A design scheme of temperature control switch life tester

Abstract: In recent years, exquisite, practical, convenient and fast electric kettles have begun to enter thousands of households, and China has become the world's electric kettle market. But according to the data:

Most of the damage or failure of the electric kettle is caused by the damage of the temperature control components. Therefore, this paper proposes a design plan for the life tester of the temperature control switch, which can estimate the life of the temperature control components, and then The purpose of extending the life of the electric kettle can be achieved by improving the temperature control switch.

The test instrument designed in this program is mainly used for the life test of the kettle temperature control switch. After the test sample is installed, the tester can automatically complete the life test of the temperature control switch. The test phase does not require manual participation, and the test can be issued after the end of the test or a fault occurs on the way. Sound and light instructions. It has been verified that the instrument can realize automated work, greatly reducing the workload of testers and improving test efficiency.

  0 Preface

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 currently owns tens of millions of electric kettles in China. China has become the world's electric kettle market with broad prospects for development. It is estimated that the annual output of electric kettles in Guangdong alone exceeds 30 million. However, spot checks show that about 30% of electric kettles on the market are substandard, making it difficult to protect the rights and interests of consumers who purchase kettles. Low barriers to entry in the industry, few large-scale enterprises, and poor quality awareness of workshop-type enterprises are the direct reasons for the poor quality of electric kettles. In order to regulate the electric kettle market and protect the rights and interests of consumers, my country's "Electric Kettle Performance Requirements and Test Methods" safety standard has been implemented in May 2009.

The quality of the electric kettle is unqualified. More than 90% of it is caused by the failure of the switch of the electric kettle. The switch of the electric kettle has a short life and is prone to failure. The phenomenon that the water cannot be boiled after a period of use. The purpose of this paper is to develop and design an electric kettle tester, which is used to test the life of the electric kettle switch, that is, the number of times the electric kettle switch is turned on. The tester does not require personnel to participate, as long as the test sample switch is installed, the test is completed or malfunctions can emit sound and light instructions, fully automated work, greatly reducing the workload of testers and improving efficiency. The tester studied in this paper has a certain degree of innovation, practicability and engineering, and it has been put into use in Lianjiang Diaisi Electrical Appliance Factory. The effect is good, and it has a certain economic effect and practical significance.

1 Temperature control switch structure and problem-prone parts

The structure diagram of the temperature control switch is shown in Figure 1, which mainly uses a disc-shaped bimetal as the temperature sensing component. As shown in Figure 2, the working principle of the temperature control switch is: when the temperature rises, the disc Corresponding deformation will occur, and when the temperature reaches the value of the disc deformation, the sudden jump of the disc depends on the mechanical transmission of other devices to make the contacts move quickly to switch on or cut off the current. Operating temperature range: 30℃ -300℃.



The temperature control switch is prone to three problems: First, when the temperature of the bimetal disc of the temperature control switch jumps too high, the steam of the electric kettle cannot make the bimetal disc reach the jump temperature, causing the temperature control switch Unable to cut off the current, the water in the electric kettle is always boiling and cannot stop causing danger; secondly, the bimetal is a mechanically processed accessory, and the jump and reset have mechanical life. Material problems or processing problems have a direct impact on the life of the bimetal. Assuming that a kettle is normally used 5 times a day as an example, it is close to 2000 times a year. To ensure that the kettle is normally used for more than 5 years, the temperature control switch or the bimetal must be guaranteed to have a life of more than 10000 times; temperature control switch Like the bimetal, the small spring is also a mechanically processed accessory, and its life span also directly affects the life of the temperature control switch and even the electric kettle. Therefore, the research and design of the temperature control switch life tester is essentially a life tester for testing bimetallic strips and small jump springs. In the actual production test, the sampling method is selected for testing.

2 Technical scheme of temperature control switch tester

The overall system diagram of the test instrument is shown in Figure 3 and can be divided into 3 parts:

The circuit part, the mechanical part and the installation base part.



, Circuit board part: This part is intelligently controlled by a single-chip microcomputer (MCU). It collects the water temperature of the test kettle through the DS18B20 temperature sensor, transmits it to the MCU for processing, and displays it in the LED or digital tube. If the test encounters a failure or the test is completed, it will Give out corresponding sound and light instructions. The circuit schematic diagram is shown as in Fig. 4.



Second, mechanical part: the opening and closing part of the electromagnet, to control the switch on and off, test the kettle, and provide real AC220V voltage and 1500W power to be loaded on the contacts of the switch. The mechanical structure diagram is shown in Figure 5.



Third, the base part: fixed circuit board, electromagnet, temperature control switch and switching power supply of the tester.

Fourth, the software part uses C voice to develop programs for the bottom-level MCU. The program flow chart is shown in Figure 6.



3 Working test process

The temperature control component tester of the electric kettle can simulate the working conditions of the electric kettle switch. It can be connected to the AC220V voltage and connected to a 1500w electric heating wire for testing. It can not only automatically count and accumulate the number of switch ons, but also control the electric kettle to cook. The temperature of the water keeps it constant within a temperature range without boiling the water and evaporating it.

The tester is intelligently controlled by STC12C5a60s2 (MCU). It collects the water temperature of the test kettle through the DS18B20 temperature sensor, transmits it to the MCU for processing, and displays it in the LED or digital tube. The MCU obtains the water temperature data from the electric kettle as the basis for control judgment, and controls the opening and closing of the electromagnet to control the on and off of the temperature control switch. The tested kettle provides real AC220V voltage and 1500W power, which is loaded on the switch contacts At the same time, the AC220V is converted into an AC9V signal through a transformer, after rectification and filtering, it becomes a PWM mode DC11V control signal, which controls the opening and closing of the transistor circuit, and sends the opening and closing data of the temperature control switch to the MCU control chip, and the MCU according to the switch connection data The number of times the switch is turned on is accumulated and displayed in the LED or digital tube. When a failure occurs or after 10,000 tests are completed, the MCU can control the temperature control switch to be in an off state to prevent the kettle from heating all the time, boil the water dry, and give out corresponding sound and light instructions.

4 Summary

The temperature control switch detection has always plagued the development of the temperature control industry. The detection by humans is not only inefficient, but also due to human factors, errors may occur during work, which will affect the quality of the entire product. Therefore, this paper proposes a design plan for the life tester of temperature-controlled switches, research and development of semi-automatic and fully-automatic temperature-controlled switch testing equipment. The version of the temperature control tester designed in this program has a simple structure, low price, and stable performance. It has been put into trial use in Lianjiang Diaisi Electrical Appliance Factory, which has a good effect, and has a certain economic effect and practical significance. (Author: Gan Yanfen, Zhang Xinqiang, Deng Jinghui)