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Design scheme of electric kettle temperature control switch life tester

The electric kettle is damaged or does not work properly, most of which is caused by damage to the temperature control components. Therefore, this paper proposes a design scheme for a life tester for temperature-controlled switches. The solution can estimate the life of the temperature control component, and thus can achieve the purpose of prolonging the life of the electric kettle by improving the temperature control switch.

The test instrument designed by this scheme is mainly used for the life test of the kettle temperature control switch. The test sample is installed and the tester can automatically complete the life test of the temperature control switch. No manual intervention is required during the test phase, and sound and light indications can be made at the end of the test or on the way to a fault. It has been verified that the instrument can achieve automated work, greatly reducing the workload of testers and improving test efficiency.

In recent years, exquisite, practical, convenient and fast electric kettles have begun to enter thousands of households. After more than ten years of development, the electric kettle industry has a domestic tens of millions of units. China has become the world's largest electric kettle market with broad development prospects. It is estimated that it is only in Guangdong, and the annual output of electric kettles exceeds 30 million units. However, the latest spot check shows that about 30% of the electric kettles on the market are unqualified, making it difficult to protect the consumer rights of the kettle. The industry has low barriers to entry, small scale enterprises, and poor quality awareness of workshop-style enterprises are the most direct causes of poor quality of electric kettles. In order to regulate the electric kettle market and protect the rights and interests of consumers, the safety standard of China's "Electric Kettle Performance Requirements and Test Methods" was implemented in May 2009.

The quality of the electric kettle products is unqualified, and more than 90% of them are caused by the failure of the electric kettle. The electric kettle switch has a short life span and is prone to failure. It cannot be boiled after a period of use. The purpose of this paper is to develop and design an electric kettle tester for testing the life of the electric kettle switch, that is, the number of times the electric kettle switch is turned on. The tester does not need to participate in the art, as long as the switch is installed the test sample. When the test is completed or the fault occurs, the sound and light indication can be given, and the fully automated work can greatly reduce the workload of the tester and improve the efficiency. The tester studied in this paper has certain innovation, practicability and engineering, and it has been put into use in Lianjiang Di Aisi Electric Appliance Factory with good effect and certain economic and practical significance.

Temperature control switch structure and easy problem parts
The structure of the temperature control switch is shown in Figure 1. The main purpose is to use a dish-shaped bimetal as a temperature sensing component. As shown in Figure 2, the working principle of the temperature control switch is:
When the temperature rises, the disc will deform accordingly. When the temperature reaches a value at which the disk is deformed, the jump of the disk depends on the mechanical transmission of the other device, causing the contact to act quickly to turn the current on or off. Operating temperature range: 30 ° C -300 ° C.
Bimetal structure of temperature control switch

The temperature control switch is prone to three problems:
First of all, when the temperature of the bimetal disc of the temperature control switch itself is too high, the steam of the electric kettle cannot make the bimetal disc reach the jumping temperature, so that the temperature control switch cannot cut off the current. The water in the electric kettle has been boiling and cannot be stopped to cause danger; Secondly, the bimetal is a mechanically processed part, and the jump and reset have a mechanical life. Material problems or processing problems have a direct impact on the life of the bimetal. Assume that a kettle is used 5 times a day for 1 day. It is close to 2,000 times a year. To ensure that the kettle is used for more than 5 years, it is necessary to ensure that the temperature control switch or bimetal has a life of more than 10,000 times; The small spring of the last temperature-controlled switch, like the bimetal, is also a mechanically machined accessory. Its life also directly affects the life of the temperature control switch and even the electric kettle. Therefore, research and design of the temperature control switch life tester is essentially a life tester for testing bimetal and jump small springs. In the actual production test, the test is selected by sampling.

Technical solution of temperature control switch tester
The overall system diagram of the test instrument is shown in Figure 3 and can be divided into three parts:
Circuit part, mechanical part and mounting base part.
Temperature control switch tester design

First, the board part:
This part takes the microcontroller (MCU) as the core of intelligent control. The water temperature of the test kettle is collected by the DS18B20 temperature sensor and sent to the MCU for processing and displayed in an LED or digital tube. When the test encounters a fault or the test is completed, an appropriate sound and light indication is issued. The circuit schematic is shown in Figure 4.
Temperature control switch tester circuit schematic

second, Mechanical part: The electromagnet opens and closes to control the switch to open and close. Test the kettle to provide true AC220V voltage and 1500W power loaded on the contacts of the switch. The mechanical structure is shown in Figure 5.

Thermo-controlled switch tester electromagnetic mechanical structure diagram

Third, the base part: Fix the tester's circuit board, electromagnet, temperature control switch and switching power supply.
Fourth, the software part: Program development is performed on the underlying MCU using C-voice. The program flow chart is shown in Figure 6.
Temperature control switch tester program flow
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