Chongqing Huanyu Automobile Sales Company , https://www.nbhuanyuauto.com
Summarizing many years of experience and lessons learned that the causes of errors in electromagnetic flowmeters are mainly the following aspects.
First, the electromagnetic flowmeter tube liquid is not full due to lack of back pressure or poor position of the flow sensor installation, resulting in the measurement tube is not filled with liquid, the phenomenon of failure due to the degree of non-full and flow conditions have different performance. If a small amount of gas is stratified or wavy in the water pipe, the fault phenomenon is manifested as an increase in the error, that is, the flow measurement is inconsistent with the actual value; if the flow is a bubble flow or a plug flow, the fault phenomenon is not consistent with the measured value and the actual value. In addition, output shaking will occur due to the gas phase covering the surface of the electrode for the moment; if the flow area of ​​the cross-section gas increases in the stratified flow of the horizontal pipe, that is, the degree of liquid underfilling increases, output shaking will also occur if the liquid is not full. The situation is so serious that if the liquid level is below the electrode, an overfull-scale phenomenon will occur. The cause of such failures is often encountered in the case of after-sales service in manufacturing plants. It is an engineering design mistake.
Second, the liquid contains solids containing solids such as powder, granules or fibers, the possible failures are; 1 slurry noise; 2 electrode surface contamination; 3 conductive deposits or insulating deposits cover the electrode or lining; 4 lining is worn Or covered by sediments, the circulation cross-sectional area is reduced. If the electromagnetic lining of the measuring tube of the electromagnetic flow sensor is deposited with conductive material, the flow signal will be short-circuited and the instrument will fail. As the conductive material is gradually deposited, this type of fault usually does not appear in the commissioning period, but it will only appear after a period of operation.
Third, there may be crystal liquid, electromagnetic flowmeter should be used with caution. Some easy-to-crystallize chemical materials can be normally measured under normal temperature conditions. Since the conduits for transporting fluids have good heat-tracing insulation, they will not crystallize during insulation work. However, it is difficult for the measurement tube of the electromagnetic flow sensor to perform thermal insulation. Therefore, when the fluid flows through the measurement tube, it is easy to cause a solid layer on the inner wall due to the temperature drop. Because there are also crystallization issues due to the use of other principles of flow meter measurement, there is no other better way to use a "ring" electromagnetic flow sensor with a very short length of measuring tube, and the upstream of the flow meter Heat insulation is strengthened. In the pipe connection method, it is convenient to disassemble and disassemble the flow sensor, and it can be easily removed and maintained once it is crystallized.
Fourth, the electrode and grounding ring caused by improper material selection Problems caused by the material and the measured medium does not match the electromagnetic flowmeter caused by failure and the media contact parts are the electrode and the grounding ring, matching failure in addition to corrosion problems, as long as the electrode Surface effect. Surface effects should be: 1 chemical reaction (the surface of the formation of dull words, etc.); 2 electrochemical and polarization phenomena (electric potential); 3 catalyst (electrode surface to generate aerosol, etc.). Ground loops also have these effects, but the impact is less.
5. Problems caused by the liquid conductivity exceeding the allowable range The liquid conductivity may be shaken if it approaches the lower limit. Because the lower limit value specified by the manufacturer's instrument specification is the lowest value that can be measured under various conditions of good use, and the actual conditions cannot be ideal, so many low-level distilled or deionized waters are encountered. Its conductivity is close to the lower limit value of 5 specified by the electromagnetic flowmeter specification, but output shaking occurs during use. It is generally considered that the lower limit of the conductivity that can be measured stably is 1 to 2 orders of magnitude higher. The conductivity of the liquid can be found in the relevant manuals.
The five factors that cause the error of the electromagnetic flowmeter are many. The electromagnetic flowmeter has many advantages and is widely used. However, if the type is selected, installed and used improperly, the error will increase, the indication value will be unstable, and even the body will be damaged.
Summarizing many years of experience and lessons learned that the causes of errors in electromagnetic flowmeters are mainly the following aspects.
First, the electromagnetic flowmeter tube liquid is not full due to lack of back pressure or poor position of the flow sensor installation, resulting in the measurement tube is not filled with liquid, the phenomenon of failure due to the degree of non-full and flow conditions have different performance. If a small amount of gas appears stratified or wavy flow in the water pipe, the fault phenomenon shows an increase in error, that is, the measured value of the flow does not match the actual value; if the flow is a bubble flow or a plug flow, the fault phenomenon does not match the measured value and the actual value. In addition, output shaking will occur due to the gas phase covering the surface of the electrode for the moment; if the flow area of ​​the cross-section gas increases in the stratified flow of the horizontal pipe, that is, the degree of liquid underfilling increases, output shaking will also occur if the liquid is not full. The situation is so serious that if the liquid level is below the electrode, an overfull-scale phenomenon will occur. The cause of such failures is often encountered in the case of after-sales service in manufacturing plants. It is an engineering design mistake.
Second, the liquid contains solids containing solids such as powder, granules or fibers, the possible failures are; 1 slurry noise; 2 electrode surface contamination; 3 conductive deposits or insulating deposits cover the electrode or lining; 4 lining is worn Or covered by sediments, the circulation cross-sectional area is reduced. If the electromagnetic lining of the measuring tube of the electromagnetic flow sensor is deposited with conductive material, the flow signal will be short-circuited and the instrument will fail. As the conductive material is gradually deposited, this type of fault usually does not appear in the commissioning period, but it will only appear after a period of operation.
Third, there may be crystal liquid, electromagnetic flowmeter should be used with caution. Some easy-to-crystallize chemical materials can be normally measured under normal temperature conditions. Since the conduits for transporting fluids have good heat-tracing insulation, they will not crystallize during insulation work. However, it is difficult for the measurement tube of the electromagnetic flow sensor to perform thermal insulation. Therefore, when the fluid flows through the measurement tube, it is easy to cause a solid layer on the inner wall due to the temperature drop. Because there are also crystallization issues due to the use of other principles of flow meter measurement, there is no other better way to use a "ring" electromagnetic flow sensor with a very short length of measuring tube, and the upstream of the flow meter Heat insulation is strengthened. In the pipe connection method, it is convenient to disassemble and disassemble the flow sensor, and it can be easily removed and maintained once it is crystallized.
Fourth, the electrode and grounding ring caused by improper material selection Problems caused by the material and the measured medium does not match the electromagnetic flowmeter caused by failure and the media contact parts are the electrode and the grounding ring, matching failure in addition to corrosion problems, as long as the electrode Surface effect. Surface effects should be: 1 chemical reaction (the surface of the formation of dull words, etc.); 2 electrochemical and polarization phenomena (electric potential); 3 catalyst (electrode surface to generate aerosol, etc.). Ground loops also have these effects, but the impact is less.
5. Problems caused by the liquid conductivity exceeding the allowable range The liquid conductivity may be shaken if it approaches the lower limit. Because the lower limit value specified by the manufacturer's instrument specification is the lowest value that can be measured under various conditions of good use, and the actual conditions cannot be ideal, so many low-level distilled or deionized waters are encountered. Its conductivity is close to the lower limit value of 5 specified by the electromagnetic flowmeter specification, but output shaking occurs during use. It is generally considered that the lower limit of the conductivity that can be measured stably is 1 to 2 orders of magnitude higher. The conductivity of the liquid can be found in the relevant manual. If there is no ready-made data, the conductivity can be measured with a conductivity meter. However, sometimes there are cases in which samples are taken from the pipeline to be considered available in the laboratory and the actual electromagnetic flowmeter cannot be operated. This is because there is already a difference between the liquid and the liquid in the pipeline when the conductivity is measured. For example, if the liquid has absorbed CO2 or NO in the atmosphere and carbonic acid or nitric acid is generated, the electrical conductivity increases. For noise slurry containing particles or fiber fluids, the method of increasing the excitation frequency can effectively improve the output sloshing. Some frequency-modulated IFM3080F DN300 electromagnetic flowmeters measure the concentration of 3.5% corrugated cardboard slurry and measure instantaneous instantaneous flow fluctuations at different excitation frequencies in the field. When the frequency is low, when the frequency is 50/32 Hz, the shaking is as high as 10.7%; the frequency is increased to 50/2Hz, and the shaking is reduced to 1.9%, and the effect is very obvious.
Missing off-the-shelf data can be sampled with a conductivity meter. However, sometimes there are cases in which samples are taken from the pipeline to be determined by the laboratory to be considered usable and the actual electromagnetic flowmeter cannot be operated. This is because there is already a difference between the liquid and the liquid in the pipeline when the conductivity is measured. For example, if the liquid has absorbed CO2 or NO in the atmosphere and carbonic acid or nitric acid is generated, the electrical conductivity increases. For noise slurry containing particles or fiber fluids, the method of increasing the excitation frequency can effectively improve the output sloshing. Some frequency-modulated IFM3080F DN300 electromagnetic flowmeters measure the concentration of 3.5% corrugated cardboard slurry and measure instantaneous instantaneous flow fluctuations at different excitation frequencies in the field. When the frequency is low, when the frequency is 50/32 Hz, the shaking is as high as 10.7%; the frequency is increased to 50/2Hz, and the shaking is reduced to 1.9%, and the effect is very obvious.
Five factors that cause errors in electromagnetic flowmeters
Electromagnetic flowmeters have many advantages and are widely used. However, if they are selected, installed, or used improperly, they will cause an increase in errors, unstable display values, and even damage to the body.