When performing high-temperature tests in the high and low temperature test chambers, the temperature inside the chamber is stable, but the samples placed at the corners deviate greatly from the actual set temperature. What should be done?

1. Analysis of the Cause of the Problem

The "control panel display is stable but actual temperature field is uneven" described as a typical and common issue, not because of the temperature control algorithm itself, but because of the following core aspects:

• Air circulation system obstruction: The test chamber relies on fans to drive air circulation inside the chamber to create a uniform temperature field. If the duct design is limited or the fan power is insufficient, airflow dead corners are easily created. Poor airflow is one of the common causes of excessively poor temperature uniformity.

• Improper sample placement: If the product to be tested is too large, placed too densely, or severely blocks the internal airflow channels, it can cause local temperature abnormalities around the sample. When test items are stacked to block the air outlet area by more than 30%, it will disrupt the airflow path.

• Dust accumulation on the return air outlet filter: If the filter at the return air outlet on the back of the cabinet is heavily dusted, it will greatly reduce airflow efficiency. Poor return air directly affects temperature uniformity indicators.

• Poor sealing of the cabinet door: Aging or deformation of the door seal can allow cold air from outside to seep in, especially under high-temperature conditions, where the infiltrating cold air can cause local cooling.

2. Detailed Inspection and Operational Methods

Step 1: Check the operating status of the air circulation system

When the machine is powered on and running, open the door and feel by hand whether there is noticeable airflow at the air outlet inside the box. Under normal conditions, you should feel a regular airflow circulation. Check the air circulation duct on the back of the cabinet for obvious blockages (such as fallen label paper, tools, etc.). Find the filter at the return air outlet and remove it to observe—if the filter is covered with dust (especially cotton-like dust), it means the air path is severely obstructed. Cleaning method: Soak the filter screen in a neutral detergent for 10 minutes, scrub with a soft brush, rinse with clean water, dry completely, then reassemble.

Additionally, monitor the fan's operating sound—if there are abnormal noises or significantly low speeds, it indicates wear on the motor bearings or aging of the starting capacitors. A clamp meter can be used to measure the operating current of the fan and compare it with the nominal value on the equipment nameplate. If the current is significantly low, it indicates insufficient fan output and requires contact with the manufacturer for repair or replacement.

Step 2: Check the door sealing strip

Cut A4 paper into strips 5cm wide, and with the box door closed, clamp the strip between the door seal and the box body, then try to pull it out. If the paper strip can be pulled out with almost no resistance, it indicates that the door seal has aged, deformed, and is not tightly sealed. Open the box door and carefully inspect the seal for cracks, hardening, or permanent dents. If the sealing is confirmed, contact the manufacturer to replace the original factory door seal.

Step 3: Standardize sample placement

According to standard requirements, ensure there is sufficient space between the items under test and between the items and the box wall (usually more than 10 cm is recommended) to ensure unobstructed airflow. Pay special attention: samples should not be directly blocked by the air outlet, nor should they be stacked too high to block the return air outlet. Samples should preferably use hollow sample racks or trays to reduce airflow obstruction.

Step 4: No-load testing to diagnose the source of the problem

Operating method: Remove all samples from the test chamber, keep the load idle, and arrange 9 temperature measurement points inside the chamber (3 on the upper layer, 3 in the middle layer, and 3 on the lower layer, covering the entire workspace). After running high-temperature tests (such as 85°C) and stabilizing for 2 hours, measure the temperature at each point using a multi-channel temperature recorder that has been calibrated for metrological measurement. If the temperature uniformity under no-load conditions meets the standard (within ±2.0°C), it indicates that the chamber's performance is qualified; the problem lies in sample placement or excessive loading. If uniformity still exceeds the standard under no-load conditions, it indicates defects in the equipment itself (such as fan faults, duct structure issues, etc.), and professional engineers from the manufacturer should intervene and repair the issue.

Step 5: Daily prevention and regular maintenance

• It is recommended to check the fan's operating status every 3 months and clean the return air filter screen; Check the seal seal every six months.

• After the high-temperature test, it is recommended to open the door for a period of time to let the temperature inside drop to room temperature before closing it, thereby extending the seal's lifespan.

• Each time a sample is placed, it is recommended to photograph and record the sample layout and establish a "sample layout archive" to facilitate reproducing the same temperature field conditions across different batches of testing.