Describe in detail the advantages and disadvantages of various flow meters

First, the advantages of electromagnetic flowmeter 1. Electromagnetic flowmeter can be used to measure industrial conductive liquid or slurry.

2. No pressure loss.

3. The measuring range is large. The caliber of the electromagnetic flow transmitter is from 2.5mm to 2.6m.

4. The electromagnetic flowmeter measures the volume flow under the working condition of the measured fluid. The measurement principle does not involve the influence of the temperature, pressure, density and viscosity of the fluid.

Disadvantages 1. The application of electromagnetic flowmeter has certain limitations, it can only measure the liquid flow of conductive medium, can not measure the flow of non-conductive medium, such as gas and water treatment better heating water. In addition, its lining needs to be considered under high temperature conditions.

2. The electromagnetic flowmeter determines the volumetric flow under working conditions by measuring the speed of the conductive liquid. According to the measurement requirements, for the liquid medium, the mass flow should be measured. The measurement medium flow should involve the density of the fluid. Different fluid media have different densities and change with temperature. If the electromagnetic flowmeter converter does not consider the fluid density, it is not appropriate to give only the volumetric flow rate at room temperature.

3. The installation and commissioning of electromagnetic flowmeters are more complex than other flowmeters and require stricter requirements. Transmitters and converters must be used together. Two different types of meters cannot be used between them. When installing the transmitter, from the selection of the installation site to the specific installation and commissioning, must strictly follow the product specification requirements. There must be no vibration and no strong magnetic field at the installation site. The transmitter and pipe must have good contact and good grounding during installation. The potential of the transmitter is equal to the fluid being measured. In use, the gas remaining in the measuring tube must be drained, otherwise it will cause a larger measurement error.

4. When the electromagnetic flowmeter is used to measure viscous liquid with dirt, stickies or deposits adhere to the inner wall or electrode of the measuring tube, so that the transmitter output potential changes, brings measurement error, and the dirt on the electrode reaches a certain thickness , may cause the meter to fail to measure.

5. Scale or abrasion of the water supply pipe to change the inner diameter size will affect the original flow value and cause measurement error. For example, if the diameter of a 100mm diameter meter changes by 1mm, it will bring about 2% additional error.

6. The transmitter's measurement signal is a very small millivolt potential signal. In addition to the flow signal, it also contains some signals that are not related to the flow rate, such as phase voltage, quadrature voltage, and common-mode voltage. In order to accurately measure the flow rate, various interference signals must be eliminated to effectively amplify the flow signal. Should improve the performance of the flow converter, it is best to use a microprocessor-type converter, use it to control the excitation voltage, according to the nature of the fluid to be selected excitation method and frequency, you can exclude the in-phase interference and orthogonal interference. However, the improved meter structure is complex and the cost is high.

7. Higher price 2. Advantages of ultrasonic flow meter 1. Ultrasonic flow meter is a non-contact measuring instrument that can be used to measure fluid flow and large tube flow that are difficult to contact and difficult to observe. It does not change the flow state of the fluid, does not generate pressure loss, and is easy to install.

2. The flow of highly corrosive media and non-conductive media can be measured.

3. Ultrasonic flowmeter has a large measuring range, ranging from 20mm to 5m in diameter.

4. Ultrasonic flow meters can measure various liquid and wastewater flows.

5. The volumetric flow rate measured by the ultrasonic flowmeter is not affected by the thermal physical parameters such as temperature, pressure, viscosity, and density of the measured fluid. Can be made in both fixed and portable forms.

Disadvantages 1. Ultrasonic flow meter temperature measurement range is not high, generally only measuring fluid temperature below 200 °C.

2. Poor anti-interference ability. It is susceptible to interference from ultrasonic noises such as air bubbles, scaling, pumps, and other sound sources, affecting the measurement accuracy.

3. Straight pipe sections are strictly required for the first 20D and the last 5D. Otherwise, the dispersion is poor and the measurement accuracy is low.

4. Uncertainty of installation will cause greater errors in flow measurement.

5. The fouling of the measuring pipe will seriously affect the measurement accuracy and bring about significant measurement error. Even when the pipe is serious, the meter will show no flow.

6. Reliability, accuracy level is not high (usually about 1.5 to 2.5), poor repeatability.

7. Short service life (general accuracy can only be guaranteed for one year).

8.Ultrasonic flowmeters determine the volumetric flow rate by measuring the velocity of the fluid. The mass flowrate of the liquid should be measured. The mass flowrate measured by the meter is obtained by multiplying the volumetric flowrate by the artificially set density. When the fluid temperature changes, the fluid Density is variable. Artificially setting the density value does not guarantee the accuracy of the mass flow. The fluid density can only be measured at the same time as the fluid velocity is measured, so that the true mass flow value can be obtained through calculation.

9. The price is higher.

Third, the advantages of vortex flowmeter 1. Vortex flowmeter no moving parts, measuring elements of simple structure, reliable performance, long service life.

2. Vortex flowmeter has a wide measuring range. The range ratio can generally reach 1:10.

3. The volumetric flow rate of a vortex flowmeter is not affected by thermal parameters such as temperature, pressure, density, or viscosity of the fluid being measured. Generally do not need separate calibration. It can measure the flow of liquids, gases or steam.

4. It causes little pressure loss.

5. High accuracy, repeatability 0.5%, and low maintenance.

Disadvantages 1. Volume flow under vortex flowmeter working condition is not affected by thermal parameters such as temperature, pressure, density of measured fluid, but the final measurement result of liquid or steam should be mass flow. For gas, the final measurement result should be Is the standard volume flow. Mass flow or standard volumetric flow must be scaled by fluid density. Fluid density changes due to changes in fluid conditions must be considered.

2. The factors that cause the flow measurement error are: the measurement error caused by the uneven flow velocity of the pipeline; the density of the medium when the fluid working condition changes cannot be accurately determined; and the wet saturated steam is assumed to be dry saturated steam for measurement. If these errors are not limited or eliminated, the total measurement error of vortex flowmeters will be large.

3. Poor vibration resistance. External vibrations can cause vortex flowmeters to produce measurement errors, and may not even function properly. The impact of high flow velocity in the channel fluid will cause additional vibration in the cantilever of the vortex generator body, which will reduce the measurement accuracy. The influence of large diameter is even more pronounced.

4. Poor measurement of dirty media. The body of the vortex flowmeter is easily contaminated by dirt or dirt, changing the size of the geometry and greatly affecting the measurement accuracy.

5. Straight pipe section requirements are high. Experts pointed out that the vortex flowmeter straight pipe section must ensure 20D after the first 40D to meet the measurement requirements.

6. Poor temperature performance. Vortex flowmeters typically measure only fluid flow below 300°C.

IV. Advantages of Orifice Plate Flowmeter 1. The standard throttling piece is universal in the world and has been approved by the international standard organization. It can be used without real flow calibration, and is also the only one in the flowmeter.

2. The structure is easy to copy, simple, firm, stable and reliable performance, low price;

3. Wide range of applications, including all single-phase fluids (liquid, gas, steam), and partially mixed-phase flows. The diameters and working conditions (temperature, pressure) of the general production process are all products.

4. The test piece and differential pressure display instrument can be produced separately from different manufacturers, and it can be produced with professional scale;

Disadvantages 1. The repeatability and accuracy of the measurement are of medium level in the flowmeter. Due to the complexity of the influence of many factors, the accuracy is difficult to improve.

2. The range is narrow. Since the flow coefficient is related to the Reynolds number, the general range is only 3:1 to 4:1.

3. There is a long straight pipe length requirement that is generally difficult to meet. Especially for larger diameters, the problem becomes more pronounced;

4. Large pressure loss;

In order to maintain the normal operation of an orifice meter, the pump requires additional power to overcome the orifice pressure loss. This additional power consumption can be determined directly from pressure loss and flow calculations. It takes about tens of thousands of kilowatt hours a year, equivalent to tens of thousands of yuan. The following table lists the energy consumption calculations for the orifice plate under normal pressure loss conditions. The number of days of operation is calculated on the basis of 350 days, and the price of electricity is calculated on the basis of 0.35 yuan/degree. From the calculation of power consumption data in the table, it can be seen that the additional operating cost of the orifice plate is extremely high, while the operating cost of the elbow flow meter is zero!

5. The hole plate uses the acute angle line of the inner hole to ensure the accuracy. Therefore, it is sensitive to corrosion, wear, scaling, and dirt. It is difficult to ensure the long-term use accuracy. It is necessary to remove the strong inspection once a year.

6. The use of flange connection, easy to run, run, drip, leakage problems, greatly increasing the maintenance workload.

Fifth, thermal mass flowmeter (differential temperature)

Advantages 1. Ball valve installation, easy installation and removal. And can be installed with pressure.

2. Based on King's law, direct measurement of mass flow. The measured value is not affected by pressure and temperature.

3. The response is rapid.

4. Large range of measuring range, minimum pipeline installation can measure the flow of 8.8mm pipe, the maximum can be measured to 30''

5. Plug-in type flow meter, a flow meter can be used to measure a variety of pipe diameters.

Disadvantages 1. The accuracy is not as good as other types of flowmeters, typically 3%.

2. The narrow scope of application can only be used to measure dry non-explosive gases such as compressed air, nitrogen, argon and other neutral gases.