Dinghua Tuning Fork Lecture Hall | Common Faults and Solutions for Tuning Fork Level Switches

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This post was last edited by Xidian Huahua Electronics on 2021-11-4 at 10:29. Fork-type level switches have a long service life, but some faults may occur during operation. Failure symptoms mainly occur in electronic components, power supplies, installation locations, and vibrating fork bodies. This article provides a detailed explanation of the common faults and troubleshooting methods for fork-type level switches. Faults in tuning fork level switches can be mainly divided into two categories: incorrect reports during dry-run protection or overflow protection, and red light flashing as an alarm indication. An error report occurs during dry-run protection or overflow protection. (1) Is the operating voltage too low? Please check and adjust the operating voltage. (2) Damage to electronic components. Please toggle the high/low mode switch; when the instrument switches as a result, the vibrating fork may be covered by debris or suffer mechanical damage. If the switch function remains faulty despite the correct operating mode, please send the instrument for repair. Alternatively, toggle the high/low mode switch; if the gauge does not change mode thereafter, it indicates that the electronic component is damaged, and the component should be replaced. (3) Incorrect installation location. Please install the instrument in a location within the container where there are no dead zones or unintended accumulation of solid materials. (4) There are attachments on the fork. Check the fork body for any attachments; if there are any, remove them. (5) Incorrect high/low mode selection. Please reset the high and low mode correctly (overflow protection, dry operation protection). The indicator light flashes red as an alarm signal: (1) The fork is damaged. Please check whether the fork body is damaged or severely corroded. (2) Electronic components are damaged. Please replace the electronic components. (3) Other components of the instrument are damaged. Please replace the gauge or send it back for repair. When a problem occurs with a fork-type level switch, we should analyze the cause of the fault based on the type of issue that has arisen, take appropriate measures to resolve it, and ensure the smooth operation of the fork-type level switch. Appendix: The “Seven-Step Method” for Repairing Instrument Failures. Seven basic methods: observe, listen, touch, smell, measure, check, and judge. 1. Observe – Examine the condition of various components, look for common issues such as leaks, pipeline vibrations, check fault codes, and review historical trends. 2. Listening—abnormal noises from the equipment, common equipment alarm sounds, operating noises of the equipment, air leaks, and other abnormal sounds. 3. Feel – Check for abnormal conditions such as equipment vibration, overheating, or freezing blockages. 4. Smell—unusual odors from the equipment; the most common causes are severe overheating and short circuits in the equipment. 5. Measurement—Use a multimeter to measure the supply voltage, current, insulation resistance, and other parameters of the instrumentation equipment. 6. Check – consult technical documentation to find out the meaning of fault codes and relevant information on those faults. 7. Judgment—Conduct analytical evaluation by integrating abnormal phenomena to determine the cause of the fault. Detailed Explanation of the Basic Methods 1. Observe: Carefully examine the operation of various components of the instrumentation equipment, paying special attention to any signs of leakage, as well as the display windows on the instruments. (1) Instrumentation equipment: Check all pipelines of the instrumentation equipment for cracks, damage, frosting, and condensation ； To check for leaks at the joint connections, soapy water, a clean soft cloth, or soft paper can be used to wipe the welded areas of the pipes and the joint connections, in order to observe whether there is any air or liquid leakage and thus determine if a leak exists and whether the equipment is operating smoothly. (2) Electrical circuit: Check whether there are any indications or alarms on the display windows of the instrument equipment, examine whether the insulation of the wires is intact, whether there are any breaks in the circuit boards, whether the connections are loose, and whether there are any signs of water intrusion or corrosion that could cause damage, in order to assess the performance of the electrical circuit. 2. Listen: With the power turned on and off, listen carefully to the operating sounds of the instruments and equipment to check whether they are normal, and to identify any abnormal sounds or alarm signals. (1) Instrumentation equipment: Check whether the operating sound of the instrumentation equipment is normal, whether the moving mechanisms function smoothly, and whether there is any vibration in the instrumentation equipment. (2) Electrical circuit: Check whether there are any discharge sounds or other unusual noises inside the listening device. 3. Touch: Use your hand to touch relevant parts of the instrumentation equipment to feel their temperature, vibration, etc. If there are any significant differences, it indicates that something is abnormal. (1) Instrumentation equipment: Touch the instrumentation equipment itself and the pipelines to check whether they are at a normal temperature. (2) Electrical circuit: Touch the relevant wires and chips to check for any heating (this applies to instruments with a voltage of 24V or less); you can also touch the temperature sensors and pressure sensors to verify their performance. 4. Smell: Use the nose to detect any leaks in the surroundings or unusual odors emitted by the equipment. (1) Instrumentation equipment: In the case of leaks in the instrument pipelines, using the sense of smell can help locate the faulty pipeline. (Applicable to media with unpleasant odors) (2) Electrical circuit: Mainly check for any smell of burning in the equipment as well as any odor resulting from heat generation in the equipment. 5. Measurement: Use equipment of the same model or with identical parameters for measurement; specialized testing instruments and multimeters are used to measure the electrical parameters of key components. (1) Instrumentation equipment, used with other alternative devices to check whether the measured parameters are consistent with those displayed by the device under suspicion. (2) In electrical circuits, in order to accurately determine the nature and location of faults, it is often necessary to use instruments and meters to check the performance parameters and condition of the equipment. Use a multimeter to measure the supply voltage, the voltage of each terminal with respect to ground, as well as the current and signal status to ensure they meet the requirements. 6. Check: Review historical trend alarm records, search for relevant information, and look up technical documents. (1) For instrumentation equipment, check whether it meets the requirements of the production process, as well as examine the performance parameters of those devices. (2) Search for recent production records, historical trend alarm records, the meanings of relevant technical specifications and instrument failure codes, as well as the corresponding handling methods and calculation methods. 7. Judgment: The results obtained through the various inspection methods mentioned above generally can only reflect a certain local condition. The various components of instrumentation equipment are interconnected and influence one another; a single fault phenomenon can have multiple causes, and one cause can lead to several different faults. Therefore, a comprehensive comparative analysis of the local factors is necessary in order to accurately determine the nature and location of the fault. If the pressure transmitter fails or gets clogged, it will cause abnormal pressure in the controlled process, resulting in a low pressure level. However, changes in pressure at the controlled entity inevitably cause the valves in the control loop to operate, resulting in either too high or too low system pressure, which can cause damage to the system or even lead to accidents. Therefore, it is possible to carefully determine whether the fault lies with the valves or with the pressure transducer by analyzing the symptoms of the fault. Seven common faults: leakage, blockage, interruption, short circuit, burnout, jamming, and poor contact. 1. Leakage: Air leakage from the pressure-taking port of the sensing element, and electrical leakage in the wiring. 2. Blockage: Blockage in the pressure-taking ports of the sensing elements, as well as blockages in the oil and gas circuits. 3. Open circuit: The sensing element is open-circuited, and both the power supply and signal circuits are open-circuited. 4. Short circuit: Short circuit in the sensing element, as well as short circuits in the power and signal circuits. 5. Burning: Components are damaged or destroyed by external heat, or the equipment is damaged due to a short circuit. 6. Card: The moving mechanism of the instrument equipment is stuck, resulting in uneven operation. 7. Poor contact: Loose connections in the wiring of the instrumentation equipment lead to abnormal operation and incorrect readings of the equipment. Detailed Explanation of Common Fault Phenomena: Most failures in measuring instruments do not occur without any reason; there are always precursor signs to such failures. Some failures are caused by the instruments themselves, while others are due to external factors. The common fault phenomena in measuring instruments include the following 7 types. 1. Leakage: Leakage is a common issue with production equipment. (1) Vibration of the pipelines in instrument equipment, thermal expansion and contraction, external forces, stress, as well as equipment defects can all cause leaks in these pipelines. This type of fault is relatively simple to diagnose; it accounts for over 30% of all instrument failures, and it is also the easiest type of fault to identify. Such faults can generally be resolved. It accounts for a significant proportion in production operations; leaks can occur whenever instrumentation equipment comes into contact with the medium being measured. (2) Leakage current in electrical circuits also occurs from time to time; leakage can happen between cables and cable trays, between cables and equipment, as well as between different cables. This phenomenon is generally caused by cables being installed improperly, resulting in damage to their insulation, or by improper wiring, which leads to grounding leakage between the cables, the equipment, and the junction boxes. 2. Blockage: In the pressure-taking pipelines of instrumentation equipment, impurities in the system can easily enter these pipelines and block the pressure-taking ports; some media are prone to crystallization, which can also block these ports. In winter, the instrumentation pipelines are susceptible to freezing and blockage as well. Blockages generally occur in winter, or with media that are prone to crystallization or contain dirt. This fault is relatively simple; the failure rate of instruments affected by it is over 20%, and it is also an easy-to-diagnose type of fault. Basically, this fault can always be resolved. Second only to leakage faults in terms of its impact on the production process, blockage can occur whenever instrumentation equipment comes into contact with the measured medium. 3. Breakage: Breakage generally refers to a break in an electrical circuit, such as a broken power cable or signal line; the fault occurs due to external forces or stress, and this type of fault is relatively easy to diagnose. However, it is difficult to locate the breakpoints; these points are usually at the connections of the wires, at the areas where the wires are under stress, and near the fittings used for routing the wires. In the case of instrument wiring, breaks or freezes can also occur from time to time. Generally, it is possible to reconfigure the wiring when a wire breaks, with the failure rate of instrument equipment remaining below around 5%. For instrument equipment, there are device failures such as disconnection of the instrument mechanism, breakage of the valve stem, and disconnection of the feedback rod. 4. Short circuit: A short circuit generally refers to a short in an electrical circuit, such as a short in the power supply or signal circuits, or a short between the power lines and signal lines. Faults can occur due to external forces and stresses. Such faults are relatively easy to identify, but it is difficult to locate the point of the short circuit. The possible locations include circuit connections, points where the circuit is under stress, and accessories related to the cable conduits. This also occurs from time to time with instrument circuits; when it’s difficult to locate a short circuit in the usual circuits, it’s generally possible to reconfigure the wiring. The failure rate of instrument equipment is around 10%. 5. Burning: Components can be damaged by external heat, or equipment can be destroyed due to short circuits; water entering the equipment or excessive voltage can also cause internal components to fail, leading to damage to the equipment and its wiring. This type of fault is relatively easy to diagnose, but repair is difficult. Problems also occur frequently with the instrumentation circuits; generally, when the equipment is damaged, it needs to be replaced, with a failure rate of around 5% for instrumentation devices. 6. Jamming: The moving mechanisms of instrumentation devices operate smoothly, but this issue is mainly evident in the valve control mechanisms. This fault is relatively easy to identify, yet there are many possible causes for the jamming. For example ； Issues such as jamming inside the valve core, excessive resistance in the valve stem, and low air supply pressure can cause sticking in all the moving parts of the operating components from time to time. It occurs frequently during the production of instruments, with a failure rate of 10%. This type of failure is relatively common in valve equipment, and most of these failures can be resolved by lubrication. 7. Poor contact: Loose connections in the wiring of the instrumentation equipment can cause the equipment to operate abnormally and give incorrect readings. This issue is mainly due to poor contact at the wiring joints; it’s not easy to detect, but it is difficult to identify. Poor contact can occur in the wiring circuits of all measuring instruments, caused not only by external wires but also by the internal wiring of the instruments themselves. Some of these failures are caused by vibrations that lead to loose screws in the wiring, resulting in poor connections. Additionally, inadequate maintenance can cause oxidation of the connection terminals, which also leads to poor connections. It is necessary to carefully determine whether the fault is indeed due to poor wiring connections. Faults related to instrumentation equipment account for around 20% of all such failures. Common fault symptoms of poor contact include high readings, low readings, and fluctuations; generally, fluctuations occur (with rough curves being typical). For fault diagnosis, one should consider various aspects, mainly drawing on books, experience, and the methods of others. Keep more records and think more about fault issues to facilitate the rapid resolution of similar faults; by taking into account various factors such as process parameters, ambient temperature, and weather conditions, an effective approach to quickly diagnosing faults can be achieved. For example, natural factors can cause the equipment temperature to be too high or too low. Measurement temperature of the compressor ； A temperature difference of around 5 degrees occurs between night and day, while the difference between winter and summer is about 10 degrees; this is normal and not due to a malfunction in the instruments. Appendix source: Instrument Circle