The temperature test chamber is generally composed of working room, adjusting equipment, auxiliary equipment and control system. The regulating system includes heater, evaporator and air supply device, and auxiliary equipment main room refrigeration unit. The control system includes temperature controller, program setter, safety alarm device and so on.
The heater is realized by electric heating of resistance wire or electric heating tube; In addition to the natural heating for the drying oven of high-temperature test without heat dissipation sample, it is generally equipped with air supply device for forced air circulation. The air supply mode is mostly upper side supply and lower side return or full orifice top supply and lower side return, which is very important for the uniformity of the whole test chamber.
Most of the refrigeration methods are mechanical refrigeration, the refrigerator has semi closed or fully closed form, and the cooling circuit also has water cooling or air cooling form. Now the refrigerant is mostly environmental friendly, and the throttling method is capillary or electronic expansion valve, which can improve the accuracy and the life of the circuit, and can work continuously for a long time.
The control system now generally adopts PID mode, so that the heating power can be automatically adjusted and controlled with the deviation between the actual temperature and the set temperature, realizing stepless adjustment and small temperature fluctuation; The display part has also been upgraded from the previous digital display mode to the LCD touch screen mode, which is clear, beautiful and more convenient for operation. In addition, the insulation layer of the equipment adopts glass wool or polyurethane foam layer, with small thermal conductivity and good temperature resistance. Thermocouple, platinum resistance and thermistor are used for temperature detection with high accuracy.
How to choose Temperature Test Chamber？
- It must be required that the test scope should meet the test scope of product failure possibility, that is, the high temperature box or low temperature box or cold and hot impact box should meet the extreme temperature conditions specified in the test requirements.
- The selection of test chamber must follow the principle that the sample volume is not more than 1 / 5 of the working volume of the test chamber.
- In order to ensure the temperature uniformity of the test area, forced air circulation or non forced air circulation mode is selected according to the heat dissipation of the sample. The difference of equipment temperature distribution has great influence on the test results. When larger samples are used or a large number of samples are tested at the same time, the test results of different positions will be very different. Therefore, the equipment with the best temperature uniformity should be selected.
- There are two methods to measure the sample temperature: upwind sensor and downwind sensor. The position and control method of temperature control sensor can be selected, and the appropriate equipment should be selected according to the test requirements.
- In order to prevent the sample from absorbing or releasing heat due to heat radiation or heat conduction in the test area, the heating or cooling system of the equipment shall not affect the sample.
- It is easy to record and display. Automatic counter, indicator light, recording equipment, automatic shutdown and other instruments should be installed during cycle test.
- In order to facilitate the sample placement, the sample holder can be placed or suspended, and the mechanical properties of the sample holder will not change due to the change of high and low temperature.
- Leading holes to lead the test power supply to the equipment workshop.
- There should be protective measures for the damage of samples and the safety of test personnel. For example, it is equipped with observation window and lighting, and alarm devices such as phase failure, water shortage, over temperature protection and operator protection.
- Whether remote monitoring function is needed.
Precautions when using Temperature Test Chamber
- The temperature and humidity deviation will appear in the updraft and downdraft during the bulk sample test, so the sample location should be carefully considered. It should be placed in the center of the working space of the test chamber as far as possible. The samples should not touch and overlap each other, and a certain interval should be left to make the air circulate; Moreover, it should be ensured that the sample is easy to move during the test, and it is easy to replace the sample during the test.
- Check whether there are volatile substances such as oil and gas in the test area and whether there are odorous substances. The test results of such substances must be confirmed in advance.
- Pay attention to confirm the temperature condition of the test sample in the test area.
- In order to keep the temperature in the temperature zone consistent, it is necessary to ensure the minimum fluctuation of the test environment temperature and the power supply of the equipment as far as possible, so as to ensure that the test sample does not produce heat radiation and does not absorb heat, so as to ensure that the temperature in the test zone is stable.
- After the end of the temperature test chamber test, quickly remove the test sample will produce unnecessary stress on the sample, and may get unexpected results. Therefore, the test sample must be cooled to the ambient temperature before it can be taken out.
- The thermal conductivity of the installation and support frame of the test sample should be low to ensure that the test sample and the installation and support frame are in an adiabatic state.
The test content of different products is decided by the test requester, designer and tester. From the point of view of providing test chamber in accordance with the test, a technical specification framework of test chamber is established, according to which the test chamber supplier can provide the specific specifications of the equipment. Every kind of test chamber that can simulate the test environment generally has a measurement system, so it is very easy to use existing equipment and purchase new equipment. Simple test chamber can also be manufactured by oneself, but the cost, reliability of test results, precise control degree and safety factors of continuous operation should be considered.
Environmental test is a process that can add value to products, which can not be ignored. As one of the most basic environmental tests, temperature based environmental test is widely used in many fields, which greatly improves the environmental adaptability and reliability of military and civil products, and directly leads to the improvement of product quality. In this paper, temperature type environmental test chamber are briefly introduced. According to the use requirements, the real purpose of environmental test can be achieved by accurately selecting and using.