First. Maintenance of electrical parts

1. The circuit system shall be cleaned at least once every four months to prevent dust in the air from attaching to the cold parts of the machine, especially the condenser, evaporator and other accessories.

2. The distribution board shall be cleaned and maintained regularly. Dust will affect the heat dissipation and electrical insulation of components; Loosening of contact connectors of components and parts will put the whole equipment in dangerous working condition, which may burn the components or cause fire. When cleaning the distribution board, use a vacuum cleaner to remove the dust from the distribution board. After the component contact connector is repaired, use the matching tool to lock it.

3. Observe whether the high-current contactor and circuit breaker (control compressor and fan) have discoloration and scorch marks, and replace them in time if any.

Second. Maintenance of waterways and refrigeration units

1. The radiator (condenser) of the refrigeration unit should be regularly maintained and kept clean. The dust sticking to the condenser will cause the poor heat dissipation of the compressor to cause the high pressure switch to trip and cause the false alarm. The condenser should be maintained regularly every month. Use a vacuum cleaner to remove the dust attached to the condenser's heat dissipation mesh, or use a hard brush after starting up, or use a high pressure nozzle to blow the dust away.

2. The refrigeration system is the core of the thermal shock chambers. Every year, all copper pipes must be inspected to see if there is any leakage of snow, and all horn joints and welding joints must be treated immediately if there is any leakage of oil. Please patrol the copper pipe, each horn joint and welding joint once a month. If there is any abnormality, please notify Keming or directly find professional personnel to deal with it.

3. When the equipment is not used for a long time, the compressor should be started once every two weeks, and the power-on time should not be less than 1 hour.

4. Waterway system: please check regularly (at least once a month) to ensure that there is no water leakage or blockage in the pipeline, and the water level of each water level control cup is free of leakage and normal. Regularly clean the dirt or sediment in the pipeline and water level control cup, and strictly use the water source that meets the water quality requirements, which is conducive to ensuring the smoothness of the water system for a long time.

5. For dry and wet ball type test chamber, it is necessary to check the dry and wet ball gauze frequently. When the gauze becomes hard or dirty, it should be replaced in time. It is recommended to replace it once every three months.

6. The water storage in the humidifier should be replaced once a month to ensure clean water quality and smooth water flow.

Third. Box maintenance and cleaning

1. Box cleaning: The inside of the box should be cleaned at least once every half a year. When cleaning, please use a vacuum cleaner to remove dust or use compressed air to blow dust.

The outer box needs to be cleaned once a month. When cleaning, it can be wiped with anti-rust oil. Do not use corrosive liquid.

2. Regularly check whether the two gas-type temperature protection switches in the high and low temperature cabin are invalid, and the temperature setting value is the factory value by default. By trying to manually adjust to the current studio temperature value, the machine will give an alarm under normal conditions, indicating that the temperature protection switch is effective.

3. After each test and use of the equipment, the possible residual sundries in the working room should be removed in time to keep the working room clean, so as to prevent the sundries from polluting the working room after being inhaled by the air duct.

Fourth.Precautions for operation

1. Try to avoid frequent start and stop of the thermal shock chambers (try not to start the operation again within five minutes after the thermal shock chambers stops), so as not to increase the mechanical load of the refrigeration system compressor and affect the service life of the unit.

2. It is strictly forbidden to test flammable, explosive, volatile and corrosive substances in the thermal shock chambers, otherwise it will cause accidents and cause machine damage or test result failure.

3. The placement of the test object shall not affect the balance and smoothness of the air flow in the workshop, otherwise it will affect the performance of the impact box and the authenticity of the test. On any section perpendicular to the wind direction of the internal circulation airflow, the total area of the test object shall not be greater than 1/3 of the sectional area of the workroom in that direction.

4. Before the operation of the thermal shock chambers, the door of the test chamber should be closed and closed tightly, otherwise the chamber gas will leak out and the test will not meet the performance requirements.

5. The hot and cold shock box should be operated by professional personnel to avoid unnecessary damage due to improper operation.

6. If the thermal shock chambers operates under low temperature conditions below 0 ℃, try to avoid opening the door of the test box, because opening the door can easily cause frost in the evaporator and other parts of the refrigeration system during the low temperature test, especially when the lower the test temperature is, the more serious the situation is. If the door must be opened, try to shorten the opening time.

7. After the thermal shock chambers is used to complete the low temperature test run, it is necessary to set the test temperature condition to 30 ℃ for drying treatment for about half an hour (return to normal temperature, the temperature controller can set this automatic function), and then shut down and open the door of the test box to take and place the test article, so as not to affect the test performance of the next operation condition. If the drying treatment at 30 ℃ is not carried out, the machine will fail.

8. When the thermal shock chambers operates at high temperature and high humidity, it is forbidden to open the box door, otherwise the following adverse consequences may be caused:

• The high temperature gas rushed out of the test chamber, which is easy to cause personal burns.
• The inside of the box door, the test area and the surface of the test material still maintain a high temperature, which is easy to burn the hands.
• High temperature air may trigger the fire alarm and cause misoperation.

The opening operation of the thermal shock chambers door: the operator must move backward along the opening direction through the test box door to prevent a large amount of hot gas from gushing out of the test box and hurting people just after the high temperature test.

9. During the operation of the thermal shock chambers, do not touch and check the machine system components with your hands to avoid electric shock or motor stranding accidents; Therefore, please stop the machine and turn off the power before checking.

The frost source of the thermal shock chambers

The frost in the thermal shock chambers grows on the energy storage components in the precooling zone. We know that the gas flow and moisture of the thermal shock chambers are output through specific channels. During the test operation, the equipment box is in a sealed state, thus forming a closed loop of sealing. When the equipment is simulating the cold and hot environment, the temperature and humidity will change, resulting in the condensation of water vapor after freezing, forming frost or crystallization.

Frosting during the test may cause some bad consequences. If the equipment frosts for a long time, it may also increase the operating burden of the refrigeration compressor, significantly reduce its cooling effect, and even directly affect the reliability of the test results. Therefore, once frost is found on the equipment, it is necessary to deal with the cause in time.

The defrosting method of the thermal shock chambers

Now many experimental equipment have the function of defrosting. Its main principle is to defrost automatically through the low temperature chamber, and then install and change automatically through the solenoid valve. The high temperature and high pressure at the exhaust end of the compressor are introduced into the refrigeration evaporator. The surface temperature of the evaporator is increased by absorbing heat energy, and the frost is turned into water. Then the water is discharged from the test chamber through a fixed channel, so as to achieve the purpose of equipment defrosting.

In general, there are two defrosting methods for the thermal shock chambers. One is to set the time, and the other is to set the cycle time. Most manufacturers and customers rarely use the set time to defrost, because its disadvantage is that the equipment may still be running after the set defrost time is over. During the test, the cycle time is defrosted after the thermal shock test, so it is recommended to set it according to the cycle time.

All cold cycle and thermal cycle impact test rooms have set the defrosting frequency before leaving the factory, such as once every 20 cycles or once every 20 hours. When the number of cycles is reached, defrosting will be automatically performed. Users do not need to modify according to the recommended value. If the customer has his own defrost frequency requirements, the cycle number or time can be modified in the defrost setting of the equipment control system. The range of settable values can be set from 1 to 9999 hours according to the time and from 1 to 9999 times according to the cycle time.

In addition, we try to reduce the opening times of the box door during the operation of the equipment to avoid increasing the frost body of the equipment. Defrosting is one of the common problems in the daily use of the thermal shock chambers. In most cases, you can deal with it by yourself through troubleshooting. You should try to master the method to deal with this situation, so as to better maintain the equipment in the future. If there are any technical problems in the daily operation of the test equipment, you can also contact the after-sales personnel of the manufacturer of Keming directly for communication and handling.

First. Experimental principle

1. Constant damp heat test

The constant damp heat test is the damp heat test in which the temperature and humidity test conditions do not change with time. The moisture effect of the product is mainly caused by the three physical phenomena of water vapor adsorption, absorption and diffusion. The constant damp heat test method can be selected when the ambient temperature of the testing place where the product is used does not change much and condensation does not occur on the product surface.

The simultaneous action of high temperature and high humidity will accelerate the corrosion of metal parts and the aging of insulating materials. For semiconductor devices, if water vapor penetrates into the die, it will also cause changes in electrical parameters. Especially at the bond or connection of two different metal materials, the infiltration of water vapor will produce an electrochemical reaction, which greatly accelerates the corrosion rate.

In a hot and humid environment, the electroplating layer of the tube shell may peel off, and the outer lead may also be rusted or broken. Therefore, the environmental conditions of high temperature and high humidity are one of the important tests for evaluating the stability and reliability of devices.

2. Alternating damp heat test

Alternating damp heat test method, that is, a damp heat test in which the temperature and humidity conditions periodically fluctuate between high temperature and high humidity and low temperature and high humidity within 24 hours.

When the test sample is under alternating high-humidity and high-temperature conditions, water vapor is sucked into the device through diffusion, thermal movement, respiration and capillary phenomena by virtue of temperature. On the one hand, its intake is related to temperature, absolute humidity, and time (the higher the temperature, the greater the kinetic energy of water molecules, and the easier it is for water molecules to enter the interior of the device. The greater the absolute humidity, the more water molecules are contained, and the water molecules penetrate into the interior of the device more likely).

On the other hand, it is related to the temperature change rate and temperature difference (the temperature change rate determines the number of "breathing" per unit time; the temperature difference determines the degree of "breathing"). The alternating action of high temperature and high humidity at the same time will accelerate the corrosion of metal parts and the aging of insulating materials.

The alternating damp heat test is different from the constant damp heat test. It uses temperature cycling to improve the test effect. The purpose is to provide an alternating process of condensation and drying, so that the water vapor entering the sealed enclosure can have a "breathing" effect, thereby accelerating the corrosion process. At high temperatures, the effect of moisture will be more pronounced.

The test included a low-temperature subcycle, which accelerated degradation that would not otherwise be apparent. This degradation can be revealed by measuring the electrical properties (breakdown voltage and insulation resistance) or by performing a sealing test. If necessary, the alternating damp heat test can also apply a certain electrical load to some components to determine the electrochemical corrosion resistance of current-carrying components, especially thin wires and contacts.

Second. How to choose the type of damp heat test

1. Select the damp heat test method according to the characteristics of the sample itself. The test sample is solid or insulating, and the constant damp heat test is usually used to test the electrical or insulating properties of the product in a humid atmosphere; if the test sample is sealed or hollow, the alternating damp heat test is often used because the sample will Thermal expansion and contraction under the action of thermal stress cause the product to be damp.

2. Select the damp heat test method according to the moisture mechanism of the sample. If the sample is damp after absorbing or absorbing moisture, the constant damp heat test should generally be used; if the sample is condensed or through respiration to strengthen the influence of humidity on the product, the alternating damp heat test should be used.

First. Anti-condensation analysis of temperature chamber

In environmental stress screening, the root cause of condensation on the surface of the tested product is that the temperature of the surface of the tested product is lower than the dew point of the air in the temperature chamber. Therefore, there are several possible ways to prevent condensation on the surface of the tested product:

1. Improve the circulation of the gas in the chamber, so that the temperature of the tested product in the temperature chamber is always synchronized with the temperature change of the gas in the chamber, and the difference between the temperature of the tested product and the temperature of the gas in the chamber is very small, which is not enough to make the temperature of the tested product Condensation appears on the surface of the sample.

2. Take appropriate measures to make the rising rate of the dew point of the gas in the chamber lag behind the temperature rising rate of the surface of the tested product, so that the dew point of the gas in the chamber is always lower than the temperature of the surface of the tested product, so as to prevent condensation on the surface of the tested product Phenomenon.

3. Control the absolute humidity of the gas in the chamber so that the dew point of the gas in the chamber is always lower than the lower limit temperature of the gas in the chamber, so as to avoid condensation on the surface of the tested product.

Among the above control methods, methods 2 and 3 have certain feasibility. When we try to reduce the absolute humidity of the gas in the chamber, we can effectively reduce the dew point of the gas in the chamber to ensure that the temperature of the tested product is higher than that in the chamber. The dew point of the gas prevents condensation on the surface of the tested product.

Second. KOMEG Solution to Condensation

After long-term observation of environmental stress screening test, KOMEG professionals found that the factors affecting the change of gas dew point in the constant temperature and humidity test chamber mainly include the following two points:

1. Ambient humidity: When the ambient operating humidity of the test chamber is relatively high, condensation is likely to occur in the chamber.

2. Tightness of the chamber: the better the tightness of the chamber, the less the influence of environmental humidity on the gas in the chamber.

Environmental humidity is an uncontrollable factor. Due to the needs of work or engineering reasons, it is difficult to achieve absolute sealing of the chamber. Gas exchange is inevitable inside and outside the general constant temperature and humidity test chamber, which is the difficulty of the general constant temperature and humidity test chamber in preventing condensation.

In order to overcome the influence of environmental humidity on the dew point of the gas in the chamber through the gap of the chamber, KOMEG at this stage adopts the method of supplementing dry air in the chamber to make the air pressure inside the chamber greater than that outside the chamber, prevent the water vapor outside the chamber from entering the chamber, and control the humidity inside the chamber, so as to ensure that the dew point of the gas in the chamber is lower than the surface temperature of the tested object, eliminate the basic conditions for condensation, better solve the problem of condensation of the tested object, and avoid condensation for customers, Provides reliability solutions.

Finally, we summarize several conclusions and suggestions:

1. A small amount of condensation during the environmental experiment will not damage the performance of the equipment, nor affect the analysis of the experimental results.

2. In order to prevent the generation of a large amount of condensation and cause wrong guidance to the analysis of the experimental results, the products are generally preheated in advance during the environmental experiment.

3. The environmental experiment has a great impact on the experimental samples, which may change the mechanical, physical and electrical properties of materials. Therefore, in the early stage of product design, considering the actual use conditions, select appropriate components and parts, and adopt derating design, redundancy design, tolerance design, climate and environmental protection design, cushioning and vibration reduction design, thermal design and other means to effectively improve the reliability of products. In the environmental experiment, only by applying appropriate experimental conditions, exposing existing problems and seeking appropriate improvement measures, can the adaptability of the product be further determined to make the product meet the use requirements.

Regarding the winter maintenance measures for high and low temperature chamberes, we mainly focus on the following four aspects: selection measures, thermal insulation measures, heat tracing measures, and maintenance measures.

1. Model Selection

Select the instrument with thermal insulation device. According to the type and purpose of the instrument and the geographical location to be installed, put forward the requirements for thermal insulation and antifreeze of the instrument, and then submit it to the manufacturer for treatment. In some places in the north, the temperature difference between day and night is too large, and it can reach more than - 20 degrees at night.

2. Thermal insulation measures

Thermal insulation materials shall be used for insulation, that is, thermal insulation materials shall be used to wrap the parts of the instrument that are easy to freeze or are afraid of freezing. When winter comes, check and drain frequently to prevent damage of packaged insulation materials.

3. Heat tracing measures

The steam tracing measure is to use pipe steam heating for insulation. The steam does not need to be too hot. The heat preservation steam volume can be adjusted according to the weather temperature changes. If the temperature is too high or too low, the condensate in the transmitter impulse pipe will vaporize and affect the transmitter operation. At the same time, check whether the steam insulation pipeline is unblocked or blocked before steam transmission in winter.

Secondly, electric heating belt measures are taken: electric heat tracing insulation technology is a new heating technology that directly converts electric energy into heat energy. Add thermal insulation cable, wind the tracing band on the instrument or stick it inside the instrument cabinet.

4. Maintenance measures

① The installation site shall be reasonably selected for installation measures: dry place without rain and snow leakage.

② If conditions permit, special personnel shall be assigned to conduct technical confirmation and disposal on whether the insulation materials are damaged and whether the steam pipeline is blocked every day.

③ Alarm measures If conditions permit, small audible and visual alarm devices in the state of steam leakage or power failure can be installed to facilitate the discovery and timely treatment of hidden dangers of thermal insulation and antifreeze measures.

④ Patrol inspection measures shall be regularly carried out by the person in charge of regional instrument maintenance according to the scheduled patrol route. During the patrol inspection, check whether the insulation pipeline valve is normal, whether the insulation chamber is normal, whether the drainage device is normal, whether the insulation material package is intact, and whether the electric tracing power supply components are normal. Focus on the inspection of the instruments of the devices that are easy to freeze, make the inspection records, carry out the dry, complete and clean maintenance of the instruments and their thermal insulation and antifreeze measures, and timely solve the thermal insulation and heat tracing problems that occur on the site.

⑤ Prevent the water from circulating due to icing.

a. Use high-purity refrigerant. If the refrigerant is filled with too much water, it will cause ice blockage.

b. Check whether the drying filter is aging. If it is aging, replace it in time, otherwise it will lose its proper drying and water absorption function and cause icing.

c. Check and maintain the water storage in the humidifier should be replaced once a month to ensure clean water quality. The humidification water tray should be cleaned at least once a month to ensure smooth water flow.

At the same time, it is dry and dry in winter. The circuit control system and some components of the test equipment are easily affected by static electricity, which may affect the test results, or cause static breakdown and make the equipment unable to operate. During the normal maintenance of the test chamber, you should also pay attention to taking anti-static measures for your equipment to reduce the occurrence of static electricity. The following methods can be referred to:

1. Maintain the humidity of the environment of the test chamber: generally, static electricity is caused by the drying of the component surface. Increasing the humidity of the laboratory environment can reduce the probability of static electricity. When increasing the ambient humidity, pay attention to that the humidity should be within the specified range.

2. Hand washing is required before operating the equipment. If the staff directly operate the equipment with dry hands, static electricity may be caused. In addition, operators can also wear anti-static bracelets to avoid static electricity.

3. Ensure that the equipment is well grounded. This is because when the equipment is running, there will be friction in one way or another. The friction process may produce static electricity. When the equipment is well grounded, even if there is a small amount of static electricity, it will quickly disappear through the ground wire.

If the dust on the circuit of the test chamber is not cleared, a large area of electrostatic breakdown will occur and cause a fault in case of static electricity. Therefore, we hope that you can avoid the occurrence of static electricity through the above methods. At the same time, the maintenance of the equipment should be continued to avoid a large amount of dust adhering to the equipment and components.

In addition to static protection in winter, the test equipment should also pay attention to the impact of low ambient temperature on equipment and components, and take preventive measures as early as possible. Only by protecting the test chamber equipment from all aspects can we accept the test of cold winter and facilitate our reliability testing.