The time difference ultrasonic flow meter is used to measure the flow of fluid by using the principle that the time difference between the downstream and counter current propagation of sound waves in the fluid is proportional to the flow rate of fluid.

transducer 1 transmits ultrasonic signals to transducer 2 in the downstream direction, and the propagation time is

On the contrary, the propagation time in the counter current direction is:

The time difference is:

C >> V

So, the flow velocity

Similarly, c, L and θ are constant, and the time difference △t can be used to calculate the flow velocity v and then the flow rate.

2.1 The main differences between the two types of ultrasonic flow meters

(1) Applicable to different occasions

The clamp on ultrasonic flow meter is installed in a fixed position to measure the flow of the fluid in a specific pipe for a long time without interruption. Portable ultrasonic flow meter has great mobility, mainly used for temporary measurement of fluid flow in different pipelines.

(2) Different power supply modes

Fixed ultrasonic flow meters require long - term continuous operation.