Differential pressure transmitter failure analysis
[Abstract] The differential pressure transmitter can prevent the medium in the pipeline from directly entering the transmitter, and the pressure-sensitive diaphragm and the transmitter are connected by the capillary filled with fluid. It is used to measure the level, flow and pressure of liquids, gases or vapors, and then convert it into a 4-20 mADC signal output. In today's widely used, differential pressure transmitters also leak a lot of problems, the problem can not be resolved in time will affect the production. This article briefly introduced the basic principles of differential pressure transmitter and the use of matters needing attention, focusing on the common differential pressure transmitter failure analysis method and positive pressure tube leakage failure.
Foreword With the economic development and the improvement of industrial automation, differential pressure transmitter has been widely used in steel manufacturing, food hygiene, chemical industry, papermaking and other enterprises. In the application process shows the advantages of flow measurement, differential pressure transmitter daily measurement methods are the following: 1 By using the pressure difference to achieve the height of the measurement liquid, the pressure difference is generated by the liquid's own gravity; 2 and other Components used in combination to achieve the purpose of measuring the flow of liquid, such as: can be combined with the throttling element, use the differential pressure value generated before and after the throttling element to measure the liquid flow; 3 directly measure the pressure difference of different pipes, tank liquid. In application, the application technology of differential pressure transmitter is also increasing. Of course, in the application process, failures often occur. If the maintenance personnel fail to solve the problems due to insufficient levels during the application, the production schedule and the normal use of the instrument will be affected to varying degrees. It can be seen that the role of on-site maintenance personnel is very important, which also provides on-site maintenance personnel with a stage to continuously improve their own technology.
1 basic principle of differential pressure transmitter Design principle: Differential pressure transmitter measurement result is the pressure difference, that is â–³ P = Ïg â–³ h. Since the tank is often cylindrical, the area s of its cross-section circle is constant, then, the weight G = â–³ P · s = Ïg â–³ h · S, S is constant, G and â–³ P is proportional to the relationship. That is, as long as the ΔP value is accurately detected, and inversely proportional to the height Δh, even if the oil volume expands or contracts when the temperature changes, the actual liquid level rises or falls, and the detected pressure remains unchanged.
If the user needs to display the actual liquid level, media temperature compensation can also be introduced to resolve.
Working principle: A space is divided into two chambers with a sensitive element (multiple membrane box). When pressure is introduced into the two chambers, respectively, the sensor generates a displacement (or displacement) under the combined action of the two pressures. This displacement is proportional to the pressure difference between the two chambers (differential pressure), and this displacement is converted into It can reflect the standard signal output of differential pressure. In addition, in the actual construction, the structure of the sensor, the form of the chamber, the manner of displacement conversion, and the format of the standard signal are many.
2 Precautions during the use of differential pressure transmitters The following points should be noted when using differential pressure transmitters: 1 Do not apply more than 36V to the transmitter, resulting in damage to the transmitter. 2 The measured medium is not allowed to freeze, otherwise it will damage the sensor element isolation diaphragm, resulting in damage to the transmitter. If necessary, the temperature of the transmitter must be protected against icing. 3 Do not touch the diaphragm with a hard object, resulting in damage to the isolation diaphragm. 4 When measuring steam or other high-temperature media, use a heat pipe to connect the transmitter and the pipe together and use the pressure on the pipe to transfer it to the transformer. When the measured medium is water vapor, proper amount of water should be injected into the heat pipe to prevent the superheated steam from directly contacting the transmitter and damaging the sensor. 5 When measuring steam or other high-temperature medium, the temperature should not exceed the temperature limit when the transmitter is used. A heat sink must be used above the temperature limit of the transmitter. 6 During the transmission of pressure, attention should be paid to the point where the transmitter and the heat pipe are connected and should not leak. Before starting to use, if the valve is closed, the valve should be opened very carefully and slowly to avoid being tested. The media directly impacts the sensor diaphragm, damaging the sensor diaphragm; the pipeline must be kept clear, deposits in the pipeline will pop up and damage the sensor diaphragm.
3 Common Differential Pressure Transmitter Failure Analysis Methods Any instrument will produce a variety of failure problems during use. All require maintenance, and differential pressure transmitters are no exception. Faults often occur in industrial processes. From the production point of view, how to judge the fault within the first time, find out the problem, and find the solution to the problem is the most important, following the actual work experience of daily maintenance and maintenance, a brief summary of the following methods : 1 direct observation method: Many faults seem more complicated, but often can rely on the experience of maintenance personnel, through direct observation and other direct means to solve the problem quickly. Such as: According to the status quo of the problem, maintenance personnel can observe whether the parts of the equipment are damaged, ask the on-site operators, the operation of the instrument before the malfunction (fire, smoke, odor, power supply changes, lightning, moisture, misuse, error Maintenance), smell whether the instrument has charred odor, touch each component is loose and so on. (Hidden investigation method: After a failure occurs, maintenance personnel find that there are many factors that can cause this failure to occur. At this time, the maintenance personnel need to use appropriate methods to carry out troubleshooting step by step, and to identify the components that are most likely to fail. The other parts are isolated and diagnosed, if the problem is found, further repairs can be performed, if the fault is confirmed not belonging to the part, the next suspect part inquiries should be made, such as: Smart differential pressure transmitter can not be normal Hart remote Communication, the power can be disconnected from the surface of the body, use the method of adding power at the scene for the transmitter power communication, to see if the cable is superimposed on the electromagnetic signal and interfere with the communication.
3 replacement parts method: This method is to remove the suspected faulty parts, replace them with good parts, check whether the instrument is operating normally. For example, if you suspect that the transmitter circuit board has failed, replace it temporarily to determine the cause.
4 Common Failure Analysis Differential pressure transmitters have many types of failures, including parts wear, lack of lubricants, and faults in the pressure guiding tube. The following is a typical example of the most common leakage failures of pressure guiding tubes. Analysis of failures to further elaborate troubleshooting methods and techniques.
problem:
Taking the leakage of positive pressure tube as an example to analyze and analyze the failure phenomenon of leakage of the pressure tube. The flow measurement method for the purification air total pipeline used by a unit's instrument control valve is throttle orifice plate + differential pressure transmitter. The flow rate of the wind when the device is in normal production is basically stable, but in the later production process, the flow of the wind is found to be much lower than the normal value.
Inspection process: After the direct observation, it was found that each circuit signal was in good condition and the secondary instrument was operating normally. The transmitter was sent to the calibration room for calibration and found no abnormalities. Based on the above basic characteristics, maintenance personnel initially suspected that the pressure guiding tube may have failed. After careful examination of the pressure guiding tube, leakage of the positive pressure guiding tube was found. The reason is that the welding seal is not good. As a result, the problem was solved by using a professional welding tool to repair the leaking point of the pressure guiding pipe. Finally, the flow rate of the inspection was restored to normal.
Positive pressure pipe leakage problem analysis: positive pressure pipe leakage phenomenon: the transmitter output decreased, rising and unchanged, the specific analysis is as follows:
When the flow rate rises, influence the output of the transmitter (the output signal of the transmitter itself), set the original flow rate to F1, P1=P1+P1-, FI=K, and F'1 is the change before the change. Output value; set the actual flow after the increase is F2, (ie: F2>FI), F'2=K, F'2 is the transmitter output value after the flow is increased. As the flow increases, the pipe static pressure increases to P0. As the flow rate increases, the actual pressure pipe static pressure decreases to P0', and the positive pressure pipe leakage drops to Ps.
Then: P2+=P1++P0~Ps. P2-=P1-+P0-P0â–¡P2=P2+-P2-=P1+(P0â–¡-Ps) Then when:Poâ–¡=Ps, the positive pressure conduit leaks, and when the flow rate increases, the transmitter output does not change.
When: Poâ–¡>Ps leaks from a positive pressure conduit and the flow rate increases, the transmitter output increases.
When: po -
When the flow rate drops, the actual flow rate after the drop of the output of the transmitter (the output signal of the transmitter itself) is set to F2, that is: F2
Due to the decrease of flow rate, the static pressure of the pipeline decreases by Po. At the same time, due to the decrease of the fluid flow rate, the static pressure of the negative pressure pipe increases by P0′, and the pressure drop of the positive pressure pipe decreases to Ps, then: P2+=P1+−P0-Ps.
P2-=P1--P0+P0□P2=P2+-P2-=P1-(Ps+P0′)
F'2=K=K: When the flow drops, the transmitter output is always smaller than the actual flow.
Concluding remarks The failure is accompanied by the use of the instrument. The failure is not possible. The fear is that the failure has not been repaired in time. Therefore, maintenance techniques and methods are very important. The fault diagnosis method and the analysis process of the common faults in this article are the experience summary of on-site maintenance. The viewpoints in the article can provide some reference for the field maintenance staff or teachers' teaching.
Foreword With the economic development and the improvement of industrial automation, differential pressure transmitter has been widely used in steel manufacturing, food hygiene, chemical industry, papermaking and other enterprises. In the application process shows the advantages of flow measurement, differential pressure transmitter daily measurement methods are the following: 1 By using the pressure difference to achieve the height of the measurement liquid, the pressure difference is generated by the liquid's own gravity; 2 and other Components used in combination to achieve the purpose of measuring the flow of liquid, such as: can be combined with the throttling element, use the differential pressure value generated before and after the throttling element to measure the liquid flow; 3 directly measure the pressure difference of different pipes, tank liquid. In application, the application technology of differential pressure transmitter is also increasing. Of course, in the application process, failures often occur. If the maintenance personnel fail to solve the problems due to insufficient levels during the application, the production schedule and the normal use of the instrument will be affected to varying degrees. It can be seen that the role of on-site maintenance personnel is very important, which also provides on-site maintenance personnel with a stage to continuously improve their own technology.
1 basic principle of differential pressure transmitter Design principle: Differential pressure transmitter measurement result is the pressure difference, that is â–³ P = Ïg â–³ h. Since the tank is often cylindrical, the area s of its cross-section circle is constant, then, the weight G = â–³ P · s = Ïg â–³ h · S, S is constant, G and â–³ P is proportional to the relationship. That is, as long as the ΔP value is accurately detected, and inversely proportional to the height Δh, even if the oil volume expands or contracts when the temperature changes, the actual liquid level rises or falls, and the detected pressure remains unchanged.
If the user needs to display the actual liquid level, media temperature compensation can also be introduced to resolve.
Working principle: A space is divided into two chambers with a sensitive element (multiple membrane box). When pressure is introduced into the two chambers, respectively, the sensor generates a displacement (or displacement) under the combined action of the two pressures. This displacement is proportional to the pressure difference between the two chambers (differential pressure), and this displacement is converted into It can reflect the standard signal output of differential pressure. In addition, in the actual construction, the structure of the sensor, the form of the chamber, the manner of displacement conversion, and the format of the standard signal are many.
2 Precautions during the use of differential pressure transmitters The following points should be noted when using differential pressure transmitters: 1 Do not apply more than 36V to the transmitter, resulting in damage to the transmitter. 2 The measured medium is not allowed to freeze, otherwise it will damage the sensor element isolation diaphragm, resulting in damage to the transmitter. If necessary, the temperature of the transmitter must be protected against icing. 3 Do not touch the diaphragm with a hard object, resulting in damage to the isolation diaphragm. 4 When measuring steam or other high-temperature media, use a heat pipe to connect the transmitter and the pipe together and use the pressure on the pipe to transfer it to the transformer. When the measured medium is water vapor, proper amount of water should be injected into the heat pipe to prevent the superheated steam from directly contacting the transmitter and damaging the sensor. 5 When measuring steam or other high-temperature medium, the temperature should not exceed the temperature limit when the transmitter is used. A heat sink must be used above the temperature limit of the transmitter. 6 During the transmission of pressure, attention should be paid to the point where the transmitter and the heat pipe are connected and should not leak. Before starting to use, if the valve is closed, the valve should be opened very carefully and slowly to avoid being tested. The media directly impacts the sensor diaphragm, damaging the sensor diaphragm; the pipeline must be kept clear, deposits in the pipeline will pop up and damage the sensor diaphragm.
3 Common Differential Pressure Transmitter Failure Analysis Methods Any instrument will produce a variety of failure problems during use. All require maintenance, and differential pressure transmitters are no exception. Faults often occur in industrial processes. From the production point of view, how to judge the fault within the first time, find out the problem, and find the solution to the problem is the most important, following the actual work experience of daily maintenance and maintenance, a brief summary of the following methods : 1 direct observation method: Many faults seem more complicated, but often can rely on the experience of maintenance personnel, through direct observation and other direct means to solve the problem quickly. Such as: According to the status quo of the problem, maintenance personnel can observe whether the parts of the equipment are damaged, ask the on-site operators, the operation of the instrument before the malfunction (fire, smoke, odor, power supply changes, lightning, moisture, misuse, error Maintenance), smell whether the instrument has charred odor, touch each component is loose and so on. (Hidden investigation method: After a failure occurs, maintenance personnel find that there are many factors that can cause this failure to occur. At this time, the maintenance personnel need to use appropriate methods to carry out troubleshooting step by step, and to identify the components that are most likely to fail. The other parts are isolated and diagnosed, if the problem is found, further repairs can be performed, if the fault is confirmed not belonging to the part, the next suspect part inquiries should be made, such as: Smart differential pressure transmitter can not be normal Hart remote Communication, the power can be disconnected from the surface of the body, use the method of adding power at the scene for the transmitter power communication, to see if the cable is superimposed on the electromagnetic signal and interfere with the communication.
3 replacement parts method: This method is to remove the suspected faulty parts, replace them with good parts, check whether the instrument is operating normally. For example, if you suspect that the transmitter circuit board has failed, replace it temporarily to determine the cause.
4 Common Failure Analysis Differential pressure transmitters have many types of failures, including parts wear, lack of lubricants, and faults in the pressure guiding tube. The following is a typical example of the most common leakage failures of pressure guiding tubes. Analysis of failures to further elaborate troubleshooting methods and techniques.
problem:
Taking the leakage of positive pressure tube as an example to analyze and analyze the failure phenomenon of leakage of the pressure tube. The flow measurement method for the purification air total pipeline used by a unit's instrument control valve is throttle orifice plate + differential pressure transmitter. The flow rate of the wind when the device is in normal production is basically stable, but in the later production process, the flow of the wind is found to be much lower than the normal value.
Inspection process: After the direct observation, it was found that each circuit signal was in good condition and the secondary instrument was operating normally. The transmitter was sent to the calibration room for calibration and found no abnormalities. Based on the above basic characteristics, maintenance personnel initially suspected that the pressure guiding tube may have failed. After careful examination of the pressure guiding tube, leakage of the positive pressure guiding tube was found. The reason is that the welding seal is not good. As a result, the problem was solved by using a professional welding tool to repair the leaking point of the pressure guiding pipe. Finally, the flow rate of the inspection was restored to normal.
Positive pressure pipe leakage problem analysis: positive pressure pipe leakage phenomenon: the transmitter output decreased, rising and unchanged, the specific analysis is as follows:
When the flow rate rises, influence the output of the transmitter (the output signal of the transmitter itself), set the original flow rate to F1, P1=P1+P1-, FI=K, and F'1 is the change before the change. Output value; set the actual flow after the increase is F2, (ie: F2>FI), F'2=K, F'2 is the transmitter output value after the flow is increased. As the flow increases, the pipe static pressure increases to P0. As the flow rate increases, the actual pressure pipe static pressure decreases to P0', and the positive pressure pipe leakage drops to Ps.
Then: P2+=P1++P0~Ps. P2-=P1-+P0-P0â–¡P2=P2+-P2-=P1+(P0â–¡-Ps) Then when:Poâ–¡=Ps, the positive pressure conduit leaks, and when the flow rate increases, the transmitter output does not change.
When: Poâ–¡>Ps leaks from a positive pressure conduit and the flow rate increases, the transmitter output increases.
When: po -
When the flow rate drops, the actual flow rate after the drop of the output of the transmitter (the output signal of the transmitter itself) is set to F2, that is: F2
Due to the decrease of flow rate, the static pressure of the pipeline decreases by Po. At the same time, due to the decrease of the fluid flow rate, the static pressure of the negative pressure pipe increases by P0′, and the pressure drop of the positive pressure pipe decreases to Ps, then: P2+=P1+−P0-Ps.
P2-=P1--P0+P0□P2=P2+-P2-=P1-(Ps+P0′)
F'2=K=K: When the flow drops, the transmitter output is always smaller than the actual flow.
Concluding remarks The failure is accompanied by the use of the instrument. The failure is not possible. The fear is that the failure has not been repaired in time. Therefore, maintenance techniques and methods are very important. The fault diagnosis method and the analysis process of the common faults in this article are the experience summary of on-site maintenance. The viewpoints in the article can provide some reference for the field maintenance staff or teachers' teaching.
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