Selection and design of various functional components of the control system:
1. The single-chip microcomputer used in this system is the 8031 model produced by Intel. This microcontroller serves as the core of the control system, handling signal processing through the parallel 8255 port. It receives signals for torque, valve opening, closing, and position, and provides the necessary control signals for the three-phase PWM wave generator. Additionally, it processes fault and alarm signals, interprets analog input signals such as current and voltage, and generates status signals for the actuator display. It also executes control commands from the system and sends feedback to ensure accurate operation.
2. For generating the three-phase PWM wave, the SA8282 chip from Mitel is employed. This dedicated integrated circuit offers a high-performance solution with an independent microprocessor interface. It contains waveform, frequency, and amplitude control information, making it ideal for precise and reliable control of the power module. Unlike traditional analog or digital methods, the SA8282 ensures better accuracy and system performance while allowing sufficient time for other critical functions like detection and protection.
3. The intelligent power module (IPM) used in this system is the PM50RSA120 from Japan. Designed for three-phase asynchronous motors under 5.5 kW, this IPM integrates the power switch, driver circuit, and braking function. It includes built-in protection features such as overcurrent, short-circuit, undervoltage, and overheating alarms, making it a robust and efficient power switching device suitable for high-reliability applications.
4. The position detection circuit plays a vital role in the actuator's operation by providing accurate position data. A pulse digital sensor is used instead of conventional potentiometers or differential transformers. This non-contact sensor offers high precision, stability, and no temperature limitations, ensuring long-term reliability and accurate positioning.
5. Voltage and current detection circuits are essential for monitoring motor torque, detecting short circuits, and performing phase failure protection. Hall-effect current transformers are used to quickly capture the three-phase current from the IPM output, while a voltage divider circuit measures the output voltage, ensuring real-time and accurate monitoring.
6. For communication purposes, the MAX232 chip is used as the serial interface between the microcontroller and external systems. It converts TTL levels to RS-232 standards, enabling seamless communication between the 8031 microcontroller and other devices, supporting remote control and network integration.
7. The clock circuit, based on the DS12887, provides accurate timing for sampling, control cycles, speed calculation, and calendar functions. It also includes 114 bytes of non-volatile RAM for storing long-term data, enhancing the system’s reliability and functionality.
8. A liquid crystal display (LCD) unit, specifically the MGLS12832 module, is used for human-machine interaction. It supports both text and graphical displays, allowing users to set and adjust parameters such as valve position, torque, and communication settings through an intuitive menu-based interface.
9. To ensure system stability in case of program interference, a self-recovery circuit using the MAX705 is implemented. This circuit monitors the microcontroller and triggers a reset if the program fails. After resetting, the system resumes normal operation, ensuring continuous and reliable performance even under adverse conditions.
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