Basic structure   The essence of a programmable logic controller is a computer dedicated to industrial control. Its hardware structure is basically the same as that of a microcomputer. The basic structure is:   1. Power supply   The power supply of the programmable logic controller plays a very important role in the entire system. Without a good and reliable power supply system, it cannot work properly. Therefore, the manufacturer of the programmable logic controller also attaches great importance to the design and manufacture of the power supply. Generally, the AC voltage fluctuation is within the range of +10% (+15%), and the PLC can be directly connected to the AC power grid without taking other measures.   2. Central Processing Unit (CPU)   The central processing unit (CPU) is the control center of the programmable logic controller. It receives and stores the user program and data typed from the programmer according to the functions assigned by the programmable logic controller system program; checks the status of the power supply, memory, I/O and warning timer, and can diagnose syntax errors in the user program. When the programmable logic controller is put into operation, it first receives the status and data of each input device on site in a scanning manner, and stores them in the I/O image area respectively, and then reads the user program from the user program memory one by one, and after the command is interpreted, the results of the logical or arithmetic operation are sent to the I/O image area or data register according to the instructions. After all user programs are executed, the output status of the I/O image area or the data in the output register are finally transmitted to the corresponding output device, and the cycle runs until it stops.   In order to further improve the reliability of the PLC, large PLCs are also equipped with dual CPUs to form a redundant system, or a three-CPU voting system, so that even if a CPU fails, the entire system can still operate normally.   3. Memory   The memory that stores system software is called system program memory.   The memory that stores application software is called user program memory.   4. Input and output interface circuit   4.1. The field input interface circuit consists of an optical coupling circuit and a microcomputer input interface circuit, and serves as the input channel of the interface between the programmable logic controller and the field control.   4.2. The field output interface circuit is integrated with the output data register, the selection circuit and the interrupt request circuit, and the programmable logic controller outputs the corresponding control signal to the field execution component through the field output interface circuit.   5. Functional modules   Such as counting, positioning and other functional modules.   6. Communication module     PLC selection and case analysis   When selecting a PLC, you should analyze the characteristics of the process and the control requirements in detail, clarify the control tasks and scope, determine the required operations and actions, and then estimate the number of input and output points, required memory capacity, and determine the functions of the PLC and the characteristics of external devices based on the control requirements. Finally, select a PLC with a higher performance-price ratio and design a corresponding control system.   Below, we will detail the points that should be paid attention to when choosing PLC:   1. Estimation of Input and Output (I/O) Points Appropriate margin should be considered when estimating the number of I/O points. Usually, based on the statistical number of input and output points, an expandable margin of 10% to 20% is added as the estimated data for the number of input and output points.   2. Estimation of memory capacity; memory capacity is the size of the hardware storage unit that the programmable controller itself can provide, and program capacity is the size of the storage unit used by the user application project in the memory, so the program capacity is smaller than the memory capacity. In order to have a certain estimate of the program capacity during design and selection, the estimation of memory capacity is usually used as a substitute. Generally speaking, it is 10 to 15 times the number of digital I/O points, plus 100 times the number of analog I/O points, and this number is the total number of words in the memory (16 bits is one word), and another 25% of this number is considered as a margin. 3. Selection of control functions; this selection includes the selection of characteristics such as calculation function, control function, communication function, programming function, diagnostic function and processing speed.   (1) Operation function; the operation function of simple PLC includes logic operation, timing and counting function; the operation function of ordinary PLC also includes data shift, comparison and other operation functions; more complex operation functions include algebraic operation, data transmission, etc.; large PLC also has analog PID operation and other advanced operation functions. With the emergence of open systems, PLCs now have communication functions. Some products have communication with lower computers, some products have communication with the same computer or upper computer, and some products also have the function of data communication with the factory or enterprise network. When designing and selecting, we should start from the requirements of actual application and reasonably select the required operation functions. In most applications, only logical operation and timing and counting functions are needed. Some applications require data transmission and comparison. When used for analog detection and control, algebraic operation, numerical conversion and PID operation are used. Decoding and encoding operations are required to display data.   (2) Control functions: Control functions include PID control operations, feedforward compensation control operations, ratio control operations, etc., which should be determined according to control requirements. PLC is mainly used for sequential logic control. Therefore, single-loop or multi-loop controllers are often used in most cases to solve analog control. Sometimes, dedicated intelligent input and output units are also used to complete the required control functions, improve the processing speed of PLC and save memory capacity. For example, PID control units, high-speed counters, analog units with speed compensation, ASC code conversion units, etc. are used.   (3) Communication function: Large and medium-sized PLC systems should support a variety of fieldbuses and standard communication protocols (such as TCP/IP), and should be able to connect to the factory management network (TCP/IP) when necessary. The communication protocol should comply with ISO/IEEE communication standards and should be an open communication network. The communication interface of the PLC system should include serial and parallel communication interfaces (RS 232C/422A/485), RIO communication port, industrial Ethernet, common DCS interface, etc.; the main forms of the communication network of the PLC system are the following: 1) PC is the master station, and multiple PLCs of the same model are slave stations, forming a simple PLC network; 2) 1 PLC is the master station, and other PLCs of the same model are slave stations, forming a master-slave PLC network; 3) The PLC network is connected to a large DCS as a subnet of the DCS through a specific network interface; 4) Dedicated PLC network (dedicated PLC communication network of each manufacturer). In order to reduce the CPU communication task, according to the actual needs of the network composition, communication processors with different communication functions (such as point-to-point, fieldbus, industrial Ethernet) should be selected.   (4) Programming function; Offline programming mode: PLC and programmer share a CPU. When the programmer is in programming mode, the CPU only provides services for the programmer and does not control the field equipment. After programming is completed, the programmer switches to the running mode, and the CPU controls the field equipment and cannot be programmed. Offline programming can reduce system costs, but it is inconvenient to use and debug. Online programming mode: The CPU and programmer have their own CPUs. The host CPU is responsible for field control and exchanges data with the programmer within a scan cycle. The programmer sends the online compiled program or data to the host. In the next scan cycle, the host runs according to the newly received program. This method is more expensive, but the system debugging and operation are convenient, and it is often used in large and medium-sized PLCs.   (5) Diagnostic function The diagnostic function of PLC includes hardware and software diagnosis. Hardware diagnosis determines the fault location of hardware through hardware logic judgment, and software diagnosis is divided into internal diagnosis and external diagnosis. Diagnosis of the internal performance and function of PLC through software is internal diagnosis, and diagnosis of the information exchange function between PLC CPU and external input and output components through software is external diagnosis. The strength of the PLC's diagnostic function directly affects the technical capabilities required of operators and maintenance personnel, and affects the average repair time.   (6) Processing speed PLC works in scanning mode. From the perspective of real-time requirements, the processing speed should be as fast as possible. If the signal duration is less than the scanning time, the PLC will not be able to scan the signal, resulting in the loss of signal data. The processing speed is related to the length of the user program, the CPU processing speed, the software quality, etc. At present, the PLC contacts have fast response and high speed. The execution time of each binary instruction is about 0.2 to 0.4Ls, so it can adapt to the application needs with high control requirements and fast response requirements. The scanning cycle (processor scanning cycle) should meet the following requirements: the scanning time of small PLC is not more than 0.5ms/K; the scanning time of large and medium-sized PLC is not more than 0.2ms/K.   4. Model selection   （1） Types of PLC PLC is divided into two categories according to structure: integral type and modular type. It is divided into two categories according to application environment: field installation and control room installation. It is divided into 1 bit, 4 bit, 8 bit, 16 bit, 32 bit, 64 bit, etc. according to CPU word length. From the application point of view, it can usually be selected according to control function or input and output points. The I/O points of integral PLC are fixed, so users have less room for choice and are used in small control systems; modular PLC provides a variety of I/O cards or plug-in cards, so users can reasonably select and configure the I/O points of the control system. Function expansion is convenient and flexible, and it is generally used in large and medium-sized control systems.   (2) Selection of input and output modules; the selection of input and output modules should be consistent with application requirements. For example, for input modules, application requirements such as signal level, signal transmission distance, signal isolation, and signal power supply method should be considered. For output modules, the type of output module to be selected should be considered. Generally, relay output modules have the characteristics of low price, wide voltage range, short life, and long response time; thyristor output modules are suitable for frequent switching and inductive low power factor load occasions, but they are more expensive and have poor overload capacity. Output modules also have DC output, AC output, and analog output, which should be consistent with application requirements. According to application requirements, intelligent input and output modules can be reasonably selected to improve the control level and reduce application costs. Consider whether an expansion rack or remote I/O rack is needed.   (3) Power supply selection The power supply of PLC, in addition to the design and selection of PLC according to the requirements of the product manual when introducing equipment, the power supply of PLC should be designed and selected according to the requirements of the product manual. In general, the power supply of PLC should be designed and selected with 220VAC power supply, which is consistent with the voltage of the domestic power grid. For important applications, an uninterruptible power supply or a voltage-stabilized power supply should be used. If the PLC itself has a usable power supply, it should be checked whether the current provided meets the application requirements, otherwise an external power supply should be designed. In order to prevent the external high-voltage power supply from being introduced into the PLC due to misoperation, it is necessary to isolate the input and output signals, and sometimes a simple diode or fuse tube can be used for isolation.   (4) Memory selection: Due to the development of computer integrated chip technology, the price of memory has dropped. Therefore, in order to ensure the normal operation of the application project, the PLC memory capacity is generally required to be at least 8K memory according to 256 I/O points. When complex control functions are required, a larger capacity and higher grade memory should be selected.   (5) Economic Considerations When choosing a PLC, you should consider the performance-price ratio. When considering economic efficiency, you should also consider factors such as the scalability, operability, and input-output ratio of the application, make comparisons and take them into account, and finally select a more satisfactory product. The number of input and output points has a direct impact on the price. Each additional input and output card will increase the cost. When the number of points increases to a certain value, the corresponding memory capacity, rack, motherboard, etc. will also increase accordingly. Therefore, the increase in the number of points has an impact on the selection of CPU, memory capacity, control function range, etc. It should be fully considered during the estimation and selection to make the entire control system have a more reasonable performance-price ratio.  

In the long-term maintenance of Rockwell AB's PLC controller, some knowledge about AB's PLC controller and some practical and effective troubleshooting methods for its common faults in actual production are summarized.   The hardware series of Rockwell AB's PLC include PLC5, ControlLogix, SLC500, MicroLogix, etc.; the commonly used communication software include RSLinx, etc.; the monitoring interface software include Intouch, RSView32, etc.; the programming software include RSLogix5, RSLogix500, RSLogix5000. Now we will give a brief introduction to the AB PLC controller used in our factory and the troubleshooting methods of common faults .   Controllogix   SLC 500 Series PLC (Medium-sized Control System) RSLinx software is a copy of RSLogix software. When performing CPU communication on RSLogix, you must first run RSLinx Lite, which is the interface software used for communication.   The module of SLC500 is generally 1746-×××, the CPU is 1747, and its addressing mode is the selection of slots. The power modules are generally 1746-P1, P2, P3, P4, of which only P3 is 24V DC and the rest are 220V AC input. The CPU of PLC5 is 1785-L20, L30..., which can connect up to four remote I/O channels and up to 32 remote I/O nodes (number of physical devices). The power module is 1771-P7. The addressing modes of PLC5 include 2-slot addressing, 1-slot addressing, and 1/2-slot addressing. 2-slot addressing means that each physical 2-slot I/O group corresponds to 1 word (16 bits) in the input/output image table. 1-slot addressing means that 1 physical slot corresponds to 1 word (16 bits) in the input/output image table. 1/2-slot addressing means that 1 physical slot corresponds to 2 words (32 bits) in the input/output image table.   Both types of CPUs have key switches that can be switched between RUN, PROG, and REM. RUN stands for operation, PROG stands for programming, and REM is between the two and can be defined by software as RUN or PROG. If it switches from RUN to REM, it is RUN, and if it switches from PROG to REM, it is PROG. The lights on the CPU of SLC500 include RUN, FLT, BATT, DH+, FORCE, and RS232. When they are on, they represent normal, fault, low battery, normal DH+ communication, forced output, and serial communication. When the light BATT on the CPU of PLC5 is on, it means that the battery voltage is low; PROC is green for operation and red for fault; FORC is on when it means that forced I/O is valid; CO is on when it is normal. The communication between them, including the remote adapter card, uses the DH+ communication link. The host computer communicates with the CPU by running the RSLinx Lite or RSLinx Gatewey software on the computer. Local programming can use RS-232 or DH+ communication links, and remote programming can use DH+ or Ethernet.   The programs in AB's PLC5 and SLC500 are generally not easily lost, so the faults are generally manifested as communication faults and module faults. The performance of AB's PLC hardware is relatively stable, so the dry ice line PLC has few faults. The common ones are generally the following:   1. The analog input quantity is displayed as a certain value and will not change. One situation occurs before starting up. In this case, first check whether the red light of the analog input module is on. If it is on, turn off the power and swap the modules to check whether the module is burned out. If it is broken, replace it. If it is not broken or the light is not on, it is a data transmission failure or a scanning failure. In this case, it can usually be restored by re-powering the PLC. The other situation occurs during operation. This situation is generally caused by a CPU module and analog module failure. Sometimes it can be restored by re-powering on. If it cannot be restored, it may be that the CPU module is broken.   2. The operation command is not executed, that is, the operation does not work. There are generally two possibilities for this situation. One is that the conditions that the operation should have are not met, so the operation does not work. The other is that the program is in its own closed loop, that is, an infinite loop or the scan time overflows, etc., causing output prohibition, or communication failure. In this case, you can stop the system first and then restart it, or turn off the power of the system and then turn it to automatic and start it to recover. If it cannot be recovered, re-powering the PLC can generally recover it.   3. All the outputs of the PLC are not working, that is, the indicator lights on the modules corresponding to the output points are not on. There are only one possible reason for this failure, that is, the 24V power supply provided by the output module is gone, one is that the intermediate relay that provides power to the output module is not in the condition of being attracted, and the other is that the coil of the intermediate relay is burned out or the contact is poor.   4. The signal is not received for a long time, causing a control unit to be unable to operate. This situation is a communication failure or data transmission failure, which can usually be restored by redoing the steps that generated the signal.   5. The green lights of all the input and output modules of the PLC are off. In this case, first check whether there is 220V AC at the input of the power module. If not, check the quality of the power supply transformer. If yes, the power module is broken.   6. During operation, the online device suddenly stops working, that is, the PLC suddenly "freezes". In this case, first check the status of the PLC. If the lights on all modules are off, it is very likely that the PLC power module is broken; if the lights on all modules are on when you press the CPU with your finger, then cut off the power, unplug the CPU and plug it in again. Generally, the fault can be eliminated. Another situation is that the input and output points of some input and output modules are not displayed. In this case, when eliminating the input and output module fault, unplugging and plugging the CPU can generally eliminate the fault.   7. If the DH+ or COM light on the CPU flashes or turns red, it means a communication fault. One case is that the DH+ cable is broken or the socket is loose. Check and fix the DH+ cable and socket until the fault disappears. Another case is that the communication address of the CPU is wrong or has been changed. In this case, you must enter RSLinx and click the communication configuration icon to reconfigure the address of the upper computer or PLC icon with a red cross until the red cross disappears.   8. The FLT fault light on the CPU flashes and the key cannot be reset. If the problem cannot be solved by checking the battery and modules, reconfigure the hardware download program.   In short, in the actual production process, we will encounter various PLC failures. Although the hardware performance of AB's PLC is relatively stable and the possibility of failure is very small, for us electrical maintenance personnel, whether it is AB's PLC or Siemens' PLC, as long as we use it, we must master it. Our knowledge of PLC programmable controller software and hardware is always lagging behind. Only by continuous learning and mastering some PLC maintenance methods and troubleshooting methods can PLC serve us better.  

What is a frequency converter   According to the definition of "GB/T 2900.1-2008 Basic Terms of Electrical Engineering": Frequency converter refers to an electric energy converter that changes the frequency related to electric energy.   Simple frequency converters can only adjust the speed of AC motors. It can be open-loop or closed-loop depending on the control method and frequency converter. This is the traditional V/F control method. Now many frequency converters have established mathematical models to convert the stator magnetic field UVW3 phases of AC motors into two current components that can control the motor speed and torque. Now most famous brands of frequency converters that can perform torque control use this method to control torque. The output of each phase of UVW must be added with a molar effect current detection device. After sampling and feedback, the PID adjustment of the current loop with closed-loop negative feedback is formed; ABB's frequency converter has proposed a direct torque control technology that is different from this method. Please refer to relevant information for details. In this way, both the speed and torque of the motor can be controlled, and the speed control accuracy is better than v/f control. Encoder feedback can be added or not. When it is added, the control accuracy and response characteristics are much better.   What is a servo   Driver: Based on the development of frequency conversion technology, the servo driver has implemented more precise control technology and algorithmic operations in the current loop, speed loop and position loop (the frequency converter does not have this loop) inside the driver than in general frequency conversion. It is also much more powerful than traditional servos in terms of functions. The main point is that it can perform precise position control. The speed and position are controlled by the pulse sequence sent by the upper controller (of course, some servos have integrated control units or directly set parameters such as position and speed in the driver through bus communication). The internal algorithm of the driver, faster and more accurate calculations, and better-performing electronic devices make it superior to the frequency converter.   Motor: The material, structure and processing technology of servo motors are much better than those of AC motors driven by inverters (general AC motors or various types of variable frequency motors such as constant torque and constant power). That is to say, when the driver outputs a power supply with rapidly changing current, voltage and frequency, the servo motor can produce corresponding action changes according to the power supply changes. The response characteristics and overload resistance are much better than those of AC motors driven by inverters. The serious difference in motors is also the fundamental reason for the difference in performance between the two. That is to say, it is not that the inverter cannot output a power signal that changes so quickly, but that the motor itself cannot respond. Therefore, when the internal algorithm of the inverter is set, a corresponding overload setting is made to protect the motor. Of course, even if the inverter output capacity is not set, it is still limited. Some inverters with excellent performance can directly drive servo motors!   An important difference between servo and frequency conversion   Frequency conversion can be done without encoders, but servos must have encoders for electronic commutation. The technology of AC servo itself is based on and applies frequency conversion technology. It is achieved by imitating the control method of DC motors through frequency conversion PWM on the basis of DC motor servo control. In other words, AC servo motors must have frequency conversion: frequency conversion is to rectify the 50, 60HZ AC power into DC power first, and then invert it into a frequency-adjustable waveform similar to sine and cosine pulsating power through various transistors with controllable gates (IGBT, IGCT, etc.) through carrier frequency and PWM regulation. Since the frequency is adjustable, the speed of the AC motor can be adjusted (n=60f/2p, n speed, f frequency, p pole pair number).

1. Classification of harmonic interference problems in servo drive systems The harmonic interference problems faced by the servo drive system can be divided into three categories according to the interference source and the disturbed source, namely, external harmonic interference to the servo drive system, servo drive system harmonic interference to the internal components of the servo drive system, and servo drive system interference to the outside world:   ⑴ External harmonics interfere with the servo drive system External harmonics mainly include: harmonics in the power supply, harmonics in nature (harmonics caused by lightning, etc.). These harmonics can cause a series of problems such as false alarms, false operations, and refusal to operate of the servo drive in the servo drive system. In more serious cases, the rectifier module and electrolytic capacitor in the servo drive may overheat, burst, explode, and other problems. Therefore, this part of the harmonics must be taken seriously.   ⑵ The servo drive system interferes with the internal components of the servo drive system This is a common situation. For example, the harmonics generated by the servo drive in the servo drive system can enter the servo motor, causing the servo motor to overheat, make noise (screaming, abnormal sound, etc.), vibrate (or oscillate), have pits, pits and cracks on the bearings, frequently break down the servo motor insulation, and severely shorten the life of the servo motor. Of course, the harmonics in the servo drive system will not only affect the servo motor, but may also affect a series of problems such as communication and analog signals.   ⑶ Servo drive system harmonic interference to the outside world There are two situations in which the servo drive system interferes with the outside world. One is that the harmonic interference of the servo drive system interferes with the electrical equipment that uses the same power supply, such as low voltage, instruments, meters, sensors, etc.; the other is that the harmonics of the servo drive system will radiate outward, causing the surrounding equipment to not work properly, such as communications, monitoring, instruments, meters, sensors, etc.   2. Solutions for reference to harmonic interference in servo drive systems When it comes to the harmonic interference problem of the servo drive system, first of all, don't blindly rush to install any servo harmonic suppression devices. This will not only increase costs and space occupancy, but also increase failure points. Therefore, this is not the preferred solution .   ⑴ Grounding Do a good job of grounding the servo drive system. The grounding of the servo drive system must be independent and distinguished from the grounding of other equipment; the grounding wire must be short and thick, and the wire diameter of the grounding wire must be at least half of the main wire diameter or more. We recommend that the grounding wire and the main wire of the servo drive system use the same wire diameter;   ⑵ Shielding It is recommended to use shielded wires for the connection wires between the servo drive system and the servo motor, and cut the shielding layer in a circular manner to expose the metal mesh, and then use a U-shaped clip or the like to ground it. For weak-wires such as communication lines and signal lines of the servo drive system, shielded wires should be used as much as possible, and the shielding layer should be reliably grounded;   ⑶ Filtering The filter components available for servo drive systems include: servo input filter, servo input inductor, MLAD-GFC servo-specific passive harmonic filter, servo-specific active harmonic filter, Du/Dt inductor, sine wave inductor, etc.  

The Integration of the 2024 Paris Olympics with Industrial Automation   In 2024, France's Paris will host the highly anticipated global sporting event—the Summer Olympics. This is not only a grand celebration of athletic competition but also a showcase of technology and innovation. In this edition of the Olympics, the application of industrial automation technologies will provide robust support for the smooth running of the events, enhance the audience experience, and optimize resource management.   The Importance of Industrial Automation in the Olympics Industrial automation technology plays a crucial role in organizing and managing large-scale events in modern times. Through automated systems, efficient management of various aspects such as venues, transportation, and security can be achieved. For instance, automated warehousing systems can assist event organizers in effectively managing materials, ensuring that necessary equipment and supplies reach different venues on time.   Specific Application Cases 1.Intelligent Traffic Management During the Paris Olympics, a significant influx of spectators, athletes, and staff is expected in the city. To meet this challenge, Paris will utilize intelligent traffic solutions provided by Siemens. These systems monitor and adjust traffic flow through real-time data analysis and predictive algorithms, ensuring smooth traffic during the events.   2.Automated Security Systems Safety is paramount at large-scale events. Companies like Yaskawa and Honeywell will provide advanced security automation systems for the Olympics. These systems combine video surveillance, facial recognition technology, and drone monitoring to continuously oversee safety conditions inside and outside the venues, quickly identifying and addressing potential security threats.   3.Smart Venue Management In the area of venue management, Schneider Electric will provide smart building management systems. These systems can monitor energy consumption, temperature, and air quality in real-time to ensure optimal conditions in the venues throughout the different events. Additionally, automated controls can effectively reduce energy consumption, aligning with sustainability goals.   4.Robot Services With the advancement of robotics technology, robots will offer a variety of services during the events. Boston Dynamics will showcase its advanced service robots, which will guide spectators, provide information, and transport items within the venues, thereby enhancing the audience experience.   Conclusion The 2024 Paris Olympics is not only a stage for athletes to showcase their talents but also a proving ground for the application of industrial automation technologies. By introducing advanced automation solutions, Paris will present a safe, efficient, and intelligent Olympic experience to global audiences. The application of these technologies not only enhances event organization efficiency but also offers new ideas and directions for managing future large-scale events. With continuous technological advancements, we can believe that future Olympic Games will be even more intelligent and automated.

PLC, or programmable logic controller, is an electronic device widely used in the field of industrial control. As a high-performance control device, PLC can be used in many fields such as automated production control, process control, logistics control, and data processing.   1）. Definition of PLC   PLC is an electronic device used for industrial control, which contains multiple functional components such as CPU, memory, input and output ports, communication interface, etc. It controls through programs to realize the automatic control of various industrial equipment and machines. PLC first appeared in the 1960s, and since then, PLC has played an irreplaceable role in the field of industrial automation.     2）. Characteristics of PLC   1. Programmability: PLC contains a variety of functional components, which can control and adjust the control process by writing programs, and can adapt to complex industrial control processes and production needs.   2. Stability: PLC has the characteristics of high stability and strong reliability, and can operate stably for a long time in complex and harsh industrial environments.   3. Scalability: PLC can add expansion boards according to production needs, thereby realizing the functional expansion of industrial production lines.   4. Easy to maintain: The modular design of PLC makes it easy to maintain, and faulty modules can be replaced quickly.     3）. Advantages of PLC   1. Stable and reliable: PLC adopts high-quality electronic components and modular design, and can operate stably and reliably in complex industrial environments.   2. Efficient automatic control: PLC can realize automatic control of the control process by writing programs, reduce manual intervention and improve production efficiency.   3. Easy to maintain: The modular design of PLC makes it easy to maintain, and faulty modules can be quickly replaced, reducing downtime and repair costs.   4. High flexibility: The programmability of PLC enables it to flexibly adapt to different production needs, enhancing its scope of application.     4）. Application of PLC   PLC is widely used in many fields such as automated production control, process control, logistics control and data processing. The following are some typical application examples:   1. Automated production control: PLC can be used for fully automated control of production lines, such as automatic assembly, automated sorting, and automated packaging.   For example, in a company's production line, it is necessary to automatically control the speed and position of goods on the conveyor belt to achieve fast and efficient logistics operations. The company installed a PLC control system and realized precise control of the speed, position and other parameters of the conveyor belt by writing programs, which greatly improved the efficiency and accuracy of logistics operations.     2. Process control: PLC can be used for automated control of various industrial processes, including water treatment, chemical manufacturing, food processing and pharmaceuticals.   For example, a water treatment plant needs to precisely control the flow of water. The plant uses a PLC control system and writes programs to achieve real-time monitoring and automatic control of water flow, water quality and other parameters, thereby ensuring that the water quality and flow are within a reasonable range and improving the efficiency and quality of water treatment.   3. Logistics control: PLC can be used for the automated control of various logistics equipment, including logistics sorting, cargo transportation, and automated storage.   For example, the truck loading and unloading platform needs to accurately control the unloading speed and position of the items. The truck loading and unloading platform adopts PLC control system, which can realize accurate control of the goods by writing programs, greatly improving the unloading efficiency and safety of the goods.     In short, PLC is a high-performance control system with advantages such as high stability and strong reliability. PLC is widely used in automated production control, process control, logistics control and data processing. Through PLC automated control, production efficiency can be improved, manual intervention can be reduced, product quality can be improved, and enterprises can be helped to reduce costs and improve market competitiveness.  

1 Grounding Problems   The grounding requirements for the PLC system are relatively strict. It is best to have an independent dedicated grounding system. Also, attention should be paid to the reliable grounding of other equipment related to the PLC.   When multiple circuit ground points are connected together, unexpected currents can flow, causing logic errors or damaging circuits.   The reason for different ground potentials is usually that the grounding points are separated too far in physical area. When devices that are far apart are connected by communication cables or sensors, the current between the cable and the ground will flow through the entire circuit. Even within a short distance, the load current of large equipment can change between its potential and the ground potential, or directly generate unpredictable currents through electromagnetic effects.     Between power supplies with improper grounding points, destructive currents may flow in the circuit, destroying equipment.   PLC systems generally use a single-point grounding method. In order to improve the ability to resist common-mode interference, shielded floating ground technology can be used for analog signals, that is, the shielding layer of the signal cable is grounded at one point, the signal loop is floating, and the insulation resistance with the ground should be no less than 50MΩ.     2 Interference handling     The industrial field environment is relatively harsh, with many high and low frequency interferences. These interferences are usually introduced into the PLC through the cables connected to the field equipment.     In addition to grounding measures, some anti-interference measures should be taken during the design, selection and installation of cables:   (1) Analog signals are small signals and are easily affected by external interference, so double-shielded cables should be used;   (2) Shielded cables should be used for high-speed pulse signals (such as pulse sensors, counting encoders, etc.) to prevent external interference and high-speed pulse signals from interfering with low-level signals;   (3) The communication cable between PLCs has a high frequency. Generally, the cable provided by the manufacturer should be selected. If the requirements are not high, a shielded twisted pair cable can be selected.   (4) Analog signal lines and DC signal lines cannot be routed in the same wire duct as AC signal lines;   (5) The shielded cables leading into and out of the control cabinet must be grounded and should not be directly connected to the equipment through the wiring terminals;   (6) AC signals, DC signals and analog signals cannot share the same cable, and power cables should be laid separately from signal cables.   (7) During on-site maintenance, the following methods can be used to resolve interference: using shielded cables for the affected lines and re-laying them; adding anti-interference filtering codes to the program.     3 Eliminate inter-wire capacitance to avoid false operation     There is capacitance between each conductor of the cable, and a qualified cable can limit this capacitance within a certain range.   Even if the cable is qualified, when the cable length exceeds a certain length, the capacitance between the lines will exceed the required value. When this cable is used for PLC input, the capacitance between the lines may cause the PLC to malfunction, resulting in many incomprehensible phenomena.   These phenomena are mainly manifested as: the wiring is correct, but there is no input to the PLC; the input that the PLC should have is not there, but the input that it should not have is there, that is, the PLC inputs interfere with each other. To solve this problem, you should do the following:     (1) Use cables with twisted cores;   (2) Try to shorten the length of the cable used;   (3) Use separate cables for inputs that interfere with each other;   (4) Use shielded cable.     4 Output module selection     Output modules are divided into transistor, bidirectional thyristor, and contact type:   (1) The transistor type has the fastest switching speed (generally 0.2ms), but the smallest load capacity, about 0.2~0.3A, 24VDC. It is suitable for equipment with fast switching and signal connection. It is generally connected to signals such as frequency conversion and DC devices. Attention should be paid to the impact of transistor leakage current on the load.   (2) The advantages of the thyristor type are that it has no contacts, has AC load characteristics, and has a small load capacity.   (3) Relay output has AC and DC load characteristics and large load capacity. In conventional control, relay contact type output is generally used first. The disadvantage is that the switching speed is slow, generally around 10ms, and it is not suitable for high-frequency switching applications.     5 Inverter overvoltage and overcurrent processing   (1) When the given speed is reduced to slow down the motor, the motor enters the regenerative braking state, and the energy fed back to the inverter by the motor is also high. This energy is stored in the filter capacitor, causing the voltage on the capacitor to increase and quickly reach the setting value of the DC overvoltage protection, causing the inverter to trip.   The solution is to add a braking resistor outside the inverter and use the resistor to consume the regenerative electric energy fed back to the DC side by the motor.   (2) The inverter is connected to multiple small motors. When an overcurrent fault occurs in one of the small motors, the inverter will issue an overcurrent fault alarm, causing the inverter to trip, thereby causing other normal small motors to stop working.   Solution: Install a 1:1 isolation transformer on the output side of the inverter. When one or more small motors have an overcurrent fault, the fault current will directly impact the transformer instead of the inverter, thus preventing the inverter from tripping. After the experiment, it works well and the previous fault of normal motors stopping has not occurred.     6 Inputs and outputs are labeled for easy maintenance   PLC controls a complex system. All you can see are two rows of staggered input and output relay terminals, corresponding indicator lights and PLC numbers, just like an integrated circuit with dozens of pins. Anyone who does not look at the schematic diagram to repair a faulty device will be helpless and the speed of finding the fault will be very slow. In view of this situation, we draw a table based on the electrical schematic diagram and stick it on the console or control cabinet of the equipment, indicating the electrical symbol and Chinese name corresponding to each PLC input and output terminal number, which is similar to the functional description of each pin of the integrated circuit.   With this input and output table, electricians who understand the operation process or are familiar with the ladder diagram of this equipment can start maintenance.   However, for those electricians who are not familiar with the operation process and cannot read ladder diagrams, they need to draw another table: PLC input and output logic function table. This table actually explains the logical correspondence between the input circuit (trigger element, associated element) and the output circuit (actuator) in most operation processes.   Practice has proved that if you can skillfully use the input-output correspondence table and the input-output logic function table, you can easily repair electrical faults without drawings.     7 Inferring Faults through Program Logic   There are many types of PLCs commonly used in industry today. For low-end PLCs, the ladder diagram instructions are similar. For mid- to high-end machines, such as S7-300, many programs are written using language tables.   Practical ladder diagrams must have Chinese symbol annotations, otherwise it will be difficult to read. If you can have a general understanding of the equipment process or operation process before reading the ladder diagram, it will seem easier.   If an electrical fault analysis is to be performed, the reverse search method or reverse reasoning method is generally used, that is, according to the input-output correspondence table, the corresponding PLC output relay is found from the fault point, and then the logical relationship that satisfies its action is reversed.   Experience shows that if one problem is found, the fault can be basically eliminated, because it is rare for two or more fault points to occur simultaneously in the equipment.     8 PLC self-fault judgment   Generally speaking, PLC is an extremely reliable device with a very low failure rate. The probability of damage to hardware such as PLC and CPU or software errors is almost zero. The PLC input point will hardly be damaged unless it is caused by strong electric intrusion. The normally open point of the PLC output relay will have a long contact life unless the peripheral load is short-circuited or the design is unreasonable, and the load current exceeds the rated range.   Therefore, when we look for electrical fault points, we should focus on the PLC's peripheral electrical components and not always suspect that there is a problem with the PLC hardware or program. This is very important for quickly repairing faulty equipment and resuming production.   Therefore, the electrical fault inspection and repair of the PLC control circuit discussed by the author does not focus on the PLC itself, but on the peripheral electrical components in the circuit controlled by the PLC.     9 Make full and reasonable use of software and hardware resources   (1) Instructions that do not participate in the control cycle or have been entered before the cycle do not need to be connected to the PLC;   (2) When multiple instructions control a task, they can be connected in parallel outside the PLC and then connected to an input point;   (3) Make full use of the PLC internal functional soft components and fully call the intermediate state to make the program complete and coherent and easy to develop. At the same time, it also reduces hardware investment and reduces costs;   (4) If conditions permit, it is best to make each output independent, which is convenient for control and inspection and also protects other output circuits; when an output point fails, it will only cause the corresponding output circuit to lose control;   (5) If the output is a forward/reverse controlled load, not only must the PLC internal program be interlocked, but measures must also be taken outside the PLC to prevent the load from moving in both directions;   (6) PLC emergency stop should be cut off using an external switch to ensure safety.     10 Other considerations   (1) Do not connect the AC power cord to the input terminal to avoid burning the PLC;   (2) The grounding terminal should be grounded independently and not connected in series with the grounding terminal of other equipment. The cross-sectional area of the grounding wire should not be less than 2mm²;   (3) The auxiliary power supply is small and can only drive low-power devices (photoelectric sensors, etc.);   (4) Some PLCs have a certain number of occupied points (i.e. empty address terminals), do not connect the wires;   (5) When there is no protection in the PLC output circuit, a protective device such as a fuse should be connected in series in the external circuit to prevent damage caused by load short circuit.

    Common Motor Failures   1.Abnormal startup or abnormal speed after startup 1）Stator circuit (power supply, switch, contactor, leads, windings) missing phase. 2）Rotor cage breakage (ring breakage, bar breakage). 3）Rotor rubbing against stator, or mechanical drag causing jamming. 4）Incorrect stator circuit wiring (winding polarity or star/delta configuration). 5）Low power supply voltage.   2.Overheating or smoking 1）Power aspect High or low voltage, or phase loss. 2）Motor itself Stator winding inter-turn or turn-to-turn short circuit or ground, rotor bar breakage or stator/rotor rubbing. 3）Load aspect Mechanical overload or jamming. 4）Ventilation and heat dissipation aspect High ambient temperature, excessive dirt on casing, blocked air ducts, damaged or improperly installed fan.   3.Bearing operating temperature is too high 1）High bearing running temperature Bearing running temperature should generally not exceed 95°C. 2）Improper, deteriorated, excessive, or inadequate lubricating oil. 3）Bearing wear, rust, spalling, inner or outer race running, or improper assembly of inner and outer covers. 4）Misalignment of couplings or over-tightened belts.   4.Abnormal noise or strong vibration 1）Stator-rotor rubbing or severe wear deformation of driven machinery. 2）Uneven foundation, weak base, or loose anchor bolts. 3）Coupling misalignment or bent shaft. 4）Rotor eccentricity, rotor imbalance, unbalanced driven machinery, or bearing eccentricity. 5）Oil shortage or damage to bearings. 6）Rotor bar breakage. 7）Phase loss or overloaded operation.     Motor Inspection   1.Pre-operation inspection 1）Check if the casing is clean, inspect for dust and dirt inside open motors. 2）Disconnect cables and terminal boards, measure winding resistance and insulation to ground. 3）Verify correct stator winding connection and power supply voltage as per nameplate. 4）Manually rotate motor rotor and drive system, check for obstructions and bearing lubrication. 5）Ensure ventilation system is unobstructed, and all fasteners are secure. 6）Check grounding of motor.   2.Operational inspection 1）During normal operation, current and voltage should not exceed rated values. Phase current imbalance should not exceed 10%, phase voltage imbalance should not exceed 5%, and allowable voltage fluctuation is within -5% to +5% of rated voltage, not to exceed 10%. 2）Ensure temperature measurement devices are working, temperature rise within specified range. 3）Normal sound and vibration, no abnormal odors. 4）Proper bearing lubrication, flexible rotation of oil ring. 5）Cooling system in good condition. 6）Clean surroundings without debris, leaks of water, oil, or air. 7）Protective covers, terminal boxes, grounding wires, control boxes intact.    Motor Maintenance   1）Keep motor surroundings clean and free of debris. 2）Regular inspection, address anomalies, record defects. 3）Prevent water or steam leaks around, avoiding motor dampness affecting insulation. 4）Regularly change lubricating oil, typically every 1000 hours for plain bearings, and 500 hours for roller bearings. 5）Periodically inspect insulation of standby motors, address non-compliance promptly.

（1）. Manual Control Method The Yaskawa drive can achieve manual control of motor rotation through the control panel. The specific method is as follows: 1. Open the control panel and enter manual mode. 2. Set the frequency to 0Hz first, then press the start button, the motor will stop at this time. 3. Press the forward or reverse button, the motor will rotate in the set direction. 4. The motor speed can be adjusted by setting the frequency. Note: When manually controlling the motor rotation, one should keep a clear mind to ensure their safety.   （2）. Precautions 1. Before performing manual control, ensure that the equipment has been correctly electrically connected and mechanically installed. 2. Understand the basic operation methods of the equipment first and then manually control it ensuring safety. 3. When manually adjusting the motor speed, gradually increase or decrease the frequency to avoid frequent changes causing overload and affecting the equipment's lifespan. 4. After manual operation, thoroughly stop the motor rotation, and turn off the control panel to avoid safety hazards.   （3）. Common Issues 1. The motor may not rotate steadily during manual control, which could be due to incorrect electrical connections or excessive motor load. 2. Noise and unusual smells during manual control may indicate mechanical faults in the equipment. 3. If the control panel fails to start or adjust the frequency after starting, it could be due to a malfunction in the control panel itself. 4. If the above problems cannot be resolved, promptly contact equipment maintenance technicians for assistance.   In conclusion, Yaskawa drive is a high-precision driving device, and the correct manual control method is crucial for enhancing equipment operation efficiency and ensuring the safety of operators.

The PLC-5 controller is in the central position of the control system, integrates the existing and future systems through ethernet/ip, ControlNet and DeviceNet, and provides the interconnection between SLC 500, ControlLogix and Micrologix processors. Because the PLC-5 processor has built-in network connection, PLC-5 makes the control structure flexible enough to establish economic connection between a wide range of equipment.       The minimum configuration of a PLC-5/1771 control system includes a programmable controller module and some input and output modules and power supply modules installed on a rack. The controller with communication port can be selected as required. PLC-5 can reach 512 input and output points at most. All PLC-5 processors have remote I / O interfaces. Some PLC-5 processors have local extended I / O interfaces. Some PLC-5 processors have local extended I / O interfaces. Some PLC-5 processors have a ControlNet communication interface. If you want to provide a DeviceNet I / O scanner port for the system, you must add a DeviceNet scanner module (1771-SDN).       PLC-5 is a large, stable and early product of Rockwell Automation   Worldwide, more than 450000 sets of PLC-5 and more than 10000000 PLC-5 1771 i/o modules are operating stably.   PLC-5 has a module MTBF index of more than 400000 hours.   PLC-5 hot standby system can be used for occasions with high control safety requirements.       In recent years, PLC-5 has added ControlNet, DeviceNet, ethernet/ip and other industrial network interface functions.       PLC-5 controllers can be divided into the following categories:       1. Classic PLC-5 controller   There are several CPU models:   Product order number (model) corresponding to processor name   PLC-5/10 1785-LT4   PLC-5/12 1785-LT3   PLC-5/15 1785-LT   PLC-5/25 1785-LT2       2. Enhanced PLC-5 controller   There are several CPU models:   1785-L11B、1785-L20B、1785-L30B、1785-L40B、1785-L60B、1785-L80B   DH+ or (and) remote input / output communication interface (Remote I/O) is generally provided.       3. Ethernet PLC-5 controller   There are several CPU models:   1785-L20E、1785-L40E、1785-L80E   For the above three CPUs, the Ethernet interface is a built-in standard configuration. DH+ or Remote I / O interface is also provided       4. Control network PLC-5 controller   There are several CPU models:   1785-L20C15、1785-L40C15、1785-L46C15、1785-L80C15。   The above four CPUs have built-in ControlNet network communication function, and also provide dh+ and remote input / output communication connection function.       5. Protective PLC-5 controller   There are several CPU models:   1785-L26B、1785-L46B、1785-L46C15、1785-L86B。 The safe controller allows the user to set access to "critical" or "private" program areas, protected memory areas, protected input and output, etc., and can also restrict the operation of the controller. Users can be classified and managed by programming software, so that they have different system permissions.       Except for the classic PLC-5 controller, the above five controllers are all equipped with 25 pin serial communication port.