The hottest liquid level control design of frequen

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PLC based inverter liquid level control design

Abstract: in this system, For reality "This high-speed injection molding machine can produce 100 fast-food box covers in one minute. In order to make full use of the existing energy and meet the needs of production, it is necessary to adjust the speed of the motor. Considering the characteristics of motor startup, operation, speed regulation and braking, ABB frequency converter is used. In the system, PLC completes the data collection and control tasks of frequency converter, motor and other equipment. Based on S7 200 PLC programming software, modular programming method is adopted, and a large number of Use code reuse to reduce software development and maintenance. Using the design of PLC software, the parameter setting, fault diagnosis of frequency converter and the start and stop of motor are realized

key words: PLC inverter variable frequency speed regulation with the development of power electronics technology and industrial automatic control technology, AC variable frequency speed regulation system has been widely used in the field of industrial motor drive. In addition, because of its powerful function, easy to use and high reliability, PLC is often used as a field data acquisition and equipment control. This design is to use frequency converter and PLC to control the water level of the pool. Inverter technology is a comprehensive technology, which is based on control technology, electronic power technology, microelectronics technology and computer technology. Compared with the traditional AC drive system, it has many advantages, such as power saving, easy to realize the speed control of the existing motor, high-efficiency continuous speed control in a large range, and accurate speed control. It is easy to realize the forward and reverse switching of the motor, and it can carry out a high amount of start and stop rotation, electrical braking, and high-speed drive of the motor. Perfect protection function: the frequency converter has a strong protection function, which can detect various faults at any time during operation, display the fault category (such as instantaneous voltage reduction, phase loss, DC overvoltage, overheating of power module, motor short circuit, etc.), and immediately block the output voltage. This "Self-protection" function not only protects the frequency converter, but also protects the motor from damage. PLC features: first, high reliability, strong anti-interference ability, and the average failure time is hundreds of thousands of hours. Moreover, PLC adopts many hardware and software anti-interference measures. Second, the programming is simple and easy to use. At present, most PLC adopts the ladder diagram programming method in the form of relay control, which is easy to be accepted by operators. Some PLCs also design step ladder instructions according to specific problems, which further simplifies the programming. Third, the design and installation is easy and the maintenance workload is less. Fourth, it is suitable for harsh industrial environment. It is packaged and suitable for various applications such as vibration, corrosion, toxic gases, etc. Fifth, it is convenient to connect with external equipment. The removable movable terminal strip with unified wiring mode provides different terminal functions, which is suitable for a variety of electrical specifications. Sixth, it has perfect functions, strong versatility, small size, low energy consumption and high performance price ratio. In the application of PLC system design, the following basic principles should be followed to ensure the stability of the system. (1) Meet the control requirements of the controlled object to the greatest extent; (2) The system structure should be simple; (3) The system should work stably and reliably; (4) The control system can be easily extended and upgraded; (5) Friendly man-machine interface. In this system, in order to realize the full utilization of energy and the needs of production, it is necessary to adjust the speed of the motor. Considering the characteristics of motor startup, operation, speed regulation and braking, abb ACS800 frequency converter of ABB company is used. In the system, S-Series PLC completes the data collection and control tasks of frequency converter, motor and other equipment. The programming software based on s PLC adopts modular programming method and a large number of code reuse to reduce software development and maintenance. The system uses the design of PLC software to realize the parameter setting of frequency converter, fault diagnosis and the start and stop of motor. 1. Control requirements of this design: 1) the system requires users to intuitively understand the working state of field equipment and the change of water level; 2) The user is required to be able to remotely control the start and stop of the frequency converter; 3) Users can set the water level by themselves to control the start and stop of the frequency converter; 4) The fault information of frequency converter and other equipment can be timely reflected on the remote PLC with the continuous improvement of innovation ability in technology, research and development and product processing; 5) It has the functions of alarming and prompting users when the water level is too high or too low; 2. Control structure of this design: since there is a motor as the controlled object on site, a single PLC can be used to control a single object. As long as a high-performance PLC is properly selected, it can completely surpass the thin metal sheet and metal frame in the exhibition cabinet. The system control structure is shown in Figure 1. PLC collects the information of various objects related to sensors, monitoring motors and frequency converters. In this system, a frequency converter is used to regulate and control the frequency of the motor. The analog signal output by PLC is used as the input signal of the control end of the frequency converter, so as to control the speed of the motor, and feed back its own working state signal to PLC. When a fault occurs, it can send an alarm signal to PLC. Since the variable frequency speed regulation is realized by changing the power supply frequency of the motor stator to change the synchronous speed, the limited slip power can be maintained from high speed to low speed in the speed regulation process, so it has the speed regulation performance of high efficiency, wide range and high precision. 3. Equipment selection (1) selection of PLC and its expansion module: at present, we strengthen the research and development of key core technologies of new materials. There are a wide variety of large, medium and small PLC, ranging from being a substitute for a small number of relay devices to being a host computer in a distributed system, which can almost meet the needs of various industrial controls. In addition, new PLC products are still emerging, so how to choose a suitable PLC? The system has a motor, a liquid level sensor, a frequency converter, five relays, a total of eighteen i/o points, which constitute the controlled object. Comprehensively analyze the characteristics of all kinds of PLC, and finally choose Siemens S7 Series PLC. Since cpu226 integrates 40 digital i/o points with 24 inputs/16 outputs, it can fully meet the control requirements. This PLC can be connected with 7 expansion modules, and the maximum expansion is 248 digital i/o points or 35 analog i/o points. 26k bytes

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