How do the temperature uniformity and fluctuation of the high and low temperature test chamber affect the test results?

Temperature uniformity and temperature fluctuation are the core accuracy indicators of high and low temperature test chambers, which directly determine the "authenticity" and "stability" of the testing environment - the essence of the test results is the "performance response of the product at the target temperature". If these two parameters do not meet the standards, it is equivalent to "the product was not tested at the set temperature", ultimately leading to data distortion, product evaluation deviation, and even serious quality misjudgment.

Below, based on actual testing scenarios, we will analyze the specific impact of both on the test results:

1、 First, clarify the core definition

Temperature uniformity: The maximum temperature difference between each test point in a stable state within the effective space of the test chamber. For example, setting -40 ℃, some points inside the box -38 ℃, some points -42 ℃, the uniformity is 4 ℃.

Temperature fluctuation: The short-term fluctuation amplitude of the temperature at a certain test point around the set value when the test chamber is in a constant temperature state. For example, if the temperature is set to 85 ℃ and fluctuates repeatedly between 84.3 ℃ and 85.7 ℃, the fluctuation is 1.4 ℃.

2、 Temperature uniformity: affecting the consistency of the testing environment in various parts of the sample

Core issue: Different parts of the sample are at different temperatures, which is equivalent to undergoing multiple temperature tests simultaneously, and cannot reflect the true performance of the product.

1. Impact on electronic/electrical products

Scenario: Testing mobile phone circuit boards, chips, battery packs, etc., with large sample volumes or complex structures.

influence:

If the uniformity is poor, the core area of the chip may be at 85 ℃, but the edge interface area may reach 89 ℃, causing the interface to fail at high temperatures first, while the chip itself has not reached the failure threshold - misjudging as "product high temperature stability unqualified";

On the contrary, if some of the battery cells in the battery pack are at -40 ℃ and some are at -36 ℃, the capacity decay of the cells at -40 ℃ is more severe at low temperatures, while the cells at -36 ℃ perform normally, it may be mistaken as "the low-temperature performance of the battery pack meets the standard", but in actual use, there may be problems such as insufficient capacity and inability to start.

Consequence: Electronic products frequently malfunction in * * environment after leaving the factory, or qualified products are misjudged as unqualified.

2. Impact on materials/components

Scenario: Testing the weather resistance of plastic shells, rubber seals, and automotive interior parts.

influence:

Plastic parts located in high temperature zones can accelerate the thermal aging, yellowing, and brittleness of that area, while other areas have insufficient aging, resulting in "local failure" of the tested product, which cannot reflect the overall weather resistance - in actual use, the product may be damaged first in non tested high temperature zones;

During low-temperature testing, some areas of the rubber seal were at -40 ℃ and some were at -35 ℃. After testing, it was observed that "some areas cracked", making it impossible to determine whether it was a quality problem with the product itself or a local stress concentration caused by uneven temperature. The test data lost its reference value.

Consequence: Material selection errors, early aging and sealing failure of the product in actual use.

3、 Temperature fluctuation: affecting the stability of temperature stress borne by the sample

Core issue: Frequent temperature fluctuations are equivalent to adding "periodic thermal shock" to the sample, rather than a stable constant temperature environment, resulting in test results deviating from the actual operating conditions.

1. Impact on stability testing of electronic components

Scenario: Test the long-term constant temperature stability of chips and sensors, and evaluate their parameter drift.

influence:

Setting the temperature to 85 ℃, if the fluctuation reaches ± 1 ℃ and the temperature fluctuates frequently between 84~86 ℃, the parameters of electronic components will drift with temperature changes, making it difficult to distinguish whether "parameter drift is caused by the aging of the product itself or temporary changes caused by temperature fluctuations";

Sensitive components may experience "thermal expansion and contraction fatigue" due to frequent temperature changes, accelerating internal solder joint oxidation and lead breakage, resulting in a shorter testing life.

Consequences: Misjudging component stability, qualified products being eliminated, or unqualified products entering the market.

2. Impact on material thermal aging/brittleness testing

Scenario: Testing the high-temperature aging life of plastics and rubber, or low-temperature brittleness testing of metal materials.

influence:

During high-temperature aging, temperature fluctuations can cause materials to undergo repeated thermal expansion and contraction, which is faster than the aging rate under stable high temperatures. For example, plastics that were originally stable for 1000 hours at 120 ℃ may age and crack after 500 hours in an environment with fluctuations of ± 1 ℃, resulting in a shorter lifespan assessment;

During low-temperature embrittlement testing, temperature fluctuations can cause the material to switch between a "embrittlement state" and a "near embrittlement state", making it difficult to accurately determine the critical embrittlement temperature of the material, and the test data loses its reference value.

Consequences: Distortion in material life assessment, insufficient redundancy in product design life, and premature failure in actual use.

3. Impact on batteries and chemical products

Scenario: Testing the high and low temperature charging and discharging performance of lithium batteries.

influence:

Temperature fluctuations can lead to unstable internal chemical reaction rates in batteries: sudden temperature increases during discharge, accelerated reactions, and higher capacity test values; The temperature suddenly drops, the reaction slows down, and the capacity value is low, making it impossible to obtain real capacity data;

The stability testing of chemical materials may cause side reactions due to temperature fluctuations, leading to deviations between test results and actual working conditions, and even misjudging material safety.

Consequences: The actual capacity of the battery product does not meet the standard after leaving the factory, or there are safety risks during the use of chemical products.

4、 The combined impact of the two: test results being 'invalid' or 'misleading decisions'

Not meeting testing standards: Most industry standards have clear requirements for uniformity and fluctuation. If the parameters do not meet the standards, the test data will not be recognized and the product will not pass certification;

Misjudgment of product quality:

False qualification ": Due to uniformity/fluctuation issues, the product did not experience a real * * environment during testing and was mistakenly judged as qualified. After leaving the factory, it frequently malfunctions during actual use;

Fake unqualified ": Due to environmental temperature deviation, qualified products are judged as unqualified, which increases the cost of rework and scrapping for enterprises and reduces production efficiency;

Misleading research and development direction: If the research and development stage relies on distorted test data, it may mistakenly believe that the product has certain defects, and then invest a lot of resources to optimize non-existent problems, or ignore the real weak points.

Proper use of equipment:

The sample volume shall not exceed one-third of the inner container volume and shall not obstruct the air duct;

Before conducting a constant temperature test, allow the device to "preheat/pre cool" for 30 minutes, and then place the sample after the temperature stabilizes;

Pay attention to technical details when selecting: prioritize models with "forced air circulation system" and "high-precision PID temperature control" to avoid low-priced and inferior equipment.

summary

Temperature uniformity determines whether various parts of the sample are at the same target temperature, while fluctuation determines whether the sample is at a stable target temperature - both directly affect the authenticity of the testing environment. Only when these two parameters meet the standards can we ensure that the test results reflect the performance of the product in a real environment, avoiding quality risks, cost waste, or misleading research and development caused by data distortion.