Preface: Many control systems are composed of microcontrollers, etc. The normal operation of a microcomputer control system depends on many factors, including various external interferences and the inherent quality of the system itself. External interferences can generally be overcome by adopting appropriate anti-interference measures. However, errors in various chips, electronic components, circuit boards, etc., can affect the overall system quality. Therefore, to improve hardware reliability, it is essential to take hardware fault diagnosis measures to promptly diagnose hardware fault types and ensure timely system operation. 1. System Hardware Composition The core of this system is an 8098 microcontroller, mainly responsible for electro-hydraulic position servo control. The system block diagram is shown in Figure 1. [IMG=System Block Diagram]/uploadpic/THESIS/2007/12/2007121509471622682H.jpg[/IMG] To meet the requirements of control performance and reliability, and to improve the system's anti-interference capability, strict isolation measures are adopted between the microcontroller and the input/output channels. The input channel employs dual-line sampling, differential input of an instrumentation amplifier (AD624), isolation amplification of a linear isolation amplifier (AD202), and four active filters to effectively suppress external interference. The controller's control output uses a high-precision, high-speed output HSO.0 to obtain PWM output, which is then optocoupled and filtered by an active filter to obtain DC control voltage, which is sent to the servo amplifier to ultimately control the controlled object. 2. Implementation of Fault Diagnosis Process The system is equipped with fault diagnosis functions for the CPU, program execution, RAM, EPROM, input/output channels, and servo amplifier. The system fault test block diagram under the premise that the CPU is fault-free is shown in Figure 2. [IMG=System Fault Test Block Diagram]/uploadpic/THESIS/2007/12/2007121509475146841J.jpg[/IMG] 2.1 CPU Fault Diagnosis CPU program execution fault diagnosis utilizes the signals and functions provided by the microcontroller itself, combined with simple circuits to form a fault diagnosis system for detection. Whether the CPU is working properly or not is directly monitored by the hardware fault diagnosis module through the chip's signal. When the CPU is working properly, it continuously performs read and write operations, and the signal shows alternating high and low levels. If there is no level change, the CPU is working abnormally, and the diagnosis module outputs a fault signal. Program execution faults are detected by the software fault diagnosis module by detecting changes in the CPU chip's RESET signal. During normal operation, the signal is at a high level, and it is only clamped to a low level in the case of power-on reset, overflow, or instruction RST reset. A feature flag is set in the system to distinguish between normal reset and fault reset. The method is as follows: if a normal reset is found through the feature flag, the recorded data is cleared; if a fault reset is found, the recorded data is retained. After the data reaches N times, the software fault diagnosis module outputs a fault signal. 2.2 Input Channel Fault Diagnosis The A/D channel of the analog input signal is a time-division multiplexer, and a multiplexer (4052) is used to select the analog input signal. All analog input signals share the A/D converter in the 8098 microcontroller [1]. Analog input channel faults include A/D converter faults, isolation amplifier faults, differential amplifier faults, and multiplexer faults. Testing each of these faults individually would significantly increase hardware requirements and make the system extremely complex. To avoid excessive system complexity, a unified test is performed on the entire input channel. The test method involves applying two special signals (5V and 0V) to the input terminal of the multiplexer at the very beginning of the input channel. By testing the conversion results of these two special cases, the normality of the analog input channel is determined. The test block diagram is shown in Figure 3. RAM and EPROM fault diagnosis is performed using software [2]. [IMG=Test Block Diagram]/uploadpic/THESIS/2007/12/2007121509480631647G.jpg[/IMG] 2.3 Position Sensor Fault Detection If a potentiometer experiences a short circuit or open circuit, or if the connecting wires connected to it experience a short circuit or open circuit, the system will not function properly. Therefore, real-time fault diagnosis is essential. According to the specific installation process of the potentiometer, when the circuit and potentiometer are normal, the output voltage of the potentiometer cannot have two voltage levels: 0V and 5V. Only when there is a fault in the potentiometer and its wiring will these two voltage levels occur. If, during operation, the input voltage is measured to be 0V or 5V when the input channel is fault-free, it indicates a sensor fault. When a fault is detected, necessary measures can be taken for timely repair. The test block diagram is shown in Figure 4. [IMG=Sensor Fault Detection Diagram]/uploadpic/THESIS/2007/12/2007121509481424841F.jpg[/IMG] 2.4 Output Channel and Servo Amplifier Fault Diagnosis Faults in the output channel and servo amplifier will lead to damage to the proportional valve; therefore, a fault diagnosis circuit for the output channel and servo amplifier must be designed. The specific design scheme is as follows: The analog output signal is output from the high-speed output (HSO.0) terminal of the 8098. After the electrical parameters of the output channel and servo amplifier are adjusted, each output value of HSO.0 corresponds to a basically fixed load current. When HSO.0 outputs with a certain duty cycle, the load current is detected by the measurement channel to see if it is within the corresponding range. If it is not within the range, it indicates that there is a fault in the analog output channel or servo amplifier. The test block diagram is shown in Figure 5. [IMG=Output Channel and Servo Amplifier Fault Diagnosis]/uploadpic/THESIS/2007/12/20071215094822933743.jpg[/IMG] The diagnostic system designed in this paper was used in the hardware fault diagnosis system of the electro-hydraulic position servo control system of electric arc furnace steelmaking in 1996. It has a certain degree of accuracy and reliability and has promotion value. References: 1. Li Zheying, Xiao Haiqiao, Yu Wenlong. Principles and Applications of Microcontrollers. Beijing: Tsinghua University Press, 1995, pp. 75-76. 2. Zhou Hangci. Microcontroller Application Programming. Beijing: Beijing University of Aeronautics and Astronautics Press, 1992, pp. 56-60.