Flow instrument is also called flowmeter. The common flowmeter always are: 1. Vortex flowmeter; 2. Electromagnetic flowmeter; 3. float flowmeter; 4. Coriolis force mass flowmeter; 5. Heat type (gas) mass flowmeter; 6. ultrasonic flowmeter; 7. vortex flowmeter
The development of flow measurement can be traced back to ancient hydraulic engineering and urban water supply system. Ancient Roman caesars have used orifice to measure the amount of drinking water. Weirs were used to measure the Nile's flow in ancient Egypt around 1000 BC. The famous dujiangyan water conservancy project in China USES the water level at the mouth of the bottle to observe the water level and so on. In the 17th century, torricelli laid the theoretical foundation of differential pressure flowmeter, which was a milestone in flow measurement. Since then, many types of flow measurement in the 18th and 19th century instrument prototype began to form, such as weir, tracer method, pitot tube, venturi tube, volume, quality, turbine and target flowmeter, etc. Due to the process industry in the 20th century urban public utilities, energy metering, rapidly growing demand for flow measurement, has rapid development, the rapid development of microelectronics technology and computer technology greatly promote upgrading, new type of flowmeter have sprung up. So far, hundreds of flowmeters are said to be on the market, and many of the toughest problems in field use are expected to be solved.
China's modern flow measurement technology is relatively late in the work, the early flow meters are imported from abroad.
Flow measurement is the study of material quantity, quality mutual change rule is the basic rule of things, so the measured object is not limited to the traditional sense of the pipeline fluid, where to master the quantity has the problem of flow measurement. The flow rate, pressure and temperature are listed as three parameters. For a given fluid, its energy can be calculated by knowing these three parameters, which must be detected in the measurement of energy conversion. Energy conversion is the basis of all production processes and scientific experiments, so flow is the most widely used as well as pressure and temperature instruments. ,
1. Electromagnetic flowmeter is a new type of flow meter developed rapidly with the development of electronic technology in the 1960s. It is made from Faraday's law of electromagnetic induction and is used to measure the volume flow of conductive fluid. Due to its unique advantages, it has been widely used in industrial measurement of various conductive liquids.
3. Various inflammable and explosive media; All kinds of industrial sewage, pulp, mud and so on.
2. The thermal type gas mass flowmeter on the principle of thermal diffusion, thermal diffusion technology is a critical technology under the condition of good performance, high reliability, the typical sensors include two thermal resistance (platinum RTD), one is the speed sensor, a temperature sensor is automatically compensate gas temperature changes. When the two RTD are placed in the medium, the speed sensor is heated to a constant temperature difference above the ambient temperature, and the other temperature sensor is used to sense the temperature of the medium. The gas mass flow through the velocity sensor is calculated by the heat transfer of the sensing element. As the gas rate increases, the heat transferred by the sensor to the medium increases, so more power needs to be provided, and the power of the electronic unit heating RTD is related to the mass flow to a certain extent.
Thermal type gas mass flowmeter is new instrument in gas flow measurement, different from other don't need to correct the pressure and temperature, gas flowmeter, direct measurement of gas mass flow rate, a sensor can range from low to high range. It is suitable for the measurement of a single gas and a fixed proportion of multi-component gases. It is based on the principle that the rate at which heat is absorbed by the fluid is directly related to mass flow. Mobile gas molecules absorb heat can be taken away when the impact resistance, flow rate, the greater the thermal contact resistance of molecules, the more the more absorption of heat, heat absorption and a certain the number of molecules of the gas, thermal properties and flow characteristics are concerned.
3. The ultrasonic flowmeter carries the flow rate information when it travels in the flowing fluid. Therefore, the velocity of the fluid can be detected by receiving ultrasonic waves, which can be converted into flow rate. According to the detection method, it can be divided into transmission velocity difference method, doppler method, beam offset method, noise method and correlation method. Acoustic flowmeter is a kind of integrated circuit technology developed rapidly in recent ten years.
4. Turbine flowmeter is a speed meter, which has low pressure loss, high accuracy, low initial flow rate, good seismic and anti-pulsation fluidity, and wide measuring range. Easy maintenance etc, turbine flowmeter is put the turbine flow in the body, when the fluid flow into the timing, in under the action of the special structure of the rectifier rectifier and accelerate, within a certain range of traffic is directly proportional to the angular velocity and flow rate of the turbine, the principle of electromagnetic induction sensor is used to derive and fluid volume flow rate is proportional to the pulse signal, the signal after the preamplifier, plastic, after get the actual flow, and displayed in the LCD screen. If the same temperature, the pressure sensor detects the signal with the input processing of intelligent flow totalizer.especially will receive a standard condition of traffic, and display on the LCD screen.
5. Vortex street flowmeter is a volumetric flowmeter for measuring volume flow of gas, steam or liquid, volume flow rate of standard condition or mass flow produced according to Karman's principle of vortex street. It is mainly used for flow measurement of medium fluids in industrial pipelines, such as gas, liquid and steam.
It is characterized by small pressure loss, large range of measuring range and high precision. It is almost independent of fluid density, pressure, temperature, viscosity and other parameters when measuring volume flow under working conditions. No moving mechanical parts, so high reliability, small maintenance. Instrument parameters can be stable for a long time. Vortex street flowmeter using piezoelectric stress sensor, high reliability, can be in - 20 ℃ ~ + 250 ℃ temperature range. With analog standard signal and digital pulse signal output, it is easy to be used with computer and other digital systems. It is an advanced and ideal measuring instrument.