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There are various types of machinery and equipment, and as a result, different types of failures occur; different methods must be used to diagnose these various failures. I. Fault detection of vibration and noise: This is a type of fault that is common to most machines, and diagnosis is generally carried out using the following methods. 1. Vibration method: This involves measuring the vibration values of the key parts of a machine, such as displacement, velocity, acceleration, rotational speed, and phase values, and comparing them with standard values. Based on these measurements, it is possible to assess the operational condition of the machine on a macro level; this is the most commonly used method. 2. Feature analysis: Perform feature analysis on the aforementioned measured vibration quantities in the time domain, frequency domain, and time-frequency domain, in order to determine the nature and type of various faults in the machine. 3. Modal analysis and parameter identification method: Utilize the measured vibration parameters to identify the modal parameters of machine components, in order to determine the cause and location of the fault. 4. Impact energy and impact pulse measurement methods: Resonance demodulation technology (IFD) is used to detect faults in rolling bearings. 5. Acoustic method: Measuring machine noise allows one to understand the operating conditions of the machine and identify the sources of vibration. II. Fault detection of material cracks and defects: Material cracks include stress corrosion cracks and fatigue cracks, and the following methods can generally be used for their detection. 1. Ultrasonic testing: This method is cost-effective, capable of measuring large thicknesses, operates quickly, and is harmless to the human body; it is primarily used to detect planar defects. 2. Radiographic inspection: X-rays and Y-rays are primarily used in this method, which is mainly employed to detect volumetric defects. It is suitable for all types of materials, but the measurement cost is high and it can cause certain harm to the human body; therefore, caution is necessary when using it. 3. Penetrant testing methods mainly include fluorescent penetrant and colored penetrant testing. This method is simple to operate, low in cost, and has a wide range of applications; it provides intuitive visualization, but it is only suitable for damage types with surface defects. 4. Magnetic particle testing: This method is easy to use, more sensitive than penetrant testing, and capable of detecting defects near the surface; however, it is only applicable to ferromagnetic materials. 5. Eddy current testing: This method exhibits high sensitivity in detecting defects trapped beneath the surface of materials. It belongs to the category of electrical measurement techniques, and it is easy to automate and process using computers. 6. Laser holographic inspection method: This is a technology that was developed in the 1960s; it can be used to inspect various honeycomb structures, layered structures, high-pressure containers, and more. 7. Microwave detection technology: This is also a new technology that has been developed in recent decades. Its ability to penetrate non-metals is much greater than that of ultrasonic methods; it is characterized by speed and simplicity, and it represents a non-contact, non-destructive testing method. 8. Acoustic emission technology is primarily used to monitor and assess the integrity of large structural components. It enables dynamic, real-time monitoring of the growth of defects, and it features high sensitivity. Currently, it is widely applied in the detection of defects in pressure vessels, critical areas of nuclear power plants, as well as in situations involving leaks of radioactive materials and in the welding areas of pipelines. III. Detection of wear and corrosion faults in equipment components and materials: In addition to the ultrasonic testing method mentioned above among the non-destructive testing techniques, the following methods can also be employed for detecting such faults. 1. Fiber optic endoscopy: This technique uses specialized fiber optic endoscopes to directly observe surface wear and corrosion in materials. 2. Oil analysis technology: Oil analysis technology can be divided into two main categories; one is the analysis of the physical and chemical properties of the oil sample itself. IV. Fault detection caused by changes in temperature, pressure, and flow rate. Some faults in mechanical equipment systems are often reflected in changes in certain process parameters such as temperature, pressure, and flow rate. In addition to the conventional contact-type temperature measuring devices like thermal resistors and thermocouples installed on machines for temperature measurement, non-contact temperature measurement methods such as infrared thermometers and infrared thermal cameras are now used in some special applications. These devices measure based on the thermal radiation emitted by objects.