Abstract : This paper introduces a ventilation fan speed control monitoring system using an Omron PLC as the master station and serial communication with 14 Omron 3G3MZ series frequency converters via RS-485 bus. The driving mechanism of the fan's frequency conversion speed control, the system's hardware configuration, and the communication implementation method between the PLC and the frequency converters are described in detail. The advantages of this network control speed control system compared to general analog control speed control systems are explained. A system block diagram and the software implementation method of the PLC system are provided. Practical application demonstrates its good anti-interference performance, high reliability, and practicality. Keywords : PLC; RS-485; frequency conversion speed regulation; analog quantity CLC classification number: TP273 Document identification code: A Abstract : Recommend regarding Omron PLC as the main website, pass RS-485 bus and 14 3G3MZ series serial news reports of frequency converter of Taiwan Omron, and realize the frequency converter of the ventilator adjusts the monitoring system of the speed. Describe the frequency conversion of the air blower adjusts the drive mechanism of the speed, the systematic hardware forms in detail, PLC and communication implementation method of frequency converter, expound network this control, transfer speed to be systematic to control, transfer superiority that speed compares systematically with general analog quantity. Provide the systematic block diagram and PLC system software implementation method. It proves its anti-interference is good, dependability is high, practicability is good that practical. Key words: PLC, RS-485, Variable Voltage Variable Frequency, Analog 0 Introduction Fan equipment is widely used in industrial control. Traditional fan control is full speed operation, that is, regardless of the size of the production process, the fan provides a fixed amount of air volume, while the production process often requires control and adjustment of wind speed and air volume. The most common method is to adjust the controlled object by adjusting the size of the damper or baffle opening. In this way, a lot of energy is consumed by the interception loss of the damper and baffle. With the continuous improvement of AC speed regulation technology and the continuous development of frequency conversion technology, the use of frequency converters for speed regulation is becoming more and more widespread. After the ordinary motor adopts frequency conversion speed regulation, the speed output can be adjusted according to the production process requirements without any modification to the load it drives. Therefore, the fan equipment can completely replace the damper and baffle control scheme with the frequency converter drive scheme, thereby reducing the power consumption of the motor and achieving the purpose of efficient system operation. 1 Fan frequency conversion speed regulation drive mechanism [1] As we all know, using the AC voltage with adjustable frequency output of the frequency converter as the power supply voltage of the fan can easily change the speed of the fan. From the load characteristics of the fan, it can be seen that the mechanical characteristics of the fan have a quadratic law characteristic, that is, the torque changes proportionally to the square of the speed. At low speed, the fluid velocity is low, so the load torque is very small. As the motor speed increases, the velocity increases, and the load torque and power are the torque constant and power constant of the quadratic law load, respectively. Therefore, when the required air volume of the controlled object decreases, the frequency converter is used to reduce the speed of the fan, which will greatly reduce the power consumption of the motor. 2 Hardware Design (1) PLC Selection and I/O Address Allocation In order to meet the reliability and good control accuracy and stability of the fan control system, we selected the Omron CP1H series 40-point transistor output PLC and externally expanded a 40-point relay output CPM1A-40EDR module as the basic unit. The system controls each frequency converter according to the status of the decontamination cabinets on each floor. There are 37 decontamination cabinets and one manual/automatic switch with a total of 38 input points. The output controls the status display, alarm signal (transistor output) and start/stop of the frequency converters (relay output) of 14 frequency converters. (2) Frequency converter selection: Omron 3G3MZ series frequency converter is selected. The SYSDRIVE 3G3MZ series is a high-performance frequency converter equipped with vector control. Due to the automatic adjustment function of the motor, it can achieve powerful control more easily with vector control than V/f control. It is equipped with RS485 as standard. In addition, by adding options, it can be compatible with various networks and can also provide the further control required for the system construction connected to PLC. The single-phase 200VAC type and the three-phase 400VAC type of the frequency converter have built-in noise filters corresponding to CE specifications. The existing models are equipped with detachable operators, PID control, energy-saving control and other rich functions. (3) Touch screen selection: Omron NT5Z series touch screen is the operation setting display unit of the whole system. On the touch screen, the PLC internal data, input and output status, various parameters and status of the frequency converter, alarm information, etc. can be displayed through different screens, and the working status of the whole machine can be monitored in real time. In addition to the display function, some parameters that need to be set by the user can be set and modified in the PLC through the touch screen according to the on-site situation. The working status of the frequency converter can be directly observed through the human-machine interface, and the frequency converter control system can be monitored in real time. The system structure diagram is shown in Figure 1. [align=center] Figure 1 Systematic structure chart[/align] 3 Software Design 3.1 Manual and Automatic Operation Modes (1) Manual Operation When the system is powered on, the two-way switch on the control panel is switched to manual mode, and the system is in manual operation mode. The manual operation screen is shown in Figure 2. When the system is in manual operation, regardless of whether the frequency converter is running, the frequency value of the frequency converter is entered through the frequency input box, and the frequency value is written to the frequency converter. The write range is 0～50HZ. Press the start/stop button to control the start and stop of the frequency converter. Note: When the system is in automatic operation, the "start/stop" and frequency input on the manual screen are invalid. The manual operation mode is mainly used for maintenance and frequency converter failure. Under normal circumstances, the system works in automatic mode. [align=center] Fig.2 Automatic operation picture[/align] (2) Automatic operation When the system is powered on, the two-way switch on the control panel is switched to manual mode, and the system is in automatic operation mode. The system automatically calculates the Hertz number of the frequency converter according to the number of decontamination cabinets opened by the user. During the actual operation of the system, the user can adjust the operating frequency of the frequency converter by setting the starting frequency according to the actual situation. Setting the starting frequency does not affect the normal operation of automatic operation. The automatic operation screen is shown in Fig.3. [align=center] Fig.3 Automatic operation picture[/align] When the system is in automatic operation mode, the frequency of each frequency converter is automatically calculated by the system. Note: ① The frequencies of 7P1, 7P2, 7P3, 6P1, 6P2, 5P1, 5P2, 5P3, and 5P4 are automatically calculated from the input decontamination cabinet status. ② The frequency of 9P1 is calculated from the input decontamination cabinet status of 5P2, 5P3, 6P1, 7P1, and 7P2. ③ The frequency of 9P2 is calculated from the status of the exhaust cabinets input to 5P1, 5P4, 6P2, and 7P3. ④ The frequency of 7X1 is calculated from the status of the exhaust cabinets input to 7P1, 7P2, and 7P3. ⑤ The frequency of 6X1 is calculated from the status of the exhaust cabinets input to 6P1 and 6P2. ⑥ The frequency of 5X1 is calculated from the status of the exhaust cabinets input to 5P1, 5P2, 5P3, and 5P4. 3.2 Communication between PLC and frequency converter [7] (1) Communication connection: CP1W-CIF11 is used on the CP1H side. The CP1W-CIF11 switch settings are: ① 1=ON (terminal resistor); ② 2,3=ON (RS485 mode); ③ 5=ON (do not echo back data); ④ 6=ON (RS485 mode). (2) Inverter basic parameter settings [6]: ① "n0.02" Disable parameter selection: Set to "9", initialization at the highest frequency of 50HZ. ② "n2.00" Frequency command selection: Set to "4", frequency commands sent by RS485 communication are valid. ③ "n2.01" Operation command selection: Set to "1", the STOP key of the control circuit terminal operation is also valid. ④ "n2.05" Operation selection after power-on/operation switching command: Set to "2", valid after power-on/operation switching command. ⑤ "n9.00" RS485 communication slave address: Set slave address. ⑥ "n9.02" Action when RS485 communication error is detected: Set to "0", display warning and continue operation. (3) CP1H Program Settings [7] For ease of use, Omron has introduced a function block that supports communication with the 3G3MZ, 3G3RV and 3G3MZ inverters. It is applicable to Omron's CS1/CJ1 (CPU V3.0 and above) series communication boards and communication units (versions that support serial port gateway function) and the built-in communication port of CP1H. The port protocol is selected as Serial-Gateway. The function block usage is shown in Table 1 below. [align=center]Table 1 Function block usage table Tab.1 Function block the use of table[/align] The Refresh function block must be used. All other function blocks are based on this function block for communication. The specific parameter settings are as follows. CP1H sets the Uint selection to #CCCC, SCB to #BBBB, and SCU to &0-&15. The Scan list No settings are as follows: Bit0 corresponds to broadcast, Bit1 to station 01, and Bit2 to station 02. If both stations 01 and 02 are connected simultaneously, set it to 00000006. This parameter cannot be modified during communication, otherwise unpredictable results will occur. The I/F Area ID is the two-word parameter for reading/writing the inverter, and the Message Area ID is the command response status. However, when calling other function blocks, the same area and address need to be set. The Refresh function block is shown in Figure 4. [align=center] Figure 4 Refresh Function Block Fig.4 Refresh Automatic operation picture [/align] 4 Conclusion In this solution, multiple inverters are controlled entirely through the PLC's 485 bus. The operating speed of each motor can be monitored and set online. Furthermore, since the inverters and PLC are installed at a considerable distance, interference from the inverters to the PLC is reduced. The system has the advantages of simple hardware, high reliability, strong anti-interference ability, and good practicality. References [1] Shi Zengfang, Jiang Yanlei, Huang Zongjian. Fan speed control system based on frequency conversion technology [J]. Industrial and Mining Automation, 2007.1: 97-99 [2] Li Bin, Fu Yongyi. Bus control of multiple frequency converters [J]. Microcomputer Information, 2006.8: 18-20 [3] Zhong Zhaoxin. Programmable control: its principles and applications [M]. South China University of Technology Press, 2004 [4] Liu Zhen. Application of PLC in frequency conversion operation of three-phase AC step motor [J]. Industrial and Mining Automation, 2005.10(5): 69-70 [5] Wu Wei, Wu Guanhua, Yu Jinke. Implementation and application of PLC and multiple frequency converters based on RS-485 communication. Automation Instrumentation, 2005, 26(9): 55-57 [6] Omron 3G3MZ Operation Manual [7] OMRON CP1H Programming Manual First Author Zhou Hongli, female, born in 1982, is currently a master's student in the School of Computer Engineering at Qingdao University of Technology. Her main research direction is the design of computer control and detection systems. Contact information: P.O. Box 284, Qingdao University of Technology, No. 11 Fushun Road, Sifang District, Qingdao, Shandong, 266033, China. E-mail: [email protected] Tel: 0532-85071298