The accuracy of the test results of a linear constant temperature and humidity testing machine (simulating a specific temperature and humidity environment to test the weather resistance and stability of materials/products) depends on the "accuracy of environmental parameter control" and "stability of sample state", and its deviation is influenced by 12 key factors in four dimensions: equipment performance, sample characteristics, operating methods, and environmental conditions. The following analysis is conducted from mechanism to instance to clarify the specific interference of each factor on the test results:
1、 Equipment Performance: The Hardware Basis for Temperature and Humidity Control Accuracy
The core components of the equipment (refrigeration, heating, humidification, temperature control system) directly determine the consistency between the "set environment" and the "actual environment", which is the fundamental factor affecting the results:
1. Stability of temperature and humidity control system
Efficiency degradation of heating/cooling module
After long-term use of heating tubes (such as stainless steel heating tubes), surface scaling (such as scale adhesion caused by humidification), or refrigerant leakage in refrigeration systems (such as compressors and evaporators), can lead to "insufficient heating/cooling rate" - for example, setting "from 25 ℃ to 80 ℃ (rate 5 ℃/min)", which can only reach 3 ℃/min in reality, resulting in a shortened exposure time of the sample at the target temperature, and test results tend to be "good weather resistance" (such as material aging degree lower than the actual level).
Insufficient accuracy of humidification/dehumidification module
Scaling of humidification tanks (affecting steam production) and blockage of dehumidifiers (such as capillaries) can lead to humidity control deviations: for example, setting "60% RH" but actual humidity fluctuates between 50% -70% RH (exceeding the standard allowable ± 3% RH range). Samples that are sensitive to humidity, such as electronic components and paper, may experience measurement deviations in the "moisture failure time" due to unstable actual humidity (such as failure after 24 hours due to low humidity, but only after 36 hours due to low humidity).
2. Uniformity of airflow circulation in the studio
The accumulation of dust on the fan blades and blockage of the air ducts inside the studio can lead to uneven airflow distribution, forming a "local temperature and humidity blind spot": for example, the temperature in the corner of the studio is 5 ℃ lower than the center, and the humidity is 10% lower RH. If the samples are placed in the blind spot area, there will be "significant differences in the test results of the same batch of samples" (such as some samples passing and some failing), which violates the basic principle of "testing in the same environment".
3. Sensor accuracy and calibration status
Temperature and humidity sensors (such as platinum resistors Pt100 and humidity capacitors) are the "sensing organs" of equipment. If they are not calibrated for a long time (the standard requires calibration every 6-12 months), there will be "measurement drift": for example, if the actual temperature is 30 ℃ and the sensor displays 28 ℃, the equipment will continue to heat up to the set 30 ℃, causing the actual temperature in the workshop to reach 32 ℃, and the sample will accelerate aging due to "overheating" (such as premature brittleness of plastic parts).
Improper installation of sensors (such as near the heating tube or away from the airflow area) can lead to "local perception" replacing "overall environment", which can also cause control deviations.
2、 Sample characteristics and placement method: "state interference" of the test object
The physical/chemical properties of the sample itself and the "environmental interaction mode" during placement can lead to differences in the actual temperature and humidity it can withstand compared to the studio environment
1. Thermal capacity and moisture absorption of the sample
The heating/cooling rate of samples with large heat capacity (such as metal blocks and thick plastic parts) is slower than that of the working environment: for example, the working environment has risen to 80 ℃, but the core temperature of the sample is still 60 ℃, resulting in the "actual high temperature time experienced by the sample" being shorter than the set time, and the test results are biased towards "good temperature resistance" (such as the strength decrease of metal parts being lower than the actual level).
Highly hygroscopic samples (such as wood and textiles) can absorb moisture in the workspace, leading to a decrease in local humidity. For example, when testing a sponge in a 60% RH environment, the surrounding humidity drops to 45% RH after the sponge absorbs water. The sample's own "moisture deformation" is smaller than the results in a real high humidity environment, and it is mistakenly judged as "moisture resistance qualified".
2. Size, quantity, and placement of samples
Sample size too large/stacked placement: If the sample volume exceeds 1/3 of the working chamber volume (standard requirement ≤ 1/3), or if multiple samples are stacked (such as paper placed in multiple layers), it will hinder airflow circulation, causing the surface temperature and humidity of the sample to be unable to synchronize with the working chamber - for example, the internal temperature of the stacked cardboard box is 8 ℃ lower than the surface, and the humidity is 15% RH higher, resulting in a contradictory result of "surface not moldy, internal moldy".
Contact between the sample and the studio wall: The sample is directly attached to the metal wall of the studio (the wall temperature is easily affected by the external environment, such as the wall temperature being higher than the interior of the studio in summer), which can cause local temperature anomalies in the sample. For example, electronic components attached to the wall may fail prematurely due to high wall temperature, leading to misjudgment as "poor temperature resistance".
3. Sample preprocessing status
Before testing, if the sample is not pre treated according to the standard (such as equilibrating for 24 hours in an environment of 23 ℃ and 50% RH), the "initial temperature and humidity" carried by the sample itself will interfere with the test. For example, if a sample taken from a low-temperature warehouse (initial temperature of 10 ℃) is directly placed in a testing machine at 30 ℃, the sample will first absorb heat and rise in temperature, during which "condensation water" may occur (due to surface humidity saturation caused by sudden temperature rise), resulting in failure caused by non environmental factors such as "sample corrosion", which is mistakenly judged as "corrosion failure in high humidity environment".