What Is a Rotameter?
The rotor flowmeter measures fluid flow based on the principle of throttling, but it changes the flow area of the fluid to keep the differential pressure above and below the rotor constant, so it is also called a variable flow area constant differential pressure flowmeter, also known as a float flowmeter. [1]
Rotameter
- The rotor flowmeter measures fluid flow based on the principle of throttling, but it changes the flow area of the fluid to keep the differential pressure above and below the rotor constant, so it is also called a variable flow area constant differential pressure flowmeter, also known as a float flowmeter. [1]
- Rotameter is the most commonly used flowmeter in industry and laboratory. It has a simple, intuitive,
- The rotor flowmeter consists of two parts. One of the rotor flowmeter is a conical tube that gradually expands from bottom to top. The other is a rotor that is placed in a conical tube and can move freely along the centerline of the tube. . Rotor flowmeter When measuring the flow of fluid, the measured fluid flows in from the lower end of the conical tube. The flow of the fluid impacts the rotor and generates a force on it (the magnitude of this force varies with the flow); when the flow is large enough At this time, the generated force lifts the rotor and raises it. At the same time, the measured fluid flows through the annular section between the rotor and the conical tube wall. At this time, 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 and the axis of the cone tube coincide, and the three forces acting on the rotor are in a direction parallel to the tube axis. When these three forces reach equilibrium, the rotor floats smoothly at a certain position within the cone. For a given rotor flowmeter, the size and shape of the rotor have been determined, so its buoyancy in the fluid and its own gravity are known to be constant. Only the dynamic pressure of the fluid on the float changes with the flow velocity. . Therefore, when the incoming flow velocity becomes larger or smaller, the rotor will move upwards or downwards, and the flow cross-sectional area at the corresponding position will also change. Until the velocity becomes equal to the corresponding speed, the rotor will be stable at the new position. For a given rotor flowmeter, the position of the rotor in the cone tube corresponds to the flow rate of the fluid flowing through the cone tube.
- In order to prevent the rotor from hitting the wall of the tube when moving on and down the centerline of the conical tube, two methods are usually used: one is to install a guide core rod in the center of the rotor to keep the rotor at the centerline of the conical tube. Up and down movement, the other is a chute on the edge of the rotor disc. When the fluid flows through the rotor from the bottom to the side, it bypasses the rotor at the same time and generates a reverse thrust through the chute, so that the rotor does not move around the centerline. Stopping rotation can keep the rotor from hitting the wall of the pipe during work. Rotor flowmeter rotor material can be made of stainless steel, aluminum, bronze and so on.
- Relying on the advantages of small pressure loss and large detection range, it has become a very commonly used flow measurement instrument in industrial control. It is not only easy to use, but also has strong compatibility and other advantages. It is especially suitable for medium flow measurement with low flow rate and small flow. Rotary flowmeters have on-site display and intelligent remote transmission, with pointer display, instantaneous flow, cumulative flow, liquid crystal display, upper and lower limit alarm output, cumulative pulse output, standard two-wire 4-20mA current output and other forms Provides users with a very wide choice. In addition, the instrument uses a high-quality MCU micro-processing system to ensure the excellent performance of the rotor flowmeter in various applications.
- Over the years, various excellent performances and reliability of rotor flowmeters , as well as better performance-to-price ratio, have been favored by petrochemical, steel, power, metallurgy, light industry and other industries.
- 1.Suitable for small pipe diameter and low flow rate
- 2. Reliable work, low maintenance and long life
- 3. Low requirements for downstream straight pipe sections
- 4.With a wide range of flow 10: 1
- 5. In-place pointer indication is close to linear
- 6. Intelligent indicator with LCD display, can display instantaneous, cumulative flow, can also output pulses, output alarm
- 7.With temperature compensation
- 8. In-situ, remote transmission, jacket type, horizontal type, explosion-proof type, corrosion-resistant type, etc.
- Structure
- Metal tube float flow meter mainly consists of three parts
- a, indicator (intelligent indicator, local indicator)
- b.Float
- c. Conical measurement room
- Connect the transparent water pipe, use the high sitting pressure of the water column, measure the voltage with a high-sensitivity digital multimeter, and connect the sensor with a 12v voltage. Record data. If it has a linear relationship, it means that the performance is stable and can be used. The differential pressure type pressure sensor is connected to two pressure taking pipes through an air pipe. When liquid flows through the catheter, the pressure difference between the input pipe and the output pipe will be generated, and the pressure of the input pipe is greater than the pressure of the output pipe. This pressure difference is detected by a differential pressure sensor and converted into a voltage signal.
- Rotating flowmeters during the commissioning period. The faults are expected to occur during the installation and commissioning of the instrument. Once the faults are eliminated, they will not occur again under the same conditions in the future. Common faults during commissioning are generally caused by improper installation, environmental interference, and the influence of 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 of the two liquids (or the potential between each liquid and the electrode) is different, it will enter the flow sensor for flow measurement before the mixing is not uniform, and the output signal will fluctuate. The sensor can be installed horizontally and vertically, but it should be ensured that the influence of sediment and air bubbles on the measuring electrode is avoided, and the electrode axis should be kept horizontal as well. When installed vertically, the fluid should flow from bottom to top. The sensor cannot be installed in the highest position of the pipeline, this position is prone to air bubbles.
Rotameter Basic
- Glass rotor flowmeters are widely used in chemical, petroleum, light industry, pharmaceutical, environmental protection, food and metrology testing, scientific research and other departments to measure the flow rate of single-phase non-pulsating fluids (liquid or gas).
- The glass rotor flowmeter has strong corrosion resistance and can detect the flow of acids (except hydrofluoric acid), alkali, oxidants and other corrosive gases or liquids. It is suitable for chemical, pharmaceutical, papermaking, sewage treatment and other industries.
Development of Rotameter
- The development of flow measurement can be traced back to ancient water conservancy projects and urban water supply systems. In the Roman caesar era, orifice plates were used to measure the drinking water of residents. Weir method was used in ancient Egypt around 1000 BC to measure the discharge of the Nile. The well-known Dujiangyan water conservancy project in our country uses the water level of the treasure bottle mouth to observe the amount of water and so on. In the 17th century, Torri demolition laid the theoretical foundation for differential pressure flow meters, which is a milestone in flow measurement. Since then, the prototypes of many types of instruments for flow measurement in the 18th and 19th centuries have begun to form, such as weirs, tracers, pitot tubes, venturis, volumes, turbines, and target flow meters. In the 20th century, due to the rapid increase in demand for flow measurement in process industry, energy metering, and urban utilities, the rapid development of meters was promoted. The rapid development of microelectronics and computer technology has greatly promoted the upgrading of meters, and new flowmeters have sprung up like mushrooms. . So far, it is said that hundreds of flowmeters have been put on the market, and many difficult problems in field use are expected to be solved.
- It is relatively late to carry out modern flow measurement technology in China, and the flow meters required in the early days are imported from abroad.
- Flow measurement is a science that studies the change of mass. The law of mass change is the basic law of the development of the relationship between things. Therefore, the measurement object is not limited to the traditional pipeline liquid. There is a problem of flow measurement in all places where the volume change needs to be mastered. Flow rate, pressure and temperature are listed as the three major detection parameters. For a certain fluid, as long as these three parameters are known, the energy can be calculated, 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 and pressure and temperature instruments are the most widely used.
Rotary flowmeter measurement range
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Rotary Flowmeter Installation Note
- In order to allow the rotor flowmeter to work normally and achieve a certain measurement accuracy, pay attention to the following points when installing the flowmeter:
- 1. The rotor flowmeter must be installed vertically on a pipe without vibration. The fluid flows through the flowmeter from bottom to top, and the verticality is better than 2 °, and the horizontal included angle is better than 2 ° when installed horizontally; (there is a rotor flowmeter that can be installed horizontally)
- 2. In order to facilitate the maintenance and replacement of the flowmeter and cleaning of the measurement pipeline, the metal tube float flowmeter installed on the process pipeline should be equipped with a bypass pipeline and a bypass valve;
- 3. At the entrance of the rotor flowmeter, there should be a straight pipe section with a length of more than 5 times the pipe diameter, and at the exit, there should be a straight pipe section of 250mm;
- 4. If the medium contains ferromagnetic substances, a magnetic filter should be installed; if the medium contains solid impurities, consider installing a filter between the valve and the straight pipe section;
- 5. When used for gas measurement, ensure that the pressure of the pipeline is not less than 5 times the pressure loss of the flowmeter to make the float work stably;
- 6. In order to avoid deformation of the flowmeter caused by the pipeline, the flange of the process pipeline must be coaxial with and parallel to the flange of the flowmeter. The pipeline is supported to avoid pipeline vibration and reduce the axial load of the flowmeter. The valve should be installed downstream of the flow meter:
- 7. When measuring gas, if the gas is directly discharged into the atmosphere at the outlet of the flow meter, a valve should be installed at the outlet of the instrument, otherwise the pressure drop at the float will cause data distortion.
- 8. When installing the instrument with PTFE lining, the flange nut should not be tightened randomly and asymmetrically, so as not to cause deformation of the PTFE lining;
- 9. For instruments with liquid crystal display, try to avoid direct sunlight to avoid reducing the service life of the LCD; For instruments with lithium battery, try to avoid direct sunlight and high temperature environment (65 ) to avoid reducing the capacity and life.
Selection of rotor flowmeter
- 1. For the selection of remote transmission type metal tube float rotor flowmeter, choose a rotor flowmeter suitable for the type of explosion-proof requirements of the place of use; during installation, attention should also be paid to the tightening of the housing after the meter is powered on and the sealing of the connection port, which has reached explosion-proof , Protection, anti-erosion requirements.
- 2. For locations where the temperature of the measured medium is too high (> 120 ° C) or too low, it is usually necessary to take thermal or thermal insulation measures on the sensor part of the rotor flowmeter. In order to ensure that the signal converter ------ indicator is normal The working ambient temperature should be a high temperature indicator.
- 3. For some measured mediums that need to be insulated or cooled, jacket-type rotor flowmeters should be selected. The heating or cooling interface of the standard metal tube float rotor flowmeter adopts the DIN2501 DN15 PN1.6 flange connection. If other flanges or screw connections are required, please specify when ordering.
- 4. For the unstable pressure of the inlet medium of the rotor flowmeter, especially for gas measurement, to ensure accuracy and service life, a damping structure should be selected.
- 5. The pressure level required for the medium is higher. When exceeding the standard pressure level, please choose a high-pressure type structure when selecting the type. The high-pressure type uses HG20595-97 RF butt-welded steel pipe flanges. If other standards are used, please specify when ordering.
- 6. When the rotor flowmeter is installed, the verticality of the measuring tube should be better than 5%, and a bypass should be installed to facilitate maintenance and cleaning without affecting production.
- 7. The position of the rotor flow meter should be installed to ensure that the inlet has a straight pipe section 5DN and the outlet is not less than 250 mm. If the medium contains ferromagnetic substances, a magnetic filter should be installed in front of the rotor flow meter.
- 8. The control valve in the measurement and control system should be installed downstream of the rotor flowmeter. When used for gas measurement, the working pressure should be not less than 5 times the pressure loss of the rotor flowmeter to make the rotor flowmeter work stably.
- 9. Before installing the metal tube float rotor flowmeter, the welding slag in the pipeline should be purged; the stop element in the rotor flowmeter should be removed during installation; when used after installation, the control valve should be opened slowly to avoid impact damage to the rotor flow. meter.
Rotary flowmeter troubleshooting
- The rotor flowmeter has the characteristics of simple structure, reliable operation, wide application range, accurate measurement, convenient installation, etc., and has high temperature resistance and high pressure resistance. How to troubleshoot common faults during flowmeter operation?
- I. No current output
- 1. First see if the wiring is correct.
- 2. Whether the LCD has a display, if there is no output, the output tube is mostly broken, and the circuit board needs to be replaced.
- 3. Lost calibration value. Due to the failure of E2PROM, the calibration data of the instrument is lost, and no output current will be caused, and the current will remain unchanged. Solution: The data recovery operation is available. If it does not work, you can set the data in password 2000 first, and then set the data in password 4011. The method is to manually push the pointer to calibrate the data from RP to 100%.
- No on-site display
- 1. Check if the wiring is correct.
- 2. Check whether the power supply is correct.
- 3. Reinstall the LCD module, and check the contact is not correct.
- 4. For multi-wire power supply mode, check whether terminals 12 and 13 are connected to ammeter or short circuit.
- Third, the alarm is incorrect
- 1. Check that the deviation setting d cannot be too large.
- 2. Whether the logic function is correct in the FUN function. HA-A stands for positive upper logic. LA-A stands for lower limit positive logic.
- 3. Check the alarm value setting size in SU.
- 4. If the LCD bar code is correct and the output is inactive, you can check whether the external power source and the negative pole of the external power source are connected to the negative pole of the instrument.
- Fourth, the rotor flowmeter pointer jitter:
- 1. Slight pointer shake: Generally caused by media fluctuations. This can be overcome by increasing damping.
- 2. Moderate pointer jitter: Generally caused by the state of media flow. For gas, it is generally caused by the unstable operating pressure of the medium. Can use voltage stabilization or flow stabilization device to overcome or increase the air flow damping of the float flowmeter.
- 3. Vigorous pointer jitter: Mainly due to the pulsation of the medium, the unstable air pressure, or the pressure, temperature, and flow rate of the gas operating state given by the user do not match the actual state of the float flowmeter, and there are large differences that cause the float flowmeter to overrange.
- Five, the pointer of the float meter stops at a certain position
- The main reason is that the float of the float flowmeter is stuck.
- Generally, because the float flowmeter opens the valve too quickly during use, the float quickly hits the stopper upwards, causing the stopper to deform and the floater stuck. However, it is not ruled out that the float is stuck because the float guide rod and the stop ring are not concentric. When processing, you can remove the instrument, remove the deformed stopper, and check whether it is concentric with the guide rod. If the concentricity can be corrected, then install the float, push the float by hand, and feel that the float is smooth. Yes, in addition, the float flowmeter must be installed vertically or horizontally, and cannot be tilted, otherwise it may easily cause a card meter and bring errors to the measurement.
- Large measurement error of float flowmeter
- 1. Installation does not meet requirements
- For vertical installation of float meter, keep it vertical, and the inclination angle should not be greater than 20 degrees
- For horizontal installation of the float flowmeter, keep it horizontal, and the inclination angle is not greater than 20 degrees
- There should be no ferromagnetic objects in the 100mm space around the float meter.
- The installation position should be far away from the valve reducing port, the pump outlet, and the turning point of the process pipeline. To maintain the requirements of the first 5D after the 250mm straight pipe section.
- 2. Large density change of liquid medium is also a cause of large error. Before the instrument is calibrated, the medium is converted according to the density given by the user, and converted to the water flow under the calibration state for calibration. Therefore, if the medium density changes greatly, it will cause a large error in the measurement. The solution method is to bring the changed medium density into the formula, convert it into an error correction coefficient, and then multiply the flow rate measured by the flow meter by the coefficient to replace the real flow rate.
- 3. Since the gas medium is greatly affected by temperature and pressure, it is recommended to use the temperature and pressure compensation method to obtain the true flow rate.
- 4. Due to long-term use and pipeline vibration and other factors, the floating flowmeter sensing magnetic steel, pointer, counterweight, rotating magnetic steel and other moving parts are loose, causing large errors. Solution: Push the pointer by hand to verify. First press the pointer at the RP position to see if the output is 4mA and whether the flow rate display is 0%, and then verify according to the scale. If a discrepancy is found, the position of the component can be adjusted. Generally requires professional adjustment, otherwise it will cause position loss and need to return to the factory for correction.
- Seven, the cumulative pulse output is incorrect
- 1. Check if the alarm value of the accumulated pulse output is set to zero.
- 2. The circuit board is faulty. Replace the circuit board.
- Eight, the liquid crystal on-site display of the metal rotor flowmeter always displays 0 or full scale
- 1. Check the set range and zero parameters in the 2000 password. ZERO is required to be less than the value of SPAN, and the two values cannot be equal.
- 2. Check if the sampling data comes up, push the pointer with your hand to see the sampling value change. If there is no change, the sampling circuit of the circuit board is generally faulty and the circuit board needs to be replaced.
- 3. The circuit board is faulty. Replace the circuit board.