High and Low Temperature Test Chamber Requirements Specified in the Standard

The test chamber requirements formulated according to relevant standards should meet the following two points:

1. The temperature and humidity in the high and low temperature test chamber are monitored by the sensor installed in the working space. For the test of the heat dissipation test sample, the installation position of the sensor is formulated in the GB/T2421-1999 standard.

2, The temperature and relative humidity of the working space are required to be constant within the nominal value and its specified tolerance range, and the influence of the test sample should also be considered during the test.

Heat dissipation test sample test:

The volume of the high and low temperature test chamber should be at least 5 times the total volume of the test sample, the distance between the test sample and the internal wall of the test chamber should be selected according to the provisions of GB/T2423.2-2001 Appendix A (standard appendix), the wind speed in the chamber should not exceed 1M/S, and the structure of the mounting frame or support frame of the test chamber sample should simulate the real conditions in use as much as possible. Or otherwise, the effect of the sample mounting rack on the exchange of heat and moisture between the test sample and the surrounding space should be reduced to a minimum, and the relevant specifications may also specify dedicated mounting racks.

Test severity level:

The severity grade of the test chamber consists of the test temperature, relative humidity and test time, and is specified by the relevant specifications. The combination of temperature and relative humidity can be selected from the following values:

a, 30℃±2℃ 93%±3%

b, 30℃±2℃ 85%±3%

c, 40℃±2℃ 93%±3%

d, 40℃±2℃ 85%±3%

During the test, the test chamber shall be at the temperature and humidity of the laboratory, and the test sample at the ambient temperature of the laboratory shall be placed in the normal position or other specified position in the laboratory in an unpacked, unenergized, "ready for use" state, under certain circumstances (e.g. The relevant specifications may allow the test sample to be directly sent into the test chamber under the treated test conditions, but the test sample must be prevented from producing condensation, the temperature in the test chamber should be adjusted to a predetermined severity level, the time should ensure that the test sample reaches temperature stability, the test time should be calculated from the specified conditions, if the relevant specifications require, the test sample can be energized or worked in the conditional test phase, and the relevant specifications should specify the working conditions and working time or cycle of the test sample during the test. At the end of the conditional test, the test sample should still be left in the test chamber and the chamber should be adjusted to the standard atmospheric conditions of the test. The relative humidity should be reduced first, and the time should not exceed 2 hours. The temperature change rate in the test chamber should not exceed 1℃/min on average within 5min, and the relative humidity during temperature regulation should not exceed 75%. After the conditional test, the test sample should enter the recovery procedure.

High and Low Temperature Test Standard for PC Plastic Material 

First, high temperature test

After being placed at 80±2°C for 4 hours and at normal temperature for 2 hours, the dimensions, insulation resistance, voltage resistance, key function, and loop resistance should meet normal requirements, and the appearance should not be deformed, warped, or degumming. Key bumps collapsing at high temperatures and reduced pressing force are not evaluated.

Second, low temperature test

After being placed at -30±2℃ for 4 hours and at normal temperature for 2 hours, the dimensions, insulation resistance, voltage resistance, key function, and loop resistance should meet normal requirements, and the appearance should not be deformed, warped, or degumming. 

Third, temperature cycling test

After being placed in 70±2℃ for 30 minutes, remove at room temperature for 5 minutes; then after being placed in -20±2℃ for 30 minutes, remove at room temperature for 5 minutes. After such 5 cycles, the dimensions, insulation resistance, voltage resistance, key function, and loop resistance should meet normal requirements, and the appearance should not be deformed, warped, or degumming. Key bumps collapsing at high temperatures and reduced pressing force are not evaluated.

Fourth, heat resistance

After being placed in an environment with a temperature of 40±2℃ and a relative humidity of 93±2%RH for 48 hours, the dimensions, insulation resistance, voltage resistance, key function, and loop resistance should meet normal requirements, and the appearance should not be deformed, warped, or degumming. Key bumps collapsing at high temperatures and reduced pressing force are not evaluated.

High Pressure Failure Caused by Water Cooling Unit of High and Low Temperature Test Chamber

1, High and low temperature test chamber refrigerant charging too much. Such a thing is usually produced after the overhaul, mainly manifested as the suction and exhaust pipe working pressure, balanced working pressure are high, refrigeration compressor operation current is also high.

Solution: Air should be released under the rated load according to the working pressure and balanced working pressure of the suction and exhaust pipe and its operating current until normal.

2, The water cooling temperature of the high and low temperature test chamber is too high, and the actual condensation effect is poor. The cooling water rated load of the refrigeration unit is 40~45'C, the temperature is high, and the heat pipe is not good at heat dissipation, which must cause high condensing pressure, and this phenomenon is therefore generated in the high temperature season.

Solution: The reason for the high temperature will be: the common faults of the closed cooling tower, such as the centrifugal fan is not turned on so that the water distributor does not turn, mainly manifested in the high temperature of the cooling circulating water and the rapid rise; The average external temperature is high, the waterway is short, and the water flow of the circulating system is small, so the cooling circulating water temperature is usually maintained at a high level, and the method of upgrading the storage pool can be treated.

3, The water cooling of the high and low temperature test chamber is not enough, and the water yield cannot reach the rated value. The specific performance is that the difference of water pressure in and out of the generator set is reduced (compared with the pressure difference at the beginning of the operation of the system software fund), and the temperature difference is increased.

Solution: The reason for the insufficient water output is that the system software has less water or gas. The solution is to install an automatic exhaust valve in the upper air of the pipeline to develop the exhaust pipe; The pipeline filter is blocked or used too thin, the water permeability working capacity is limited, should use a suitable filter device and clear the q filter screen every quarter; The centrifugal pump is small and does not match the system software.

4, High and low temperature test chamber cooler fouling or blocking. Condensate water is usually used in drinking water, at about 40°C is very easy to accumulate scale, and because the closed cooling tower is vertical, it is immediately exposed to the gas, dirt and dirty things are very easy to enter the cooling system, resulting in the cooler dirty blocked, the total heat transfer area is small, low efficiency, and also harm the water output. Its main performance is that the generator set inlet and outlet water pressure difference, the temperature difference increases, the temperature of the hand cooler is very high, and the copper pipe of the cooler exhaust air conditioning is hot.

Solution: Reverse cleaning of the generator set should be carried out every quarter, and chemical cleaning scale cleaning should be carried out if necessary.

How to Change the Refrigerant Oil of Thermal Shock Test Chamber?

Thermal shock test chamber is a necessary test equipment for metal, plastic, rubber, electronics and other material industries, used to test material structure or composite materials, in an instant under the continuous environment of extremely high temperature and extremely low temperature to endure the degree of chemical changes or physical damage caused by thermal expansion and contraction of the sample in the shortest time. Thermal shock test chamberr meets the test method: GB/T2423.1.2, GB/T10592-2008, GJB150.3 thermal shock test.

In thermal shock test chamber, if the compressor is semi-closed piston compressor in operation for 500 hours, it is necessary to observe the oil temperature and oil pressure changes of the frozen oil, and if the frozen oil is discolored, it must be replaced. After the initial operation of the compressor unit for 2000 hours, the cumulative operation of three years or the operation time of more than 10,000 to 12,000 hours should be maintained within a time limit and the chilled oil should be replaced.

The refrigerated oil replacement of the semi-closed piston compressor in thermal shock test chamber can be performed according to the following steps:

1, Close high pressure exhaust and low pressure suction stop valve of thermal shock test chamber, and then screw down the oil plug, the oil plug is generally in the bottom of the crankcase, and then put the frozen oil clean and clean the filter.

2, Use the low-pressure impact gas valve needle to blow nitrogen into the oil port and then use the pressure to discharge the residual oil in the body, install a clean filter and tighten the oil plug.

3. Connect the low pressure tube filled with fluorine gauge to the low pressure process valve needle with a vacuum pump to pump the crankcase into negative pressure, and then remove the other fluorine tube separately, put one end into the chilled oil, and put the other end on the valve needle of the low pressure suction of the oil pump. The chilled oil is sucked into the crankcase due to the negative pressure, and add it to the position slightly higher than the lower limit of the oil mirror line.

4. After injection, tighten the process column or remove the fluorine filling tube, and then connect the fluorine pressure gauge to vacuum the compressor.

5. After vacuuming, it is necessary to open the high and low pressure stop valve of the compressor to check whether the refrigerant has leaked.

6, Open thermal shock test chamber unit to check the lubrication of the compressor and the oil level of the oil mirror, the oil level can not be less than a quarter of the mirror.

The above is how to replace the refrigerant oil of the semi-closed piston compressor in thermal shock test chamber. Because the refrigerant oil has hygroscope, the replacement process needs to reduce the air entering the system and the oil storage container. If the cold aging oil is injected too much, there is the risk of liquid shock.

How to Control the Uniformity of Temperature and Humidity When the High and Low Temperature Test Chamber is Loaded?

High and low temperature test chamber "load" refers to the weight of our test product, or the product needs to be energized to test its heat is referred to the load. The "load" in the high and low temperature chamber is divided into non-heating load and heating load, and the test product that is not powered on or powered on is called non-heating load. This load has no effect on the temperature and humidity range of the constant temperature and humidity test chamber as a whole, but only affects the time of rising and cooling or rising and falling humidity. The test product that needs to be powered on and emits heat is a heating load, which has a relatively large impact on temperature and humidity, and the load that different temperature points or humidity points can withstand is not the same.

It is very important to select the appropriate test equipment when the product is undergoing temperature test.

1, The test range must be required to meet the product failure possibility test range, that is, whether it is a high temperature chamber or a low temperature chamber or a temperature and humidity test chamber or a thermal shock test chamber should be able to meet the extreme temperature conditions specified in the test requirements.

2, Ensure the volume of the test sample, it should not be greater than the working volume of the test equipment 1/5 of the principle standard to select the test equipment.

3, In order to ensure the uniformity of temperature in the test area, the convection mode of the test chamber is customized according to the heating power of the sample. The natural convection of hot air is used, which is especially suitable for drying powder, and most of the test equipment adopts the forced circulation of hot air. The difference in the temperature distribution of the equipment has a great impact on the test results. When a large sample is used, or the number of samples tested at the same time is large, the test results will vary greatly with the different locations, so the temperature uniformity of the equipment should be selected as best as possible. The uniformity performance of the high and low temperature alternating and humidity test chamber of the macro exhibition instrument can reach ≤0.5°C.

4, To prevent the sample heat absorption or heat release caused by heat radiation or heat load in the test area, the heating or refrigeration system device of the equipment has no effect on the temperature equalization and cooling rate of the sample during the test.

We can not be empty when using the high and low temperature test chamber, we will more or less place the test sample, and the user - generally after the test sample put into the heat is not too much concept, in order to avoid the temperature can not reach, can not fall down or rise and cool slowly this kind of situation, so we recommend that when purchasing equipment, to its heat requirements, or place the material, weight, size of the sample to tell the manufacturer, which will effectively help the test to make the test effect better.

Introduction and Comparison of Thermocouple Temperature Sensing Lines

Instructions:

The background principle of thermocouple is "seebeck effect", also known as the thermoelectric effect, the phenomenon is that when two different metal endpoints are connected to form a closed loop, and if there is a temperature difference between the two endpoints, then there will be current generated between the loops, and the higher temperature contact in the loop is called "hot junction". This point is usually placed at the temperature measurement; The lower end of the temperature is called "cold junction", that is, the output end of the thermocouple, whose output signal is: DC voltage is converted into a digital signal through the A/D converter and converted into the actual temperature value through the softwares algorithm. 

Various electric heating couples and their range of use(ASTM E 230 T/C):

JIS,ANSI(ASTM) thermoelectric coupling appearance identification:

Note:

1.ASTM, ANSI: American standard

2.JIS: Japanese standard

Lighting Installation Position of High and Low Temperature Test Chamber

According to the different needs of users, the installation position of the lamp in the high and low temperature laboratory is different. The constant temperature and humidity test chamber tests the heat resistance, cold resistance, dry resistance and moisture resistance of various materials. Suitable for electronic, electrical, food, vehicle, metal, chemical, building materials and other industries of quality control. This series of products is suitable for aerospace products, information electronic instruments, materials, electrical, electronic products, various electronic components in high and low temperature or temperature and humidity environment, to test its various performance indicators.

The most common temperature test equipment in environmental test equipment, and similar related products are high and low temperature alternating test chamber, constant temperature and humidity test chamber, high and low temperature and humidity alternating test chamber and so on. It is suitable for high temperature and low temperature reliability test of industrial products. Walk-in high and low temperature test chamber, walk-in high and low temperature test chamber is used for thermal test of national defense industry, aerospace industry, automatic components, automotive parts, electronic and electrical parts, plastics, chemical, pharmaceutical industry and related products. It provides large parts, semi-finished products, and large temperature and humidity test environment space for finished products. It is suitable for the test equipment with large quantity and volume.

Some are installed on the interal chamber or door, and some are not installed. Where is the best place to install light bulbs?

In fact, the high and low temperature test chamber lighting has advantages and disadvantages no matter where it is installed.

If the lighting is installed in the broadcast room, you can clearly see the condition of the entire broadcast room and observe the product at any time.

The lamp is installed on the door, and when the user conducts the double 85 test or the high temperature and high humidity test, the humidity is not easy to invade the lamp, and the lamp is not easy to damage, which can greatly reduce the after-sales service fee. However, its observation field is very small, can only observe the near attractions, customers observe the product is not very convenient.

If the lamp is installed on the right side of the internal chamber, it is recommended to be completely sealed to prevent moisture intrusion to ensure the long-term stable operation of the lamp. If it is installed on a door, it is recommended that the viewing window be trapezoid, so that you can have a wider field of view.

Of course, some corporate customers choose not to install lighting when purchasing high and low temperature test chambers to reduce production costs and later management costs. However, customers can not observe products at any time when doing tests, and they can not meet the needs of different customers who want to observe products.

Operation Precautions of Constant Temperature and Humidity Test Chamber

1, In order to avoid machine failure in the constant temperature and humidity test chamber, please provide power supply within the rated voltage range.

2, In order to prevent electric shock or misoperation and failure, do not switch on the power supply before the installation and wiring is finished.

3, This product is a non-explosion-proof product, please do not use the constant temperature and humidity machine in the environment with flammable or explosive gas.

4, Please try not to open the test chamber door during the work of the instrument, open at high temperature may cause hot injury to the operator, open at low temperature may cause freezing injury to the staff, and may cause freezing of the evaporator, affecting the refrigeration effect. If you must open, please do some protective work,

5, It is prohibited to disassemble, process, transform or repair the constant temperature and humidity machine without permission, otherwise there will be abnormal action, electric shock or fire risk.

6, The chamber's ventilation holes should be kept unobstructed to avoid failure, abnormal operation, reduced life and fire.

7. If the machine is damaged or deformed when unpacking, please do not use it.

8, The machine installation and setting should be careful not to let dust, wire, iron filings or other things into, otherwise wrong action or failure will occur.

9, Wiring must be correct, must be grounded. Non-grounding may cause electric shock, misoperation accidents, abnormal display or large measurement errors.

10, Regularly check the terminal screws and fixed frame, please do not use in the case of loose.

11, During the operation of the instrument, the power input terminal cover must be installed on the terminal board to prevent electric shock.

12, The instrument in operation, modify the setting, signal output, start, stop and other operations, should be fully considered before the safety, wrong operation will cause damage to the working equipment or failure.

13, Please use a dry cloth to wipe the instrument, do not use alcohol, gasoline or other organic solvents, do not splash water on the instrument, if the instrument is immersed in water, please stop use immediately, otherwise there is the risk of leakage, electric shock or fire.

14, The internal parts of the instrument have a certain life period, in order to continue to use the instrument safely, please carry out regular maintenance and maintenance. When scrapping this product, please treat it as industrial waste.

15, Before starting to check whether the power supply is stable.

Principles That Operating Constant Temperature and Humidity Test Chamber Should Follow 

Constant temperature and humidity test chamber, also known as constant temperature and humidity test machine, programmable temperature and humidity alternating test chamber, thermostat or constant temperature and humidity chamber, can be used to test various environments and test equipment material performance, this material has heat resistance, cold resistance, dry resistance and humidity resistance. However, when using the constant temperature and humidity test chamber, the correct operation helps to obtain scientific data for the experimenter, so what principles should be followed in the operation of the constant temperature and humidity test chamber?

‎First, in the environmental test, the operator must be familiar with the required test sample performance, test conditions, test procedures and test technology, familiar with the technical performance of the test equipment used, and understand the structure of the equipment, especially familiar with the control ‎ operation and performance. At the same time, read the operation manual of the test equipment carefully to avoid abnormal operation of the test equipment due to operation errors, which may cause damage to the test sample and incorrect test data. ‎

‎Second, in order to ensure the normal operation of the test, appropriate testing equipment should be selected according to the different conditions of the test sample, and a reasonable proportion between the temperature and humidity of the test sample and the effective volume of the laboratory should be maintained. For tests of heated test samples, the volume should not be greater than one-tenth of the effective volume of the test chamber. The volume of the unheated test sample should not exceed one-fifth of the effective volume of the test chamber. ‎

Third, for environmental tests that need to add media to the test, it should be correctly added according to the test requirements. ‎ For example, there are certain requirements for water in temperature and humidity test chambers and the resistance should be reduced. There is a more economical and convenient form of pure water on the market. Its resistance is equivalent to distilled water. ‎

Fourth, wet bulb gauze (wet bulb paper) has certain requirements for use in a temperature and humidity test chamber, and no gauze can be replaced, because the relative humidity reading is the difference between the root distance and temperature and humidity, and strictly speaking, it is also related to the local atmospheric pressure and wind speed at the time. The indicator value of wet-bulb temperature is related to the amount of water absorbed by the gauze and the amount of surface evaporation. These are directly related to the quality of the gauze, so the weather stipulates that the wet ball gauze must be a special "wet ball gauze" woven from linen. Otherwise, it is difficult to ensure the correctness of the wet bulb thermometer value, that is, the correctness of the humidity. In addition, the position of the wet gauze is also clearly specified. Gauze length: 100mm, tightly wrap the sensor probe, probe 25-30mm away from the humidity cup, gauze immersed in the cup to ensure the accuracy of equipment control and humidity. ‎

Fifth, the location of the test sample should be more than 10 cm away from the wall of the chamber, and multiple samples should be placed on the same plane as far as possible. Samples should be placed without blocking air outlets and return vents, and temperature and humidity sensors should be kept at a distance. Make sure the test temperature is correct. ‎

Operating the constant temperature and humidity test chamber ‎ in accordance with the above principles, the correct operation of the test process will greatly improve the level of test data. As long as the above principles are adhered to, it should be said that the temperature and humidity tests can be successfully performed. ‎

Sealing Problems and Solutions of High and Low Temperature Test Chamber

High and low temperature test chamber is based on the natural environment such as high temperature, ultra-low temperature, high and low temperature and low temperature drying in the room during the construction of work, and then carries out high and low temperature test and temperature and humidity aging resistance experiment on the commodity, mainly used for industrial products, such as: electronic and electrical, instrumentation equipment, cars and motorcycles, universities and other manufacturing industries.

Because of high temperature testing, ultra-low temperature testing, high and low temperature test cycle system testing, high and low temperature test and other experimental standards, high and low temperature test chamber in the high temperature standards, such as doing 150 ° C extremity of high temperature and 98% of the ambient humidity conditions, and the pressure difference between inside and outside the laboratory to expand substantially, at this moment, the sealing effect of the test chamber really matters. If the airtightness is not very good, it will cause more serious vapor leakage, affecting the precision and accuracy of the temperature.

What are the factors that cause the sealing problem of the high and low temperature test chamber?

First, the constant temperature and humidity test chamber usually has cable holes and ventilation exhaust holes, and the design scheme is very strict.

If the design scheme and production are not scientific, the gap will be too large, and the sealing of the environmental test chamber will not be good. This punching studio should also remember to plug the suitable specifications of the bottle stopper, rubber stopper, etc., to ensure that the sealing of this punching place is intact.

Second, the problem of sealing rubber strips of high and low temperature test chamber. We usually ignore this problem, feel that the sealing strip is added to the door hinge, and should be very sealable under the inhibition of the door hinge, because the aging of the silicone seal, the selection of hard flexibility is unscientific, and the sealing strip is fixed and not the same, often causing steam leakage. It is also simple to handle, often test its tightness, and find that the embrittlement of the sealing strip must be replaced as soon as possible.

Third, because the general volume of the high and low temperature test chamber is relatively large, the tail door specifications are expanded, and the net weight is very large, and the vertical orientation of the door hinge is offset after the long-term load, and the tail door is shifted and closed. Such problems are usually dealt with according to the modified high-load door hinges and the total number of door hinges.

From the above analysis, it can be seen that the sealing problem of the high and low temperature test chamber has some design problems and some maintenance problems. Therefore, we should strictly follow the equipment maintenance manual for regular maintenance in the use of equipment to ensure the normal operation of equipment and no deviation of technical parameters.