Electromagnetic flowmeters will inevitably have some small errors and failures during the use process. It is not enough for us to simply perform daily maintenance and maintenance. We should still learn some frequent minor failures and some simple handling methods.Next, the editor will introduce the troubleshooting plan of the electromagnetic flowmeter in the production of acetic acid.
1 The medium contains bubbles and there is a measurement failure
The medium absorbs gas from the outside or the dissolved gas in the medium transforms into free bubbles are two ways to generate bubble-like gas in the liquid.If there are large air bubbles in the medium, the whole electrode will be covered when the air bubbles pass through the electrode, so that the flow signal input circuit will be opened instantaneously, so the output signal will fluctuate.To determine the cause of this fluctuation, you can do this by cutting off the loop current of the magnetic field. After cutting off, if the flowmeter still displays and is still in a fluctuating state, it proves that the presence of air bubbles in the medium will cause the electromagnetic flowmeter to fluctuate.Use a pointer multimeter to measure the electrode resistance of the electromagnetic flowmeter, and you will find that the loop resistance of the electrode of the electromagnetic flowmeter is higher than the normal resistance value.
If the air enters the measured medium due to the installation position of the electromagnetic flowmeter, if the gas is stored due to the installation of the electromagnetic flowmeter at the high point of the piping system, or the flowmeter fluctuates due to the inhalation of air from the outside, the electromagnetic flowmeter needs to be replaced. The location modification is installed at the lowest point of the pipeline, or installed with a U-shaped pipe.However, in some cases, due to the large caliber of the electromagnetic flowmeter or the installation position is not easy to change, it can be solved by installing an air collection bag and an exhaust valve upstream of the flowmeter.
2 The medium is not full
Occasionally, there will be a part-full pipe phenomenon in daily production.This phenomenon can be seen as a typical case of a liquid containing air bubbles.When the electrode level is lower than the medium liquid level, it is ideal to use straight pipe sections before and after the flowmeter, and the measurement data is relatively stable.However, the gas volume in the upper half of the tube is also counted as the medium flow rate, so the measurement error in this case is relatively large; when the electrode level is higher than the medium liquid level, the measurement circuit of the electromagnetic flowmeter is in an open state, and the measured data Seriously distorted.The following methods can be used to deal with the failure caused by the non-full pipe of this medium: try to install the electromagnetic flowmeter on the vertical pipeline flowing from bottom to top; in actual production, the electromagnetic flowmeter needs to be installed horizontally, in this case it should be installed on the pipeline The lowest end of zui, and the electrode axis of the electromagnetic flowmeter is parallel to the horizon, (otherwise the sediment will cover the electrode at the lower position); in order to avoid negative pressure in the measuring tube, the sensor of the flowmeter should be installed downstream of the pump, Upstream of the control valve; the installation port of the flowmeter sensor should have a certain back pressure and should be far away from the direct discharge port.
However, the most important thing is that it is best to prohibit the medium from being fully filled when the electromagnetic flowmeter is installed.
3 The electrodes of the electromagnetic flowmeter are corroded
Due to the contact with some strong corrosive media during the production of acetic acid, when the electrode material of the electromagnetic flowmeter is improperly selected, the medium will corrode the electrodes of the flowmeter, and eventually cause the sensor to fail.As a result, flowmeter output fluctuations occur.Only when the electrode is corroded and the flowmeter fails, we can find that the electrode material is not corrosion-resistant. The performance problem of this material itself cannot be identified before it is used.Therefore, only a new electrode can be replaced to solve this kind of failure.Therefore, the judgment and treatment of electrode corrosion faults belong to the method of after-the-fact maintenance and treatment.
4 The nature of the liquid to be measured leads to measurement failures
If the conductivity of the measured medium decreases, the output impedance of the electrode will increase. At this time, the impedance of the converter input will cause a load effect, and the flowmeter will produce measurement errors.If the electromagnetic flowmeter has this failure, you can only choose a low-conductivity electromagnetic flowmeter that meets the requirements, or choose a flowmeter with other principles such as an orifice flowmeter.
5 Measurement failure caused by electrode fouling or electrode short circuit of the flowmeter
When the measured liquid contains metal, the electrode of the flowmeter is prone to short circuit, and the measured value of the flowmeter is obviously small or tends to zero.This phenomenon does not occur frequently in daily production runs.When measuring high-viscosity medium, because the medium is easy to adhere and deposit on the tube wall, if the conductivity of the measured liquid is lower than the conductivity of the attached medium, the signal potential of the electrode will be shunted by the precipitation and cannot work normally, and the electrode short circuit phenomenon will occur ; If the precipitated medium is a non-conductive layer, the open-circuit flowmeter will not work properly.If the oxidized rust layer is attached to the lining pipe wall, or the main component is metal sediment, its conductivity is greater than that of the liquid, and the actual flow value will be higher than the flow value measured by the flowmeter; if the sediment is a scale layer such as calcium carbonate , the conductivity of the measured liquid is higher than that of the sediment, and the measured flow value will be smaller than the actual flow.
In order to prevent the sediment in the fluid from affecting the work of the flowmeter, the electrodes of the flowmeter are pointed or hemispherical, which are not easy to stick to protruding, and can be replaced or scraper-type cleaning electrodes.The scraper electrode can be used to manually scrape off the dirt outside the sensor regularly.Alternatively, the measurement circuit can be temporarily disconnected, and a short-term low-voltage high-current is passed between the electrodes to incinerate and remove grease deposits.The method of increasing the liquid flow rate can also be used to clean the adhesion layer on the pipe wall.
6 Asymmetric flow of the medium to be measured
In the case of normal production, the flow velocity of the fluid in the pipeline is axisymmetrically distributed, and the magnetic field is uniform.However, the non-axisymmetric flow velocity distribution of the fluid in the actual pipeline often appears. At this time, the fluid flow direction can be divided into a straight line flow along the pipeline axis, and the volume flow rate of the liquid to be measured is its integral to the cross section of the pipeline; the other is the vortex flow .Due to the influence of the appearance of the vortex on the output of the sensor, the flowmeter will have an error.In order to eliminate the influence of the vortex flow on the flowmeter sensor; the upstream of the flowmeter should have a long enough straight pipe section so that the flow velocity of the fluid can be distributed in concentric circles; the inner diameter of the pipe near the flowmeter should be the same as the inner diameter of the flowmeter, so that the The flow rate is evenly distributed; otherwise, a flow regulator can be installed to partially compensate for the shortage of the upstream straight pipe section.
7 Flowmeter lining deformation leads to measurement fluctuations
The lining of the flowmeter is generally made of fluoroplastics, so the lining of the flowmeter is very easy to deform and cause measurement failures.There are two main reasons for the deformation of the lining: a fluoroplastic lining penetrates into the steam to cause thermal diffusion, usually the lining material, thickness, temperature difference between inside and outside, type of fluid and steam, pipeline pressure and many other factors determine the degree of penetration; two It depends on the process structure of the fluoroplastic lining material itself. Generally, polytetrafluoroethylene is used as the fluoroplastic lining material. The polytetrafluoroethylene material has no adhesive force and can only be combined with the pipe wall by pressing, so the negative pressure pipeline does not use this method. kind of material.
In order to prevent the deformation of the lining, we generally take the following measures: increase the heat insulation thickness between the flange and the coil box, reduce the temperature difference of the fluid and reduce the thermal diffusion, and improve the temperature difference between the inside and outside of the lining to the greatest extent, so that the permeability can be reduced. Measure the condensation of steam in the pipe wall; in addition, thicken the thickness of the PTFE lining or replace it with another type of lining.
8 External electromagnetic interference
There are interference sources such as pipeline stray current, static electricity, electromagnetic waves and magnetic fields in the production site.The flow signal of the electromagnetic flowmeter is very small, and it is very easy to be interfered by external electromagnetic, which affects the normal operation of the electromagnetic flowmeter.The so-called electric field interference refers to the abnormal fluctuation of the output signal after the potential balance in the measuring tube of the flowmeter is destroyed by noise.
Electromagnetic flowmeters will inevitably have some small errors and failures during the use process. It is not enough for us to simply perform daily maintenance and maintenance. We should still learn some frequent minor failures and some simple handling methods.Next, the editor will introduce the troubleshooting plan of the electromagnetic flowmeter in the production of acetic acid.
1 The medium contains bubbles and there is a measurement failure
The medium absorbs gas from the outside or the dissolved gas in the medium transforms into free bubbles are two ways to generate bubble-like gas in the liquid.If there are large air bubbles in the medium, the whole electrode will be covered when the air bubbles pass through the electrode, so that the flow signal input circuit will be opened instantaneously, so the output signal will fluctuate.To determine the cause of this fluctuation, you can do this by cutting off the loop current of the magnetic field. After cutting off, if the flowmeter still displays and is still in a fluctuating state, it proves that the presence of air bubbles in the medium will cause the electromagnetic flowmeter to fluctuate.Use a pointer multimeter to measure the electrode resistance of the electromagnetic flowmeter, and you will find that the loop resistance of the electrode of the electromagnetic flowmeter is higher than the normal resistance value.
If the air enters the measured medium due to the installation position of the electromagnetic flowmeter, if the gas is stored due to the installation of the electromagnetic flowmeter at the high point of the piping system, or the flowmeter fluctuates due to the inhalation of air from the outside, the electromagnetic flowmeter needs to be replaced. The location modification is installed at the lowest point of the pipeline, or installed with a U-shaped pipe.However, in some cases, due to the large caliber of the electromagnetic flowmeter or the installation position is not easy to change, it can be solved by installing an air collection bag and an exhaust valve upstream of the flowmeter.
2 The medium is not full
Occasionally, there will be a part-full pipe phenomenon in daily production.This phenomenon can be seen as a typical case of a liquid containing air bubbles.When the electrode level is lower than the medium liquid level, it is ideal to use straight pipe sections before and after the flowmeter, and the measurement data is relatively stable.However, the gas volume in the upper half of the tube is also counted as the medium flow rate, so the measurement error in this case is relatively large; when the electrode level is higher than the medium liquid level, the measurement circuit of the electromagnetic flowmeter is in an open state, and the measured data Seriously distorted.The following methods can be used to deal with the failure caused by the non-full pipe of this medium: try to install the electromagnetic flowmeter on the vertical pipeline flowing from bottom to top; in actual production, the electromagnetic flowmeter needs to be installed horizontally, in this case it should be installed on the pipeline The lowest end of zui, and the electrode axis of the electromagnetic flowmeter is parallel to the horizon, (otherwise the sediment will cover the electrode at the lower position); in order to avoid negative pressure in the measuring tube, the sensor of the flowmeter should be installed downstream of the pump, Upstream of the control valve; the installation port of the flowmeter sensor should have a certain back pressure and should be far away from the direct discharge port.
However, the most important thing is that it is best to prohibit the medium from being fully filled when the electromagnetic flowmeter is installed.
3 The electrodes of the electromagnetic flowmeter are corroded
Due to the contact with some strong corrosive media during the production of acetic acid, when the electrode material of the electromagnetic flowmeter is improperly selected, the medium will corrode the electrodes of the flowmeter, and eventually cause the sensor to fail.As a result, flowmeter output fluctuations occur.Only when the electrode is corroded and the flowmeter fails, we can find that the electrode material is not corrosion-resistant. The performance problem of this material itself cannot be identified before it is used.Therefore, only a new electrode can be replaced to solve this kind of failure.Therefore, the judgment and treatment of electrode corrosion faults belong to the method of after-the-fact maintenance and treatment.
4 The nature of the liquid to be measured leads to measurement failures
If the conductivity of the measured medium decreases, the output impedance of the electrode will increase. At this time, the impedance of the converter input will cause a load effect, and the flowmeter will produce measurement errors.If the electromagnetic flowmeter has this failure, you can only choose a low-conductivity electromagnetic flowmeter that meets the requirements, or choose a flowmeter with other principles such as an orifice flowmeter.
5 Measurement failure caused by electrode fouling or electrode short circuit of the flowmeter
When the measured liquid contains metal, the electrode of the flowmeter is prone to short circuit, and the measured value of the flowmeter is obviously small or tends to zero.This phenomenon does not occur frequently in daily production runs.When measuring high-viscosity medium, because the medium is easy to adhere and deposit on the tube wall, if the conductivity of the measured liquid is lower than the conductivity of the attached medium, the signal potential of the electrode will be shunted by the precipitation and cannot work normally, and the electrode short circuit phenomenon will occur ; If the precipitated medium is a non-conductive layer, the open-circuit flowmeter will not work properly.If the oxidized rust layer is attached to the lining pipe wall, or the main component is metal sediment, its conductivity is greater than that of the liquid, and the actual flow value will be higher than the flow value measured by the flowmeter; if the sediment is a scale layer such as calcium carbonate , the conductivity of the measured liquid is higher than that of the sediment, and the measured flow value will be smaller than the actual flow.
In order to prevent the sediment in the fluid from affecting the work of the flowmeter, the electrodes of the flowmeter are pointed or hemispherical, which are not easy to stick to protruding, and can be replaced or scraper-type cleaning electrodes.The scraper electrode can be used to manually scrape off the dirt outside the sensor regularly.Alternatively, the measurement circuit can be temporarily disconnected, and a short-term low-voltage high-current is passed between the electrodes to incinerate and remove grease deposits.The method of increasing the liquid flow rate can also be used to clean the adhesion layer on the pipe wall.
6 Asymmetric flow of the medium to be measured
In the case of normal production, the flow velocity of the fluid in the pipeline is axisymmetrically distributed, and the magnetic field is uniform.However, the non-axisymmetric flow velocity distribution of the fluid in the actual pipeline often appears. At this time, the fluid flow direction can be divided into a straight line flow along the pipeline axis, and the volume flow rate of the liquid to be measured is its integral to the cross section of the pipeline; the other is the vortex flow .Due to the influence of the appearance of the vortex on the output of the sensor, the flowmeter will have an error.In order to eliminate the influence of the vortex flow on the flowmeter sensor; the upstream of the flowmeter should have a long enough straight pipe section so that the flow velocity of the fluid can be distributed in concentric circles; the inner diameter of the pipe near the flowmeter should be the same as the inner diameter of the flowmeter, so that the The flow rate is evenly distributed; otherwise, a flow regulator can be installed to partially compensate for the shortage of the upstream straight pipe section.
7 Flowmeter lining deformation leads to measurement fluctuations
The lining of the flowmeter is generally made of fluoroplastics, so the lining of the flowmeter is very easy to deform and cause measurement failures.There are two main reasons for the deformation of the lining: a fluoroplastic lining penetrates into the steam to cause thermal diffusion, usually the lining material, thickness, temperature difference between inside and outside, type of fluid and steam, pipeline pressure and many other factors determine the degree of penetration; two It depends on the process structure of the fluoroplastic lining material itself. Generally, polytetrafluoroethylene is used as the fluoroplastic lining material. The polytetrafluoroethylene material has no adhesive force and can only be combined with the pipe wall by pressing, so the negative pressure pipeline does not use this method. kind of material.
In order to prevent the deformation of the lining, we generally take the following measures: increase the heat insulation thickness between the flange and the coil box, reduce the temperature difference of the fluid and reduce the thermal diffusion, and improve the temperature difference between the inside and outside of the lining to the greatest extent, so that the permeability can be reduced. Measure the condensation of steam in the pipe wall; in addition, thicken the thickness of the PTFE lining or replace it with another type of lining.
8 External electromagnetic interference
There are interference sources such as pipeline stray current, static electricity, electromagnetic waves and magnetic fields in the production site.The flow signal of the electromagnetic flowmeter is very small, and it is very easy to be interfered by external electromagnetic, which affects the normal operation of the electromagnetic flowmeter.The so-called electric field interference refers to the abnormal fluctuation of the output signal after the potential balance in the measuring tube of the flowmeter is destroyed by noise.
In order to reduce the interference of the external magnetic field to the flowmeter, we need to install the electromagnetic flowmeter sensor at a position away from the strong magnetic field source.In addition, enhanced shielding measures are taken to prevent interference from strong electric fields.It is also possible to insulate the connection between the electromagnetic flow sensor and the pipeline.
9 Failures caused by other reasons
1) Lightning strike.After being struck by lightning, the electromagnetic flowmeter is easy to induce high voltage and current in the line, which will damage the flow agent.
2) Changes in environmental conditions.Once the working environment conditions of the flowmeter change and new interference sources appear during operation, the normal operation of the meter will be disturbed, and the output signal of the flowmeter will fluctuate.
In recent years, with the rapid development and continuous improvement of modern technology, the technology of instrument protection is also improving day by day. The electromagnetic flowmeter itself rarely fails, so users should pay attention to using the correct method when installing and using it. , with more daily maintenance, you can use it with confidence.
In order to reduce the interference of the external magnetic field to the flowmeter, we need to install the electromagnetic flowmeter sensor at a position away from the strong magnetic field source.In addition, enhanced shielding measures are taken to prevent interference from strong electric fields.It is also possible to insulate the connection between the electromagnetic flow sensor and the pipeline.
9 Failures caused by other reasons
1) Lightning strike.After being struck by lightning, the electromagnetic flowmeter is easy to induce high voltage and current in the line, which will damage the flow agent.
2) Changes in environmental conditions.Once the working environment conditions of the flowmeter change and new interference sources appear during operation, the normal operation of the meter will be disturbed, and the output signal of the flowmeter will fluctuate.
In recent years, with the rapid development and continuous improvement of modern technology, the technology of instrument protection is also improving day by day. The electromagnetic flowmeter itself rarely fails, so users should pay attention to using the correct method when installing and using it. , with more daily maintenance, you can use it with confidence.
