Detailed description of home appliance thermostat life test device
KSD301 thermostats are widely used in a variety of home appliances, such as refrigerators, water dispensers, water heaters, coffee makers, induction cookers, microwave ovens, rice cookers, etc. The quality of the appliance thermostat directly affects the safety, performance and life of the whole machine, and is a key thermal protection component. Among the many technical indicators of thermostats, life is one of the most important technical indicators for measuring thermostat products. The appliance standard stipulates that the life of the thermostat is at least 10,000. Some home appliances, such as thermostats that control motor-compressors in refrigerator products, require some thermostats in liquid-filled radiators to have a life expectancy of at least 100,000. The standard for household thermostats GB14536.10-2008/IEC60730-2-9:2004 has detailed requirements for the life test of the thermostat.
At present, there are many manufacturers of temperature controller life test devices on the market, each with its advantages and disadvantages, and the main disadvantages are the rocker arm structure. During the test, the installation of the thermostat deviates from the actual situation, the thermal inertia of the heating body is greatly affected, and the life of the thermostat is greatly affected, resulting in inaccurate test results; The adjustable range of the thermostat is small and can not meet the standard requirements; The life test device is complicated to maintain and always replace the heating body; The test device has a narrow application surface; The equipment is complicated to operate and expensive. Based on years of experience in thermostat testing, the author designed a simple test device. The equipment has been put into use, and the actual use proves that the device has strong versatility, close to the actual working condition, the test result is accurate, and the cost is low.
2, home appliance thermostat standard requirements
2.1 Electrical conditions of the test
Each circuit of the appliance thermostat shall be tested according to the rated load of the manufacturer as the basic technical parameters.
2.1.1 Over-voltage test of fast automatic action
A 1.15 times rated voltage and an electrical load at this voltage are used.
2.1.2 Test of fast automatic action
The rated voltage and the electrical load at this voltage are used.
2.2 Thermal conditions of the test
When the thermostat is installed in accordance with the manufacturer's instructions, accessible parts should be exposed to normal room temperature.
2.3 Mechanical conditions of the test
2.3.1 During the slow test, the test equipment shall drive the starting element reliably, with no significant hysteresis between the equipment and the starting element.
2.3.2 During the rapid test, the test equipment shall ensure that the test allows the starting element to operate freely so as not to interfere with the normal operation of the mechanism.
3, home appliance thermostat test device introduction
3.1 Equipment parameters
Test voltage: 0-300VAC adjustable; electrical load: 1 ~ 24A adjustable;
Test frequency setting range: 1000-99999; heating temperature adjustment range: room temperature to 500 ° C; cooling air pressure: 0 ~ 1 MPa;
Station: 3; self-contained resistance load table, and external load table; preset test times, cycles;
It has the function of automatic detection and failure of test sample failure; and shows the number of tests.
3.2 Equipment principle
The device is mainly composed of four parts:
The temperature rising portion, the air flow cooling portion, the load portion, and the detection control display circuit are as shown in FIG.
Figure 1 Equipment composition
3.3 Home appliance thermostat function flow
Taking a normally open thermostat as an example, a temperature-sensitive sensitive portion is mounted on the surface of the heating block. Adjust the electrical load required by the sample, and set parameters such as heating block temperature, fault alarm time, and number of life. Adjust the cooling gas pressure to keep the working frequency consistent with the technical requirements, start the test, and the test flow is shown in Figure 2.
3.4 Main structure of home appliance thermostat equipment
The method of heating and cooling is the most important part of the thermostat life test device.
The heating of the device is realized by means of a copper block and an electric heating tube, and the electric heating tube is placed inside the copper block, and the heating is controlled by a PID method. After the heating tube is energized, the copper block is heated, and the temperature at which the thermocouple is collected on the surface of the copper block to collect the copper block in real time is compared with the preset temperature. As shown in Figure 3.
This kind of heating method has good thermal conductivity of copper, and the temperature field uniformity of the surface is good, so that the heating temperature can be precisely adjusted. The heating speed is fast, and the thermal inertia is small, which effectively reduces the influence of thermal overshoot on the detection result; The copper block is thicker and larger, the heat capacity is large, and the temperature rises faster after cooling; The life of the heating device is long, and the electric heating tube is located in the middle of the copper block, and the change of cold and heat is small, and it is not easy to be damaged.
Cooling is achieved by: The ambient air is converted into a high-pressure airflow by the air pump through the 1-4 nozzles, and the copper plate is locally cooled rapidly. As shown in the dotted line in Figure 3, the temperature of the temperature sensitive part is lowered and the thermostat is reset. This approach has three distinct advantages:
First, the cooling rate changes with the pressure of the airflow, and the cooling air pressure is continuously adjustable in the range of 0-1 MPa, so that the on-off time can be controlled. Can meet the standard requirements or the manufacturer's own declared test requirements;
Secondly, according to the size of the sensitive components of the temperature controller to be tested, it is possible to flexibly select one or four nozzles to apply the copper blocks around the sensitive components of the temperature controller. The local cooling of the surface of the copper block around the temperature sensitive component is achieved, and the temperature of the entire thermostat is not required to be lowered, and the on-off speed can be adjusted in a larger range;
Third, the device under test is fixed on the copper plate, which is closest to the actual working condition of the thermostat.