Basic of Portable Ultrasonic Flow Meters
Time:2022-11-14 Read:278
Reading guide: The installation process is extremely simple, and the human-computer interface can be switched between Chinese and English, making it easier to operate. Especially suitable for flow balance test and flow monitoring: drinking water, river water, seawater, cooling water, hot water, industrial sewage, lubricating oil, diesel oil, fuel chemical liquid, etc.

Product characteristics

1. Non-contact measuring mode, small in size, lightweight, clamp-on type ultrasonic flow meter, and easy to carry.
2. The installation of the sensor is simple and easy, and it is used to measure the acoustic medium of various sizes of pipes.
3. The measurement process does not need to damage the pipeline and stop production. The sensor does not contact with the measured medium and has no pressure loss.
4. Suitable for measuring metal pipes, plastic pipes, and other sound transmission materials.
5. The built-in rechargeable battery can work continuously for more than 12 hours.
6. Intelligent on-site printing function ensures the integrity of flow data.

Brief description

The portable ultrasonic flow meter uses the principle of low voltage and multi-pulse time difference and adopts high-precision and ultra-stable double-balanced signal differential transmission and differential reception digital detection technology. When the ultrasonic beam propagates in the liquid, the liquid flow will cause a small change in the transmission time, which is proportional to the liquid flow rate. When the flow is zero, the time required for the two sensors to transmit and receive sound waves is exactly the same (the only technology that can actually measure the zero flow). When the liquid flows, the sound wave transmission time in the countercurrent direction is greater than that in the downstream direction. The relationship conforms to the following expression:

The three unique installation methods of portable ultrasonic flow meter make the measurement and installation simple, convenient, and flexible. Online measurement and calibration patrol measurement have been widely used in petroleum, chemical, metallurgy, light textile, environmental protection, food and other departments, water conservancy construction, and other fields.

Portable Ultrasonic Flow Meter manufacturers

Basic principles

Basic principle and type of ultrasonic flow meter Ultrasonic waves carry the information of fluid velocity when it propagates in flowing fluid. Therefore, the flow velocity of the fluid can be detected through the received ultrasonic wave, which can be converted into the flow rate. The detection method can be divided into different types of ultrasonic flow meters, such as propagation velocity difference method, Doppler method, beam offset method, noise method, and correlation method. The acoustic flow meter is a kind of flow meter that has been applied with the rapid development of integrated circuit technology in recent ten years.

The non-contact instrument is suitable for measuring the fluid that is not easy to contact and observe and the flow rate of large pipe diameter. It is linked with the water level gauge to measure the flow of open water flow. The use of ultrasonic flow ratio does not require the installation of measuring elements in the fluid, so it will not change the flow state of the fluid and generate additional resistance. The installation and maintenance of the instrument will not affect the operation of the production pipeline, so it is an ideal energy-saving flow meter.

As we all know, the current industrial flow measurement generally has problems with large pipe diameters and large flow measurements. This is because the general flow meter will bring difficulties in manufacturing and transportation with the increase in measuring pipe diameter. The cost increase, energy loss increase, and installation are not only these shortcomings but also the ultrasonic flow meter can be avoided. Because all kinds of ultrasonic flow meters can be installed outside the pipe for non-contact flow measurement, the cost of the instrument is basically independent of the diameter of the pipe being measured, while the cost of other types of flow meters increases significantly with the increase of the diameter, so the larger the diameter, the better the function price ratio of the ultrasonic flow meter is compared with other types of flow meters with the same function. It is considered to be a good instrument for measuring the flow of large pipe diameters. 

The Doppler ultrasonic flow meter can measure the flow of a two-phase medium, so it can be used for the measurement of sewage, sewage, and other dirty flows. In power plants, it is much more convenient to use a portable ultrasonic flow meter to measure the water inflow of hydraulic turbines, circulating water volume of steam turbines, and other large pipe diameters than the pitot tube flow meter in the past. Ultrasonic flow measurement can also be used for gas measurement. The pipe diameter is applicable from 2cm to 5m, from open channels and closed channels with a width of several meters to rivers with a width of 500m.

In addition, the flow measurement accuracy of ultrasonic measuring instruments is almost not affected by the temperature, pressure, viscosity, density, and other parameters of the measured fluid, and they can also be made into non-contact and portable measuring instruments, which can solve the flow measurement problems of highly corrosive, non-conductive, radioactive, flammable and explosive media that are difficult to be measured by other types of instruments. In addition, in view of the characteristics of non-contact measurement and reasonable electronic circuits, one instrument can be used to measure a variety of pipe diameters and flow ranges. 

The adaptability of the ultrasonic flow meter is incomparable to other instruments. The clamp-on ultrasonic flow meter has the above advantages, so it has been paid more and more attention and developed towards product serialization and generalization. It has been made into standard type, high-temperature type, explosion-proof type and wet type instruments with different sound channels to adapt to flow measurement of different media, different occasions, and different pipeline conditions.

Portable Ultrasonic Flow Meter factory

At present, the shortcomings of the ultrasonic flow meter are that the temperature range of the measurable fluid is limited by the temperature resistance of the ultrasonic energy transfer aluminum and the coupling material between the transducer and the pipe, and the original data of the measured fluid sound transmission velocity under high temperature is incomplete. At present, it can only be used to measure fluids below 200 ℃ in China. In addition, the measuring circuit of the ultrasonic flow meter is more complex than that of the general flow meter. This is because the flow rate of liquid in general industrial measurement is usually several meters per second, while the propagation speed of the sound wave in liquid is about 1500 m/s, and the maximum change of sound speed caused by the change of flow rate (flow rate) of the measured fluid is also 10-3 orders of magnitude. If the accuracy of measuring flow rate is required to be 1%, the accuracy of measuring sound speed needs to be 10-5~10-6 orders of magnitude, so there must be a perfect measuring line to achieve this, This is the reason why an ultrasonic flow meter can only be applied in practice under the rapid development of integrated circuit technology.

The clamp-on ultrasonic flow meter consists of the ultrasonic transducer, electronic circuit, and flow display and accumulation system. The clamp-on ultrasonic transmitting transducer converts electric energy into ultrasonic energy and transmits it to the measured fluid. The ultrasonic signal received by the receiver is amplified by the electronic circuit and converted into an electrical signal representing the flow for display and totalizer for display and totalization. In this way, the flow detection and display are realized.

The piezoelectric transducer is commonly used in ultrasonic flow meters. It makes use of the piezoelectric effect of piezoelectric materials and uses an appropriate transmitting circuit to add electrical energy to the piezoelectric element of the transmitting transducer to generate ultrasonic vibration. The ultrasonic wave is injected into the fluid at a certain angle and propagates. Then it is received by the receiving transducer and turned into electric energy through the piezoelectric element for testing. The transmitting transducer uses the converse piezoelectric effect of piezoelectric elements, while the receiving transducer uses the piezoelectric effect.

The piezoelectric element of the transducer of the ultrasonic flow meter is usually made into a circular sheet and vibrates along the thickness. The diameter of the sheet is more than 10 times the thickness to ensure the directivity of the vibration. Lead zirconate titanate is mostly used as piezoelectric element material. In order to fix the piezoelectric element, so that the ultrasonic wave can be injected into the fluid at an appropriate angle, it is necessary to put the element into the sound wedge to form a whole transducer (also called the probe). The material of the sound wedge requires not only high strength and aging resistance but also small energy loss after ultrasonic passing through the sound wedge, that is, the transmission coefficient is close to 1. The commonly used sound wedge material is plexiglass, because it is transparent, the assembly of piezoelectric components of the sound wedge can be observed. In addition, some rubber, plastic, and bakelite can also be used as sound wedge materials.

The electronic circuits of an ultrasonic flow meter include transmitting, receiving, signal processing, and displaying circuits. The measured instantaneous flow and cumulative flow values are displayed with digital or analog quantities.

According to the principle of signal detection, the current ultrasonic flow meter can be roughly divided into the propagation velocity difference method (including direct time difference method, time difference method, phase difference method, frequency difference method), beam offset method, Doppler method, correlation method, spatial filtering method, noise method, etc., as shown in the figure. Among them, the noise method has the simplest principle and structure, is easy to measure and carry, is cheap but low in accuracy, and is suitable for use in situations where the accuracy of flow measurement is not required. 

Because the basic principles of the direct TDOA method, TDOA method, frequency difference method, and phase difference method reflect the flow velocity of fluid by measuring the difference between the forward and reverse flow transmission velocities of the ultrasonic pulse, they are also called the propagation velocity difference method. Among them, the frequency difference method and time difference method are widely used because they overcome the error caused by the change of sound speed with fluid temperature and have high accuracy. According to the different configuration methods of transducers, the propagation velocity difference can be divided into the Z method (transmission method), V method (reflection method), X method (cross method), etc. 

The beam migration method reflects the fluid velocity by using the deviation of the propagation direction of the ultrasonic beam in the fluid with the change of the fluid velocity. At low velocity, the sensitivity is very low and the applicability is not great. Doppler method is to use the acoustic Doppler principle to measure the ultrasonic Doppler scattering of scatterers in uneven fluid.

Portable (clamp-on) Ultrasonic Flow Meter suppliers

It is applicable to the measurement of fluid flow containing suspended particles, bubbles, etc. The correlation method to measure the flow by using correlation technology. In principle, the measurement accuracy of this method is independent of the sound velocity in the fluid and therefore is independent of the fluid temperature, concentration, etc., so the measurement accuracy is high and the application scope is wide. However, the correlator is expensive and the circuit is complex. This shortcoming can be overcome after the popularization and application of microprocessors. The noise method (audiometric method) is based on the principle that the noise generated when the fluid flows in the pipeline is related to the flow rate of the fluid. The flow rate or flow value is expressed by detecting the noise. The method is simple and the equipment is cheap, but the accuracy is low.

The above methods have their own characteristics and should be selected according to the properties of the measured fluid, velocity distribution, pipeline installation location, requirements for measurement accuracy, and other factors. Generally speaking, the frequency difference method and time difference method are often used because the temperature of the working medium cannot be kept constant in industrial production. The direct TDOA method is only used when the pipe diameter is large. 

The principle for selecting the installation method of the transducer is generally: when the fluid flows parallel to the pipe axis, the Z method is selected; When the flow direction is not parallel to the tube uranium or the installation location of the pipeline restricts the installation interval of the transducer, V method or X method shall be adopted. When the flow field distribution is uneven and the straight pipe section in front of the surface is short, multi-channel (such as dual channel or four channel) can also be used to overcome the flow measurement error caused by the velocity disturbance. 

The Doppler method is suitable for measuring two-phase flow, which can avoid the problems of blockage, abrasion, adhesion, and non-operation caused by suspended particles or bubbles in conventional instruments, so it has been developed rapidly. With the development of industry and the development of energy conservation, the transportation and application of coal oil mixture (COM), coal cement mixture (CWM) fuel, and the development of energy conservation methods such as fuel oil adding water to support combustion, all open up broad prospects for the application of Doppler ultrasonic flow meter.

Application Guide

It has unique applications in the petrochemical industry, nuclear power industry, and heat transfer oil field, and uses the energy calculation function, which can introduce temperature signals while measuring flow to obtain energy parameters.