The flow sensor is one of the key components in the flow meter, which together with the signal processing component, data transmission and communication component constitutes the flow meter calculation and device. Flow meter plays a very important role in energy measurement, industrial and agricultural production process parameter measurement, environmental protection engineering detection and scientific experiments, and is also one of the main instruments in process automation instruments and devices. Flow sensors include gas sensors, liquid flow and multi-phase flow sensors. The liquid flow sensor includes water flow, oil flow and other liquid flow sensors.
The water flow sensor is a kind of sensor which is used in a large amount and widely used in the flow sensor. It is mainly used for metering, measuring instruments and automatic measurement and control devices such as domestic drinking water, raw water, irrigation water, sewage, urban heating water, domestic hot water, and industrial and agricultural process water in closed pipelines. The measurement of water and heating hot water is the main body. Water flow sensors are known for their rich product categories, numerous varieties and specifications, wide technical coverage, and complicated working environment conditions.
The water flow sensor can be divided into two types of volume sensor and speed sensor according to their different measuring principles. According to the main sensor structure and signal acquisition method, the water flow sensor can be divided into sensors with mechanical motion mechanism (such as: piston type, nutation type, impeller type water flow sensor) and sensors without mechanical motion mechanism (such as: electromagnetic Type, ultrasonic type, jet type water flow sensor) and so on.
Water flow sensors are rarely used alone, and most of them are used in various types of water meters, heat meters, water flow meters and other products, which play a role in sensing and converting the medium flow or flow rate in closed pipes. By processing and displaying its output signal through the signal processing component in the meter, the parameters such as cumulative flow (ie water consumption), instantaneous flow, flow at various periods, and heat can be obtained, and if necessary, the obtained results can be transmitted to the outside world. Communication.
Under normal circumstances, the flowmeters and meters used for water flow measurement and control in industrial and agricultural processes, their sensors usually work in a narrow flow range, and the instantaneous flow rate or flow of water in the pipeline is the main measurement and control target, and the working environment conditions Generally, it is better; the water flow sensors in water meters and heat meters are obviously different. They require the sensors to have a wide flow measurement range to meet the requirements of different water flow measurements in the same pipeline. At the same time, due to the harsh working environment, it cannot be powered by grid power. Therefore, smart electronic water meters and heat meters must be designed with micro-power consumption and battery-powered, and should have the characteristics of reliable work in humid and flooded environments.
Mainstream water flow sensor
The number of water flow sensors for domestic drinking water and heating water accounts for more than 80 of the total. They can represent the basic conditions and characteristics of water flow sensors in many ways. At present, the number of water flow sensors used in various types of water meters (including mechanical water meters and smart electronic water meters) in China is particularly large, with an annual output of about 60 million units, accounting for about 45 of the output, of which more than 22 million units are exported; The annual output of water flow sensors used in heat meters is as much as 3 million units.
In the above-mentioned water flow sensors, the large-diameter type usually has an impeller-type horizontal helical wing type and vertical helical wing type structure as the main body, and the small-diameter type has an impeller-type multi-flow beam rotor type and single-flow beam rotor type structure as the main body. This type of impeller sensor that brings motion mechanism is the mainstream water flow sensor commonly used in water supply and heating pipelines. Others such as volumetric water flow sensors also occupy a small share, and are mainly based on rotating piston structures. They are usually used in situations with good water quality and no impurities in the water.
The impeller-type water flow sensor uses a mechanical transmission shaft that is proportional to the flow rate of the pipeline. The impeller and the impeller box and other rotating mechanisms are simple in structure, low in manufacturing cost, and can work stably for a long time under the condition of less impurities in the water. Because the rotation of the impeller cannot be directly output as an electrical signal, such water flow sensors usually use a mechanical accumulation mechanism to accumulate and display water consumption. If you want to directly convert the rotation amount of the impeller, piston, etc. into an electrical signal, you must set up an electromechanical conversion component in the sensor to convert the non-electricity rotation amount into a pulse output incremental coded electrical signal or a positional output coded electrical signal. Facilitate subsequent signal processing and data transmission and communication.
The pulse code signal output needs to use a variety of sensitive components and detection methods. Commonly used are magneto-sensitive detection, eddy current detection and switch detection. The position-coded signal is usually collected by photoelectric direct reading.
The impeller-type water flow sensor can work in a wide measurement range. Because the instrument constant cannot maintain good linearity, the measurement range of this type of sensor will be restricted by the nonlinear characteristics. At present, the computational fluid dynamic CFD method has been used to simulate the flow field of the impeller-type water flow sensor and optimize the flow characteristics.
New water flow sensor
Impeller or piston-type water flow sensor has mechanical movement mechanism, so the shaft system is easy to wear when working, the measurement repeatability is poor, the pressure loss of the pipeline is too large, and the electrical signal needs to be output through the electromechanical conversion component. From a development perspective, The water flow sensor with mechanical movement mechanism will gradually withdraw from the stage of history.
New water flow sensors, such as electromagnetic, ultrasonic, jet and other water flow sensors, because there are no mechanical moving parts in the sensor, they have a long service life, reliable measurement, and low requirements for water quality. The measurement characteristics can be measured by a built-in embedded computer Adjustment and correction are the future sensors of intelligent electronic water meters, heat meters and measuring meters.
The electromagnetic water flow sensor uses the principle of electromagnetic induction to work. The electrical signal output by the sensor is directly proportional to the average flow velocity of the measured water fluid in the pipeline. Electromagnetic water flow sensor has the characteristics of good linearity and repeatability, has nothing to do with the physical property parameter value of the measured medium, and has small pressure loss. It is a sensor with very good performance.
Ultrasonic water flow sensors usually use the propagation time difference measurement method. The velocity or flow rate in the pipeline is proportional to the propagation time and time difference of the ultrasonic waves. Ultrasonic water flow sensor is also a kind of sensor with excellent performance and no mechanical movement mechanism. It also has the characteristics of low pressure loss, good measurement repeatability, wide measurement range, simple sensor structure and so on.
The jet water flow sensor is a fluid oscillation type sensor, which usually uses the jet wall effect and feedback control principle to work. Within a certain flow range, the velocity of the aggregate fluid in the pipeline is proportional to the frequency of jet oscillation. The characteristics of the jet water flow sensor are good, the use is reliable, the working life is long, and the anti-interference ability is strong. However, the upper measurement limit of this sensor is limited by the increase in pressure loss, and the lower measurement limit is limited by the increase in fluid viscosity, which is not easy to oscillate. Therefore, compared with the above two sensors, the measurement range and pressure loss index of the jet water flow sensor are at a disadvantage.
Development trend of water flow sensor
At present, the measurement and measurement of water used for trade settlement and water consumption management in closed pipelines are mainly realized by various types of water meters. Among them, the water flow sensor is dominated by the impeller sensor of the mechanical motion mechanism. With the increasing shortage of fresh water resources, water conservation and scientific water use have been mentioned in very important positions, so the role of water flow meters has become more prominent. How to improve the measurement accuracy of water flow, expand the flow measurement range, improve the measurement reliability and service life, and increase the use of water flow meters (such as: data transmission and communication, intelligent valve control, network access and other functions) Issues to be faced urgently.
From the perspective of market application, in addition to drinking water metering, the demand for agricultural irrigation metering, sewage metering, domestic hot water metering, heating hot water metering, firefighting water metering, etc. is also expanding. Usually, the water quality of these measured media is not good, often with magazines and dirt, and the water flow sensor using a mechanical motion mechanism cannot meet the needs of reliable and continuous measurement. Therefore, it is necessary to use flow meters composed of sensors without mechanical motion mechanisms, such as electromagnetic, ultrasonic, jet and other water flow measuring instruments.
At present, more and more intelligent electronic water meters without mechanical motion mechanisms have entered the market. In advanced developed countries, small-diameter electromagnetic water meters and ultrasonic water meters with wide range, high accuracy, long service life, and communication interface have been initially promoted and applied. Large-diameter electromagnetic water meters and ultrasonic water meters are used in drinking water, sewage, and irrigation. Water metering and industrial and agricultural process measurement have also entered the stage of full application; in China, many companies have shifted the focus of water flow meter research and development to intelligent electronic water meters without mechanical motion mechanisms, and have adopted large-diameter pipe networks. It has been applied to a certain extent.
From the perspective of the application of new technology for water flow sensors, flow sensing and signal processing technology, micro-power design technology, etc. have been widely valued and applied, for the improvement of flow sensor measurement accuracy, measurement range expansion, measurement reliability and The service life guarantee has made an important contribution. In order to enable the original "fragile" electronic instruments to work in harsh environments, the sealing technology, weather resistance, electromagnetic, mechanical environment change technology, reliability design and test technology have also received due attention and research. Because the embedded electronic computer system is built in the intelligent electronic water meter, it can carry out automatic correction, automatic zero setting, automatic compensation, etc. on the sensor characteristics, so that the water flow sensor can better meet the measurement needs. With the large-scale application of Internet of Things and information technology, water flow sensors or meters are also required to have network access and measurable and controllable functions to meet the needs of several monitoring and automatic scheduling of water flow parameters of underground pipeline networks.
From the perspective of the development trend of technical standards, due to increased demand, the measurement accuracy of water flow sensors must be improved, the measurement range must be widened, the repeatability of the measurement must be guaranteed, and the anti-interference characteristics must be strengthened. The new ISO4064 / R49 international water meter standard improves the measurement accuracy of closed-pipe drinking water meters from the original level 2 (large allowable error of ± 2, ± 5) to level 1 (large allowable error of ± 1, ± 3) and Two levels of level 2; the measurement range is improved from the original R = 10 ~ 800 to R = 80 ~ 1000; the measurement repeatability requirements (less than 1/3 of the large allowable error value) are proposed; the electromagnetic environment and climate are strengthened Test requirements for environment, mechanical environment, etc.
Challenges and changes in water flow sensors
The water flow sensor is an important member of the liquid sensor, and the water metering work for trade settlement and water management is the main application field of the water flow sensor. Water flow sensors composed of traditional mechanical motion mechanisms and various types of water meters, heat meters and other meters composed of them are currently used in huge amounts and are in a leading application position. With the continuous expansion of the application range, the requirements for the adaptability and use characteristics of water flow sensors and even instruments are continuously improved, a large number of new technologies have emerged, and the increasing needs of users have brought new challenges and changes to traditional water flow sensors. Claim. The new water flow sensor is the focus of future research and an important direction of development due to its excellent use characteristics and reliability, as well as the diversity of functions. It is worth your efforts and expectations.
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