High and low temperature test chamberIt is a core equipment for simulating extreme temperature environments and assessing product temperature resistance performance, widely used in industries such as electronics, automotive, aerospace, and materials. The temperature control accuracy, uniformity, and fluctuation directly affect the reliability of the test results, so regular calibration according to specifications is required. This article elaborates on the calibration method of high and low temperature test chambers and key precautions in practical operation.

1、 Calibration Basis and Core Projects

1. Main calibration basis

Calibration must strictly follow national standards, with commonly used criteria including GB/T 10586-2006 "Technical Conditions for Damp Heat Test Chambers", GB/T 11158-2019 "Technical Conditions for High Temperature Test Chambers", GB/T 2423.1-2008 "Environmental Testing for Electrical and Electronic Products Part 2: Test Methods Test A: Low Temperature", and GB/T 2423.2-2008 "Environmental Testing for Electrical and Electronic Products Part 2: Test Methods Test B: High Temperature".

2. Core calibration items

The calibration core revolves around "temperature" related indicators, mainly including three items: ① temperature uniformity: the consistency of temperature at various points in the working space of the test chamber; ② Temperature fluctuation: the range of temperature fluctuations near the set value at any point; ③ Temperature deviation: The difference between the actual temperature at each measurement point and the set temperature. In some scenarios, it is necessary to calibrate the heating rate and cooling rate (if the equipment has a rapid temperature change function).

2、 Preparation before calibration

1. Equipment and appliance inspection

① Confirm that the appearance of the high and low temperature test chamber is undamaged, the door seals are intact without aging or deformation, and the ventilation openings are unobstructed; Connect the power supply, test run the equipment, and check that the temperature control system, fan, and heating/cooling unit are operating normally without any abnormal noise or fault alarms. ② Prepare calibration instruments: Select temperature sensors (such as platinum resistance Pt100) and data acquisition devices that have been verified by higher-level metrology institutions and are within their validity period. The accuracy of the sensors should be 1-2 levels higher than that of the calibrated equipment (recommended resolution ≥ 0.1 ℃); Prepare calibration brackets, wires, and other auxiliary tools.

2. Confirmation of environmental conditions

The calibration environment temperature should be controlled at 23 ℃± 5 ℃, and the relative humidity should be ≤ 85%; There is no strong electromagnetic interference, direct sunlight, or airflow impact (such as direct air conditioning) around, to avoid environmental factors affecting calibration accuracy. Simultaneously record the environmental temperature and humidity for easy traceability of subsequent data.

3. Pre treatment of test chamber

Set the calibration temperature points according to the calibration requirements (usually selecting the upper, lower, and middle points of the commonly used temperature range of the equipment, such as -40 ℃, 0 ℃, 85 ℃, 150 ℃), run the test chamber without load, and maintain a constant temperature at each temperature point for more than 2 hours to ensure that the temperature inside the chamber is initially stable.

3、 Specific calibration methods

1. Temperature sensor layout

Using the "nine point layout method" to arrange sensors (applicable to conventional cube workspaces): with the geometric center of the test box workspace as the center, a total of nine measurement points are arranged at the center positions and geometric centers of the upper, lower, left, right, front and rear six faces. The sensor probe should be fixed on the bracket to avoid direct contact with the box wall, heating tube, and refrigerator (at least 50mm away from the box wall), ensuring that the measurement point can truly reflect the temperature of the workspace. If the workspace size is special (such as narrow and elongated), the number and position of the layout points can be adjusted appropriately to ensure coverage of the entire effective work area.

2. Constant temperature and data acquisition

① Set the target calibration temperature, start the test chamber, and maintain a constant temperature for 30 minutes (ensuring complete temperature stability) after the temperature reaches the set value. ② Start the data acquisition device, set the sampling interval (recommended 10-30 seconds per time), continuously collect no less than 30 sets of data (total collection time ≥ 30 minutes), and synchronously record the temperature values, set temperatures, and collection time of each measurement point. ③ Complete the calibration of all preset temperature points in sequence according to the above process, and collect data independently for each temperature point to avoid cross interference.

3. Data processing and result judgment

① Temperature deviation calculation: The temperature deviation of each measurement point is equal to the average temperature of that point minus the set temperature. The maximum deviation of all measurement points must meet the standard requirements (such as high temperature test chamber ≤ ± 2 ℃, low temperature test chamber ≤ ± 3 ℃, subject to equipment specifications and standards). ② Temperature fluctuation calculation: The difference between the highest and lowest temperatures at any measurement point during the acquisition period, with a fluctuation of ≤± 0.5 ℃ (conventional requirement). ③ Temperature uniformity calculation: The difference between the highest and lowest average temperatures at all measurement points during the collection period should be ≤ 2 ℃ (standard requirement). ④ If the calibration result exceeds the standard limit, the equipment needs to be shut down for troubleshooting (such as aging heating tubes, sensor displacement, poor sealing, etc.), repaired, and recalibrated.

4、 Calibration precautions

1. Key points of safety protection

① When calibrating low temperature points (such as -40 ℃, -70 ℃), operators should wear anti freezing gloves and goggles to avoid frostbite caused by contact with low-temperature components inside the box; When calibrating high temperature points (such as 150 ℃, 200 ℃), it is necessary to wear heat-resistant gloves to prevent burns. ② During the operation of the equipment, it is forbidden to open the box door. If the sensor position needs to be adjusted, the equipment should be paused first and the temperature should be restored to room temperature before operation. ③ If the test chamber uses liquid nitrogen and refrigerant assisted refrigeration, it is necessary to check the sealing of the pipeline to prevent refrigerant leakage from causing safety hazards.

2. Avoid interfering factors

① During the calibration process, the test chamber should be empty and no test samples or unrelated items should be placed to avoid the influence of sample heat absorption/release on the temperature field inside the chamber. ② The wires of the data acquisition instrument need to be organized and standardized to avoid entanglement or contact with high/low temperature areas on the box wall, in order to prevent wire damage or affect measurement accuracy. ③ Avoid collecting data during the heating and cooling stages of the device, only during the constant temperature stage after the temperature has stabilized, to ensure the authenticity of the data.

3. Maintenance of equipment and appliances

① Before and after calibration, it is necessary to clean the inside of the test chamber, remove dust and stains from the chamber walls, check the door seals, and replace them in a timely manner if there is aging to ensure sealing performance. ② Temperature sensors and data acquisition devices need to be regularly calibrated, avoiding collisions and moisture during the calibration process, and properly stored after use. ③ After calibration is completed, restore the temperature of the test chamber to room temperature, turn off the power, clean the site, and keep records of equipment usage and calibration.

4. Calibration cycle requirements

The calibration cycle for high and low temperature test chambers is usually 1 year; If the equipment is used frequently, in harsh environments (such as high temperature, high humidity, and high dust), or for critical product testing, it is recommended to shorten the calibration cycle to 6 months. Calibration must be completed by qualified metrology institutions or professionals to ensure that the calibration results have legal validity and credibility.

V. Summary

　　High and low temperature test chamberCalibration is a key step in ensuring the reliability of experimental data, and it is necessary to strictly follow national standards to standardize the processes of point placement, constant temperature, data acquisition and processing. At the same time, attention should be paid to the preparation work before calibration and safety protection in practical operation, avoiding various interference factors, in order to ensure the accuracy of calibration results. Regular calibration can not only timely detect equipment hazards and extend equipment service life, but also provide strong technical support for product quality testing and scientific research experiments.