Definition
The hot, cold, damp, and hot test chamber is a closed experimental equipment that simulates the temperature and humidity conditions of the environment, which can produce an environment of alternating cycles of high temperature, low temperature and humidity and heat in a controlled space. Its core function is to replicate the temperature and humidity changes that materials or products may encounter during actual use, transportation or storage, with a particular focus on the effect of temperature sudden changes and humidity coupling effects on the performance of specimens. This type of equipment is widely used in electronic and electrical engineering, aerospace, automobile manufacturing, plastic chemicals, coatings and building materials, etc., to evaluate the environmental adaptability, reliability and durability of products, but do not involve medical or drug-related tests.
How it works:
The hot, cold, damp, and hot test chambers operate based on the basic principles of thermodynamics and heat transfer. Its temperature and humidity control system is composed of refrigeration circuit, heating circuit, humidification circuit and air circulation system. The refrigeration part usually adopts the compressor cooling method, which cools down by absorbing the air heat in the box in the evaporator. The heating part relies on a resistive heating element to provide heat. Humidity control is controlled by an evaporative humidifier or steam humidifier, which converts deionized water into water vapor and is injected into the chamber, which is regulated by feedback from a humidity sensor. The air circulation system uses a fan to drive the air in the box to flow through the heater, refrigeration evaporator and humidifier to ensure the uniform distribution of the temperature and humidity field. The system dynamically adjusts the working state of each actuator according to the preset temperature and humidity curves through a programmable logic controller or microcomputer processor to complete the alternating hot and cold or constant humidity and heat test.
Measurement method
The performance of the test chamber is mainly characterized by parameters such as temperature range, temperature change rate, temperature uniformity, humidity range and humidity fluctuation. The temperature range is typically -70°C to +150°C or wider; The temperature change rate refers to the amplitude of temperature change per unit time, and the commonly used unit is °C/minute; Temperature uniformity refers to the difference in temperature between different measurement points; The humidity range generally ranges from 20% relative humidity to 98% relative humidity. The measurement method follows the national standard. Temperature measurement uses platinum resistance temperature sensor or thermocouple, and the distribution method is placed according to the volume of the box according to the position specified in the standard, and if necessary, additional measurement points are added on the surface or inside of the specimen. Humidity measurement uses the dry and wet bulb method or capacitive humidity sensor, and the dry and wet bulb method obtains the relative humidity value by calculating the temperature difference between the dry bulb and the wet bulb. All sensors are calibrated regularly to ensure that data is traced back to national standards.
Influencing factors
The accuracy and reproducibility of the test results are constrained by many factors. The box structure and thermal insulation performance directly affect the temperature stability, and the poor sealing or aging of the insulation layer will lead to heat loss, causing the actual temperature to deviate from the set value. Air flow distribution is critical to temperature uniformity, and improper airflow design can create temperature dead zones in the box. The load and heat capacity characteristics of the specimen cannot be ignored, and a large number or high specific heat capacity of the specimen will significantly prolong the temperature control equilibrium time, especially in the stage of rapid temperature change, the loading effect may cause the actual specimen surface temperature to lag behind the air temperature in the box. During the humidity control process, the water quality of the evaporated water source, the fluctuation of water supply pressure and the scaling of the humidifier will interfere with the accuracy of humidity output. In addition, the basic ambient temperature and relative humidity of the environmental laboratory will also affect the cooling efficiency and humidity regulation ability of the test chamber.
Applications:
Hot and cold, damp and hot test chambers are responsible for environmental adaptability verification in many non-medical industries. In the electronics and electrical industry, it is often used to evaluate whether components such as circuit boards, connectors, and displays have deteriorated insulation properties, metal corrosion, or plastic embrittlement in high, low, low, and high humidity environments. In the field of automobile manufacturing, for interior and exterior trims, rubber seals, sensors and control modules, through cold and hot shock and damp heat cycle tests, the thermal stress and humidity invasion of vehicles when driving in different climatic regions are simulated. The aerospace field uses this equipment to test the functional integrity of avionics and composite structural parts in freezing, condensation, and high altitude and low temperature environments. In the coatings and plasticizers industry, the long-term decay trend of coating adhesion, impact strength and UV resistance of plastics is predicted by damp heat aging tests. Typical test procedures include steady-state high temperature and high humidity test, temperature change cycle test and condensation test.
Key points of selection
When selecting, it is necessary to consider the test standards and the characteristics of the specimen. First, clarify the temperature range and humidity range required for the test, including the minimum temperature, maximum temperature, and whether low temperature and low humidity or high temperature and high humidity conditions are required. Secondly, confirm the requirements of the temperature change rate, the conventional rate is between 1°C/min and 15°C/min, and when a higher change rate is required in special scenarios, a system with greater cooling and heating capacity should be selected. The volume of the box should be greater than 3 to 5 times the total volume of the specimen to ensure air circulation and reduce the load effect. The internal structure needs to consider whether it is equipped with an observation window, test lead holes, sample holder and sample power supply interface. In terms of control system selection, attention should be paid to the flexibility of program editing, data logging functions, and the compatibility of remote communication interfaces. At the same time, the refrigeration and cooling methods were evaluated, and the water-cooled type was better than the air-cooled type in terms of heat dissipation efficiency, but it was limited by the cooling water supply conditions. Finally, the energy efficiency, noise level, and ease of maintenance of the equipment should also be considered to meet the requirements of the laboratory for long-term stable operation.
Use and maintenance
Correct operation and regular maintenance are the prerequisites for ensuring the long-term reliable operation of the equipment. Before use, it should be confirmed that the power supply voltage, cooling water source and drainage system are normal, and it is strictly forbidden to start the humidification system when there is no deionized water to prevent dry burning. Specimens should be placed with sufficient clearance to avoid obstructing the air outlet or air inlet, and to avoid direct exposure of corrosive substances to the box. The box door should not be opened at will during the test, so as not to damage the temperature and humidity field and cause safety accidents or affect the test results. Routine maintenance points include: checking and cleaning the air filter weekly; Clean the condenser cooling fins monthly for dust; The humidifying water tray should be descaled regularly, and it is recommended to use demineralized or distilled water; calibrate temperature and humidity sensors quarterly; Every year, professional and technical personnel are invited to detect leaks, supplement refrigerant and test the performance of the whole machine on the refrigeration system. If abnormal noise, temperature loss of control or humidity cannot be stable, the test should be stopped immediately and the fault should be investigated, and the operation should not be carried out with illness.
Standard system and compliance reference
The design, manufacture and test methods of hot, cold, damp and hot test chambers follow a multi-level standard system. At the international level, the International Electrotechnical Commission standards such as IEC 60068 specify common methods and severity levels for environmental testing, including temperature tests, humidity heat tests, and temperature change tests. In China's national standard system, the GB/T 2423 series is equivalent to adopting the IEC standard, which stipulates in detail the procedures and acceptance requirements for environmental testing of electrical and electronic products. In addition, US military standards and German industrial standards also provide reference for specific industries. Before leaving the factory, equipment manufacturers need to conduct type tests according to relevant standards and issue performance measurement certificates including temperature uniformity, temperature fluctuation and humidity deviation. When formulating internal test specifications, users should combine the test procedures and tolerance levels in the above standards to ensure that the test results are comparable and traceable. Choosing standard-compliant equipment and calibration services can help improve the overall reliability of your lab's quality system.