maintenance Related Articles

Overview: The article discusses the importance of maintenance in ensuring the reliability and safety of power electronic systems. It outlines the steps involved in maintenance, including condition observation, anomaly identification, defect diagnosis, and remaining useful life prediction. Power electronic systems are subject to a variety of risks, including catastrophic failures, despite the careful consideration of dependability characteristics during design and control. This is because of the complex and demanding operating settings of power electronic systems. For field applications, power electronic components, converters, and systems must be extremely reliable and safe. What are the steps in maintenance to make the power electronic system more reliable?Preventive maintenance systems are useful ways to guarantee that planned functions are carried out as intended. The steps in maintenance of power electronic system includesCondition observationIdentification of anomaliesDiagnosing defectsRemaining Use Life (RUL) predictionThe above actions coincide with the IEEE standard framework of prognostics and health management for electronic systems. Condition ObservationPower electronics condition observation consists ofIdentification of system parametersPreprocessing dataMining featuresThe data from the condition observation is used to discover informative and hidden patterns that form the foundation for the prognostic and health management applications that follow. Identification of System ParametersIdentification of system parameters involves the gathering of data for important components.Characteristics of power electronic systems includesExtremely small space inside a power moduleExtremely fast switching frequencyRelatively insignificant parameter changes in terms of aging, etc.Because of these characteristics, developing specific hardware for parameter identification is quite a challenging task.A noninvasive approach that uses existing physical signals to indirectly get information or estimate relevant information without the need for additional hardware implementation is one of the more promising methods.Therefore, a sensorless and cost-effective option can be used for condition monitoring, which is good for people who work in industry. In general, there are two types of methods for identifying system parameters:Model-freeModel-based. Preprocessing data and Mining featuresThe goal of data preprocessing and feature mining is to improve the quality of the raw data so that it can be used for applications like problem diagnostics.Improving the quality of data involves the following steps to make it more organized. The steps are as followsData cleaning to minimize noiseData clustering is used to find groups of related data pointsDensity estimation is used to determine the distribution of the dataData compression to reduce the number of features by projecting large-sized data to small-sized dataData fusion to combine various information sources, and moreWhen data preparation and feature mining are done correctly, the performance of the ensuing prognostics and health management applications—such as diagnostic accuracy—can usually be greatly enhanced. Identification of Anomalies and Diagnosing DefectsThe anomaly detection process focuses on identifying unusual patterns and making a binary decision. When the nominal parameters or rated system characteristics exceed the predetermined safety range, it gives an indication.The fault diagnosis finds and identifies the specific failure modes after the unusual changes happen.The classification, regression, or clustering tasks are essentially anomaly detection and fault diagnosis. When a new fault signature arrives, it identifies the fault label based on the learned relationship from the training stage.Anomaly detection and fault diagnosis techniques fall into two categories:Supervised learningUnsupervised learning Remaining Useful Life (RUL) PredictionIn the design phase, lifetime prediction serves to support the characteristics of a population of units known as the ‘Design for Reliability’. It is one of the crucial components of prognostics and health management.The purpose of the estimation of RUL is not to accurately predict the lifespan of a population of units. Based on condition monitoring data, it predicts the remaining lifespan of each single unit in operation. For applications where availability, safety, or reliability are crucial, RUL prediction is used as an extra tool to lower uncertainty.The lifetime estimate is subject to several challenges, such asInaccuracies in model calibrationManufacturing tolerancesDifferences in operational environments and workloadWhen a particular unit is operated in the field, these uncertainties lead to inaccurate reliability estimations. The following areas require greater attention in order to improve the practicality of AI-based RUL prediction techniques for field applications. Quantification of uncertaintyFor RUL prediction, being able to measure uncertainty is more important than for other regression-related tasks, like control functions. Since the RUL is a random variable, quantifying the confidence interval is crucial for making the best decisions.All of these uncertainties—due to population heterogeneity, measurement noise, various operating settings, etc.—should be considered in a workable practical solution. Quantifying the uncertainty using AI algorithms is quite difficult.A few practical options areThe use of particle filters in neural networks (NNs)Bayesian-based artificial intelligence techniques (e.g., Gaussian process, RVM)Monte Carlo methodsStochastic data-drivenStochastic, data-driven approaches are an interesting option to explore. These approaches can naturally yield the probability density function of the RUL for the purpose of computing the confidence interval. Adaptive capabilityThis is the crucial stage for real-world applications and is related to the model parameter tuning layer in Fig. 1 that connects the offline and online models. If an AI approach lacks adaptive flexibility, its use is limited.Power electronics have difficulties because the operational conditions of the training dataset, which is often acquired through accelerated testing trials, differ significantly from those of the in-situ system (i.e., the test data). Most of the research makes the assumption that the in-situ system's operational parameters are the same as those of the training dataset, which could not be the case in real-world applications.Therefore, the AI-based RUL prediction method's adaptability is essential for bridging the gap between research in academia and practical implementations in industry.Detailed mapping relationship derivations and transfer learning of degradation characteristics under different operating settings (temperature, voltage, humidity, etc.) are also interesting ways to tune model parameters. This means that system models need to be studied in great detail.Fig. 1 shows a methodical flowchart of power electronic system maintenance tasks. It typically comprises the three elements listed below.             Summarizing the Key PointsMaintenance of power electronic systems involves condition observation, anomaly identification, defect diagnosis, and remaining useful life prediction to ensure reliability and safety.The IEEE standard framework for prognostics and health management is applicable to power electronic systems, emphasizing the importance of a comprehensive maintenance approach.Data preprocessing and feature mining are crucial for improving the quality of raw data, enhancing the performance of prognostics and health management applications.AI-based remaining use life prediction techniques face challenges in real-world applications, requiring quantification of uncertainty and adaptability.Power electronic systems require an adaptive maintenance strategy to bridge the gap between research and practical implementation in industry, addressing operational parameter variations. ReferenceZhao, Shuai, Frede Blaabjerg, and Huai Wang. “An Overview of Artificial Intelligence Applications for Power Electronics.” IEEE Transactions on Power Electronics 36, no. 4 (April 2021): 4633–58. https://doi.org/10.1109/tpel.2020.3024914.

IntroductionThe potentiometer is a three-terminal resistive element whose resistances can be adjusted according to a certain change rule. According to it, it is used in a large variety of electrical and electronic circuits, such as voltage dividers, variable resistor, and current controllers. The potentiometer is usually composed of a resistor body and a movable brush. When the brush moves along the resistor body, the resistance value or voltage will be changed at the output end. Due to its special structure and function, it is necessary to pay attention to its damage and take regular maintenance during operation.Potentiometers - Basic IntroductionCatalogIntroductionⅠ Potentiometer Using TipsⅡ How to Clean Potentiometer?Ⅲ How to Test Potentiometer?3.1 General Methods3.2 Variable Potentiometer TestⅤ Replacing Potentiometer with 4 StepsⅠ Potentiometer Using Tips1) The resistor body of the potentiometer is mostly made of polycarbonate synthetic resin. Avoid contact with the following items: ammonia, other amines, aqueous alkali solutions, aromatic hydrocarbons, ketones, lipid hydrocarbons, and strong chemicals (excessive acid-base value), etc. Because chemical reaction with those will affect their performance.2) The terminal of the potentiometer should avoid using water-soluble flux when soldering, which will cause metal oxidation and mold material. In addition, avoid using inferior flux, and poor soldering may cause difficulty in soldering, resulting in poor contact or open circuit.3) If the soldering temperature is too high or the soldering time is too long, it may cause damage to the potentiometer terminals. The pin terminal should be soldered at 235℃±5℃ within 3 seconds, and the soldering space should be more than 1.5mm away from the potentiometer body. Do not use solder to hit through the circuit board when soldering, and wire terminal soldering should be soldered at 350℃±10℃ within 3 seconds. Except that, the terminal should avoid heavy pressure, otherwise it is easy to cause poor contact.4) During soldering, the height of the rosin (flux) entering the printing machine board should be adjusted properly, and the flux should be prevented from entering the potentiometer, otherwise it will cause poor contact between the brush and the resistor, resulting in INT, noise and other undesirable phenomena.Potentiometer Structure5) The potentiometer is best used in the voltage adjustment, and the connection method should choose "①" pin grounding. The current adjustment structure should be avoided, because the contact resistance between the resistor and the contact piece will stop the passage of large currents.6) Avoid condensation or water droplets on the surface of the potentiometer, and avoid using it in a humid place to prevent insulation deterioration or short circuit.7) When installing the rotary potentiometer, the strength should not be too tight to avoid damage to the screw teeth or poor rotation. When install the sliding type potentiometer, avoid using too long screws, otherwise it may affects the movement of the sliding handle, and even directly damages the potentiometer body.8) In the process of putting the potentiometer on the knob, the pushing force used should not be too large (not exceeding the parameter index of the pushing and pulling force of the shaft in the specification note), otherwise it may cause damage to the potentiometer.9) The operating force (rotation or sliding) of the potentiometer will become faster as the temperature rises, and slower as the temperature drops. If the potentiometer is used in a low temperature environment, it needs a kind of special low temperature resistant grease.10) The shaft or sliding handle of the potentiometer should be as short as possible when designing it. The shorter the shaft or sliding handle, the better and stable the hand feel. On the contrary, the longer the shaking, the greater the shaking, and the feel is easy to change.11) The power of the carbon film of the potentiometer can withstand the ambient temperature of 70°C, and its function may be lost when the temperature is higher than it.12) The resistor body of the sealed potentiometer is mostly made of polycarbonate synthetic resin. Avoid mixing with ammonia, aromatic hydrocarbons, lipid hydrocarbons, ketones, and strong chemicals (excessive pH), other amines, alkaline aqueous solution, etc, because they will affect its performance.Potentiometer TypesⅡ How to Clean Potentiometer?The potentiometer is to wrap the carbon sheet with POM, PC, ABS and other plastic materials. After assembly, the carbon sheet will not be exposed to the outside, it is not easy to oxidize, and dust is not easy to enter, which protects the potentiometer body.Cleaning Steps of Potentiometer1) Use a screwdriver to carefully open the sealing cover fixing card of the sealing potentiometer, and remove the protective cover.2) Remove the fixed spring card of the rotating shaft and pull out the rotating shaft.3) If some sealed potentiometers cannot take out the shaft, you can directly wipe the carbon film and the metal contacts on the shaft with a cotton ball dipped in pure alcohol.4) Adjust the position and angle of the metal contacts, changing the contact position with the carbon film and increasing the pressure.5) Apply some lubricating oil or special grease on the carbon film to delay the service life.6) Reinstall and fix the metal cover to complete the entire cleaning process. Ⅲ How to Test Potentiometer?3.1 General Methods1) Before detecting the potentiometer by the method of appearance and manual adjustment, firstly observe its appearance. Rotate the knob to check whether the rotation is smooth, whether the switch is flexible, whether the "click" sound is crisp when the switch is turned on and off, and listen to the sound of friction between the internal contact points of the potentiometer and the resistor body, if there is a loud noises indicate that the quality is not good. Normally, the handle should be slightly damped when turning.2) Using the multimeter to measure the potentiometer, you should first select the appropriate ohm gear of the multimeter according to the nominal resistance of the measured potentiometer and then do the measurement. When measuring, touch the red and black test leads of the multimeter to the pins of the fixed pins on both sides, and the multimeter reading should be the nominal resistance of the potentiometer. If the multimeter reading is much different from the nominal resistance value, it indicates that the potentiometer has been damaged.When the nominal resistance of the potentiometer is normal, then measure its changing resistance and whether the movable contact is in good contact with the resistor (fixed contact). At this time, one test lead of a multimeter is connected to the moving contact pin (usually the middle pin), and the other test lead is connected to a certain contact pin (pins on both sides).After connecting the test leads, the multimeter should display zero or the nominal resistance value, and then rotate the multimeter's shaft from one extreme position to the other extreme position, and the resistance value should continuously change from zero (or nominal resistance) to the nominal resistance value (or zero). During the rotation or sliding of the shaft of the potentiometer, if the pointer of the multimeter moves steadily or the displayed indication changes uniformly, it means that the measured potentiometer is in good condition. If the resistance reading of the multimeter fluctuates when the shaft is rotated, it means the movable contact has a fault with poor contact.3.2 Variable Potentiometer Test1) Measure the total resistance at both ends to see if it matches the nominal value.2) Measuring the resistance between a fixed end and the sliding end: rotary the potentiometer to see if the resistance change is continuous. Then measuring the resistances between the other fixed end and the sliding end, if the measured intermediate resistance value changes discontinuously, it indicates that there is a poor contact in the sliding process.PotentiometersⅣ Replacing Potentiometer with 4 StepsThere are many types of potentiometers, and most models cannot be used interchangeably, otherwise the control effect will not be very good. When replacing it, the nominal resistance value should be the same as the damaged variable resistance value or the close to. At the same time, its packages must be considered, otherwise the installation will be difficult. Therefore, we must distinguish between linear potentiometers, exponential potentiometers and logarithmic potentiometers before use. In addition, please note that the precision resistor can only be replaced with a same one when it is damaged, and cannot be replaced with an ordinary variable resistor, otherwise its adjustment accuracy will also be affected.The potentiometer has multiple pins. In order to prevent the wrong pins from being connected during replacement, the following specific operation steps and methods can be used:Step 1: Remove the set screw of the original potentiometer, but do not take off the leads on the potentiometer.Step 2: Install the new potentiometer and fix it.Step 3: Solder a lead on the original potentiometer pin slice, solder it on the corresponding pin slice of the new potentiometer, and the welding method is the same as the old one.Step 4: In the same way, solder each pin wire. Pay attention, welding the next one and then the other one can avoid the wrong position of the leads being welded to each other. Frequently Asked Questions about Potentiometer Uses and Its Replacement1. What is the use of potentiometer?The measuring instrument called a potentiometer is essentially a voltage divider used for measuring electric potential (voltage); the component is an implementation of the same principle, hence its name. Potentiometers are commonly used to control electrical devices such as volume controls on audio equipment. 2. What causes a potentiometer to fail?An electrical short or open will cause the indication to fail at one extreme or the other. If an increase or decrease in the potentiometer resistance occurs, erratic indicated valve position occurs. 3. What does a potentiometer measure?A potentiometer is an instrument which is used for measurement of potential difference across a known resistance or between two terminals of a circuit or network of known characteristics. A potentiometer is also used for comparing the emf of two cells. 4. How do you troubleshoot a potentiometer?Set your ohmmeter to a setting higher than the total resistance of the potentiometer. For example, if your potentiometer is rated at 1,000 ohms, set your ohmmeter to 10,000 ohms. Look at your potentiometer. There should be three tabs sticking out of it. 5. Does a potentiometer need to be grounded?This configuration also acts as a voltage divider and can be used in a number of ways to control a signal. Like any resistor, potentiometers per se do not need to be connected to the ground plane of the circuit, but in the majority of configurations/uses, they will be.