Abstract
This paper introduces a method for troubleshooting and eliminating overflow alarm faults in fully automatic washing machines. It combines theoretical analysis with actual laboratory test results to confirm the fault causes through software and hardware analysis. Ultimately, it optimizes the control logic for overflow faults and the factory inspection methods for liquid level sensors.
Keywords：Washing machine, overflow, fault
Introduction
Currently, fully automatic washing machines have gradually become an indispensable household appliance in people’s daily lives. However, various faults may occur during the use of washing machines, affecting customer usage and experience, among which overflow faults are a common fault mode. The purpose of the overflow fault is to prevent users from experiencing water flowing out of the washing machine due to continuous water intake, which can damage other household items and lead to financial losses. Fully automatic washing machines generally use liquid level sensors to detect the amount of water intake. Liquid level sensors, also known as liquid level switches, play a crucial role in detecting the water intake and drainage of the washing machine, thereby controlling the washing machine’s water intake and drainage actions. If the liquid level sensor fails to detect accurately or malfunctions, it will lead to incorrect water intake, resulting in insufficient washing, water waste, and in severe cases, water overflowing from the washing machine drum, causing serious consequences.
1 Fault Case and Analysis
A prototype fully automatic pulsator washing machine occasionally triggered an overflow fault alarm during performance testing, but the actual water level did not reach the overflow level when the alarm was checked. The cause of the overflow fault was that the control system received a signal from the liquid level sensor indicating that the water level had reached the set alarm level. On-site verification showed that the actual water level was about 5 cm below the set overflow level. The maximum water intake was verified to be 60 L, while the actual flow meter detected an intake of 59.6 to 60 L, which did not meet the overflow condition. To clarify the cause of the fault, the software and hardware of the control system and the liquid level sensor were examined.
1.1 Hardware Inspection of the Main Control Board
To determine whether the main control board was causing the false alarm, a normally functioning main control board was replaced for verification, but the overflow fault still occurred. The only component affecting the input voltage to the liquid level sensor on the main control board was the voltage regulator. The output voltage of the voltage regulator ranged from 5.1 V to 5.5 V, and the measured output voltage during the fault was 5.35 V, indicating no issues with the voltage regulator. When simulating the upper and lower limits of the voltage regulator’s output, the frequency deviation detected by the liquid level sensor was only 20 Hz, while the allowable fluctuation range of the liquid level sensor was 0.4 kHz, so voltage fluctuations would not cause faults, thus ruling out component differences on the main board.
1.2 Software Program Inspection of the Main Control Board
Monitoring the operating data of the entire machine revealed that when the fault occurred, the frequency of the water level received by the main control board had exceeded the set overflow frequency value, and the program identified no anomalies. When the machine was running at t1, it detected a high water level, opened the drainage valve, and after detecting a normal water level, closed the drainage valve to continue operation. At t2, it again detected a high water level, triggering the overflow fault alarm, which was consistent with the logical settings. The above monitoring data indicated that the frequency value feedback from the liquid level sensor indeed output a signal exceeding the overflow protection set frequency, meeting the conditions for the controller to report an overflow protection fault.
1.3 Liquid Level Sensor Inspection
1.3.1 Working Principle of the Liquid Level Sensor
The liquid level sensor is installed at the top of the washing machine’s cabinet. It connects to the washing machine’s outer drum ventilation chamber through a tube, allowing it to monitor the air pressure inside the tube in real-time and convert that pressure signal into an electrical signal, which is then fed back to the control system to detect water level information. The liquid level sensors used in washing machines are generally mechanical and consist of components such as a housing, spring seat, magnetic core, pressure regulating spring, diaphragm, and pressure spring. The outer drum ventilation chamber of the fully automatic pulsator washing machine is connected to the liquid level sensor’s tube. When water is injected into the drum, the water level in the ventilation chamber gradually rises, and the pressure in the tube increases accordingly. The diaphragm inside the liquid level sensor deforms with the rising pressure, compressing the pressure spring to generate a pressure signal. The pressure signal corresponds to the water level signal, indicating when the pressure reaches a certain value that the water level has reached the set position, prompting the control system to stop water intake. When the water level decreases, the pressure in the liquid level sensor’s tube decreases, and the spring gradually resets. When it drops to the set water level, the control system receives the signal and can control the washing machine to perform the next action. If the liquid level sensor detects a deviation in the water level, such as when the control system receives a signal that the liquid level has reached the overflow level, the washing machine will exhibit an overflow fault.
1.3.2 Verification of Faulty Components of the Liquid Level Sensor
The liquid level sensor used in the machine exhibiting overflow faults was verified, and it was found that the frequency values at all levels met technical requirements, ruling out faults in the liquid level sensor itself.
1.4 Experimental Environment Inspection
Given that the parameters of the liquid level sensor in the faulty machine met the design specifications, the original factory inspection method had a large fluctuation range that could not detect faults. The factory inspection method was adjusted to use the entire machine with normal water intake and load to simulate actual usage conditions during inspection.
2 Analysis Summary
In conclusion, the occasional overflow fault that occurred during laboratory performance testing of the fully automatic pulsator washing machine was confirmed through analysis and experimental replication to be a false alarm caused by environmental vibrations affecting the liquid level sensor’s water level detection. This exposed the machine’s poor resistance to environmental disturbances, which needs optimization. Additionally, during the testing of new washing machines, various post-sale usage conditions should be simulated to introduce different environmental disturbances, allowing for early detection of potential fault types and subsequent rectification.
3 Prevention and Improvement
3.1 Logic Optimization
The overflow fault reporting logic of the entire machine was enhanced to include interference prevention criteria. The original detection scheme required that within time t, if the frequency exceeded the overflow frequency for 1 second, the machine would execute drainage actions until the normal water level was reached. If the frequency exceeded the overflow frequency again for another 1 second, it would report an overflow fault. The optimized approach requires that within time t, the frequency must exceed the overflow frequency continuously for 5 seconds, execute drainage operations until the normal water level is reached, and if the frequency exceeds the overflow frequency again for another 5 seconds, it will report an overflow fault. If the exceedances are not continuous, the detection will reset for the next check.
3.2 Optimization of the Liquid Level Sensor Inspection Method
The original factory inspection method for the liquid level sensor involved using a pressure pump to maintain a constant pressure for testing. However, during actual usage, the washing process involves shaking, which causes fluctuations in the water surface and pressure. The original factory inspection method had a large fluctuation range that could not detect faults. The inspection method was adjusted to use the entire machine with normal water intake and load to simulate actual usage conditions for inspection.
To enhance the interference resistance of fully automatic washing machines and prevent user inconvenience caused by false faults, thereby improving user satisfaction and market competitiveness, the following measures can be taken during product development and production:
Conduct a comprehensive analysis of various fault codes during the development phase to confirm alarm thresholds, as well as the inherent fluctuation factors and environmental disturbance factors during use, and develop anti-interference measures.
Combine the inspection of components with actual usage environments to establish reliable inspection methods, preventing component fluctuations from causing overall machine faults.
Improve testing methods based on product characteristics and usage conditions, introducing environmental disturbance factors to conduct adverse condition testing on the entire machine to identify issues early and optimize solutions.