Introduction of Rota Meters

In a vertical tapered tube expanded from bottom to top, the gravity of the float with a circular cross-section is borne by the hydrodynamic force, and the float can rise and fall freely in the tapered tube. Under the action of velocity and buoyancy, it moves up and down, balances with the weight of the float, and transmits to the dial through magnetic coupling to indicate the flow. It is generally divided into glass and metal rota meters. Metal rota meters are the most commonly used in industry. Glass is usually used for corrosive media with small pipe diameters. Due to the fragility of the glass itself, rota meters made of precious metals such as titanium are also used for key control points.

The rota meter is a variable area flowmeter based on the position measurement of the float It adopts all metal structures and Modular concept design, with small pressure loss, large range ratio (10:1), convenient installation and maintenance, and can be widely used for flow measurement and process control in complex, harsh environment and various media conditions.

Features

The rotor flowmeter is the most commonly used flowmeter in industry and laboratory. The utility model has the advantages of simple structure, direct viewing, small pressure loss, convenient maintenance, etc. The rotameter is suitable for measuring small flow through pipes with diameters D<150mm, and also for measuring the flow of corrosive media. When in use, the flowmeter is generally installed on the vertical pipe section, and the fluid medium passes through the rotameter from bottom to top. The specially designed rotameter can be installed horizontally or vertically from top to bottom.

Working principle

The rota meter is composed of two parts. One of the rota meters is a tapered tube that expands gradually from bottom to top; The other part of the rota meter is a rotor that is placed in a tapered tube and can move freely down and down the centerline of the tube. When measuring the flow of fluid, the measured fluid flows into the rotor from the lower end of the conical tube, and the fluid flow impacts the rotor and produces a force (the force varies with the flow). When the flow is large enough, the force generated will lift the rotor and make it rise. 

At the same time, when the measured fluid flows through the annular section between the rotor and the tapered pipe wall, there are three forces acting on the rotor: the dynamic pressure of the fluid on the rotor, the buoyancy of the rotor in the fluid, and the gravity of the rotor itself. When the flowmeter is installed vertically, the center of gravity of the rotor will coincide with the axis of the cone tube, and the three forces acting on the rotor will be parallel to the axis of the tube. When the three forces are balanced, the rotor will float stably on a certain position in the tapered tube. For a given rota meter, the size and shape of the rotor have been determined, so its buoyancy in the fluid and its own gravity is known to be constant. Only the dynamic pressure of the fluid on the float changes with the flow velocity of the incoming flow. 

Therefore, when the incoming flow velocity becomes larger or smaller, the rotor will move up or down, and the flow sectional area at the corresponding position will also change until the flow velocity becomes the corresponding speed at equilibrium, and the rotor will be stable at the new position. For a given rota meter, the position of the rotor in the cone tube is in one-to-one correspondence with the flow rate of the fluid flowing through the cone tube.

In order to prevent the rotor from touching the pipe wall when moving down the centerline of the tapered pipe, two methods are usually adopted: one is to install a guide mandrel in the center of the rotor to keep the rotor moving up and down on the centerline of the tapered pipe; the other is to open a chute at the edge of the rotor disk. When the fluid flows through the rotor from bottom to top, it bypasses the rotor while passing through the chute to generate a reverse thrust, Keep the rotor rotating around the centerline, so that the rotor will not touch the pipe wall during operation. The rotor material of the rota meter can be made of stainless steel, aluminum, bronze, etc.

Technical advantages

Relying on the advantages of small pressure loss and large detection range, it has become a very common flow-measuring instrument in industrial control. It is not only convenient to use but also has strong compatibility. It is especially suitable for medium flow measurements with low flow rates and small flow rates. The rota meter has a local display type and intelligent remote transmission type, with pointer display, instantaneous flow, cumulative flow, LCD display, upper and lower limit alarm output, cumulative pulse output, standard two-wire 4-20mA current output, and other forms, providing users with a very broad choice space. In addition, the instrument adopts a high-quality MCU microprocessor system to ensure the excellent performance of the rota meter in various applications.

Over the years, the excellent performance, reliability, and good performance-price ratio of rota meters have been widely favored by the petrochemical, steel, electric power, metallurgy, light industry, and other industries.

1. Suitable for small pipe diameter and low flow rate.
2. Reliable operation, small maintenance, and long service life.
3. Low requirements for the downstream straight pipe section.
4. Wide flow range 10:1.
5. Local pointer indication is close to linearity.
6. The intelligent indicator is equipped with an LCD display, which can display instantaneous and cumulative flow, and output pulses and alarms.
7. With temperature compensation
8. There are local types, remote types, jacket types, horizontal types, explosion-proof types, anti-corrosion types, etc.

Structure

Metal tube float flowmeter mainly consists of three parts
A. Indicator (intelligent indicator, local indicator)
b. Float
c. Conical measuring chamber

Measurement method

Connect the transparent water pipe, use the water column to raise the setting pressure, use a high-sensitivity digital multimeter to measure the voltage, and connect the sensor with 12v voltage. Record data. If the relationship is linear, it indicates that the performance is stable and can be used. The differential pressure sensor is connected to two pressure pipes through the air pipe. When liquid flows through the liquid guide pipe, the pressure difference between the input pipe and the output pipe will be generated. The pressure of the input pipe is greater than the pressure of the output pipe. The differential pressure sensor detects this pressure difference and converts it into a voltage signal.

The fault debugging of the rotameter during the debugging period expects that the fault will generally occur in the instrument installation and debugging stage. Once it is eliminated, it will not occur again under the same conditions in the future. Common faults during the commissioning period are generally caused by improper installation, environmental interference, and fluid characteristics. The output signal will also fluctuate to some extent. When two or more liquids are used in the pipeline mixing process, if the conductivity (or potential between them and electrodes) of two liquids are different, they will enter the flow sensor for flow measurement before mixing is uniform, and the output signal will also fluctuate. The sensor can be installed horizontally and vertically, but the influence of sediment and bubbles on the measuring electrode should be avoided. It is better to keep the electrode horizontal in the axial direction. When installed vertically, the fluid should flow from bottom to top. The sensor cannot be installed at the highest position of the pipe, which is easy to accumulate bubbles.

Application introduction

Glass rotameters are widely used in the chemical industry, petroleum, light industry, medicine, environmental protection, food, measurement and testing, scientific research, and other departments to measure the flow of single-phase non-pulsating fluid (liquid or gas).

The glass rotameter has strong corrosion resistance and can detect the flow of acid (except hydrofluoric acid), alkali, oxidant, and other corrosive gases or liquids. It is suitable for chemical, pharmaceutical, paper making, sewage treatment, and other industries.

The Development of Rota Meters

The development of flow measurement can be traced back to ancient water conservancy projects and urban water supply systems. Orifice plates were used to measure the amount of drinking water in ancient Rome during Caesar's time. Around 1000 BC, ancient Egypt used the weir method to measure the flow of the Nile. The famous Dujiangyan Water Conservancy Project in China uses the water level at Baopingkou to observe the water volume and so on. Torricelli laid the theoretical foundation of the differential pressure flowmeter in the 17th century, which is a milestone in flow measurement. Since then, the rudiments of many types of flow measurement instruments in the 18th and 19th centuries began to take shape, such as weir, tracer method, pitot tube, venturi tube, volume, turbine, and target flowmeter. 

In the 20th century, due to the rapid growth of the demand for flow measurement in the process industry, energy metering, and urban utilities, the rapid development of instruments was promoted. The rapid development of microelectronics and computer technology greatly promoted the upgrading of instruments, and new types of flow meters sprang up like mushrooms. Up to now, it is said that hundreds of flowmeters have been put into the market, and many difficult problems in on-site use are expected to be solved.

Flow measurement is a science that studies the change of material quality, and the law of mutual change of mass is the basic law of the development of the relationship between things. Therefore, its measurement object is not limited to the traditional sense of pipeline liquid, and where it is necessary to master the quantitative change, there is a problem with flow measurement. Flow, pressure, and temperature are three major detection parameters. For a given fluid, its energy can be calculated as long as these three parameters are known, and these three parameters must be detected in the measurement of energy conversion. Energy conversion is the basis of all production processes and scientific experiments, so flow, pressure and temperature instruments are the most widely used.