IEC 60068 2 5 Edition 2 0 2010 04 INTERNATIONAL STANDARD NORME INTERNATIONALE Environmental testing – Part 2 5 Tests – Test Sa Simulated solar radiation at ground level and guidance for solar radiatio[.]
General
Throughout the test, it is essential to maintain the irradiation, chamber temperature, humidity, and other specified environmental conditions at levels suitable for the designated test procedure outlined in the relevant specification, which will also detail the necessary preconditioning requirements.
Temperature
The temperature within the chamber during irradiation and darkness periods shall be controlled in accordance with the procedure (A, B or C) specified During irradiation, the temperature
MECON Limited, located in Ranchi and Bangalore, is licensed for internal use of materials supplied by the Book Supply Bureau The temperature within the chamber must change at a rate of 1 K/min and be maintained at one of the specified values outlined in IEC 60068-2-1, IEC 60068-2-2, or the applicable standards.
NOTE Additionally, a black standard thermometer can be used to control the maximum surface temperature By ventilation, this temperature can be influenced.
Humidity
Different humidity conditions, particularly condensation, can markedly affect photochemical degradation of materials, paints, plastics, etc If required, the values of IEC 60068-2-78 shall be preferred
The relevant specification shall state the humidity and whether it is to be maintained during a) the irradiation periods only; b) the periods of darkness only; c) the whole test duration.
Ozone and other contaminating gases
Ozone, generated by short wavelength ultra-violet of test sources, will normally be excluded from the test chamber by the radiation filter(s) used to correct the spectral energy distribution
To ensure accurate testing, it is crucial to eliminate ozone and other contaminating gases from the test chamber, unless specified otherwise by relevant standards, as these gases can greatly influence the degradation processes of specific materials.
Surface contamination
Dust and surface contamination can greatly alter the absorption properties of irradiated surfaces It is essential to test specimens in a clean state unless specified otherwise If the impact of surface contamination needs to be evaluated, the relevant specifications must provide detailed information on surface preparation and related procedures.
Mounting of specimen
The specimen for testing must be positioned on a raised support, turntable, or a designated substrate with known thermal conductivity and capacity, ensuring adequate spacing from other specimens to prevent shielding from radiation or re-radiated heat Additionally, temperature sensors should be affixed to the specimen as necessary.
Test facility
It shall be ensured that the optical parts of the test facility, lamps, reflectors and filters, etc are clean
The level of irradiation over the specified measurement plane shall be measured immediately prior to each test
Any ancillary environmental conditions, e.g ambient temperature, humidity and other parameters if specified, should be monitored continuously throughout the test.
Test apparatus
The testing chamber must be equipped to achieve an irradiance of 1,120 W/m² ± 10% over the specified measurement plane, as detailed in Table 1 This irradiance value of 1,120 W/m² should account for any radiation reflected from the chamber that reaches the specimen, but it must exclude long-wave infrared radiation emitted by the chamber itself.
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Means shall also be provided whereby the specified conditions of temperature, air flow and humidity can be maintained within the chamber
The chamber's temperature must be measured at a horizontal plane between 0 mm and 50 mm below the designated irradiation measurement plane This measurement should be taken at the midpoint between the test specimen and the chamber wall, or at a distance of 1 m from the specimen, depending on which distance is shorter.
The specimen shall be submitted to the visual, dimensional and functional checks prescribed by the relevant specification
General
The chamber's temperature must change at a rate of 1 K/min during exposure and be held at one of the specified values outlined in IEC 60068-2-1, IEC 60068-2-2, or the applicable specification.
In procedure A, the temperature within the chamber shall start to rise 2 h before the irradiation period starts
During the dark phase of procedures A and B, the chamber temperature will decrease at a rate of approximately 1 K/min and will be held at +25 °C If a temperature lower than 25 °C is necessary, it will be maintained at that specified lower temperature.
The requirements for irradiation, temperature and time relationships are given in Figure 2
Throughout the specified test duration, the temperature within the chamber shall be maintained within ±2 °C of that shown for the appropriate procedure
The level of irradiance should be 1 120 W/m 2 ± 10 % or specified in the relevant specification
Increasing the irradiation beyond the recommended level to accelerate testing is not advisable Procedure A simulates total daily irradiation that reflects the most extreme natural conditions, with an exposure duration of 8 hours per day under standard irradiation conditions.
Thus, exposure for periods in excess of 8 h will effect acceleration over natural conditions
However, continuous exposure of 24 h per day, procedure C, might mask any degradation effects of cyclic thermal stressing, and this procedure is therefore not generally recommended in this instance
The specimen shall be exposed, for the duration called for in the relevant specification, to one of the following test procedures (see Figure 2).
Procedure A – 24 h cycle, 8 h irradiation and 16 h darkness, repeated as required
This gives a total irradiation of 8,96 kWh/m 2 per diurnal cycle, which approximates to the most severe natural conditions Procedure A should be specified where the principal interest is in thermal effects.
Procedure B – 24 h cycle, 20 h irradiation and 4 h darkness, repeated as required
This gives a total irradiation of 22,4 kWh/m 2 per diurnal cycle and is applicable where the principal interest is in degradation effects
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Procedure C – Continuous irradiation as required
This simplified test is designed for scenarios where cyclic thermal stressing is not a significant factor and focuses solely on evaluating photochemical effects It is also suitable for assessing the heating effects on specimens that possess low thermal capacity.
Time (h) Continuous irradiation (for required duration)
T 1 lower temperature (25 °C if not otherwise specified)
T 2 upper temperature (40 °C if not otherwise specified)
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The specimen shall be submitted to the visual, dimensional and functional checks prescribed by the relevant specification
9 Information to be given in the relevant specification
The relevant specification must include details such as exposure time to radiation, black standard temperature, power of radiation, duration of the test, state of operation, preconditioning, number of specimens, humidity if applicable, type and scope of initial measurement, test procedure, temperature during the test, period of operation, type and scope of intermediate measurement, recovery, type and scope of final measurement, criteria for evaluation, type and scope of test report, and a description of the specimen support used for testing.
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10 Information to be given in the test report
When including this test in the relevant specification, it is essential to provide details such as the test laboratory's name, address, and accreditation, along with the test dates and customer information The type of test conducted (A, B, or C) and the required values like temperature, humidity, and radiation should be specified, along with the test's purpose, whether for development or qualification Additionally, the applicable test standard (e.g., IEC 60068-2-5) and the relevant laboratory test procedure must be noted A description of the test specimen, including drawings or photos, and details about the test chamber, such as the manufacturer and model number, are also necessary The performance of the test apparatus, measurement uncertainties, and calibration data should be documented, along with initial, intermediate, and final measurements Required and actual test severities, results of functional tests, and any observations made during testing, including actions taken, should be summarized Finally, a distribution list for the test summary should be included.
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The relevant specification must outline the allowable alterations in the external conditions and performance of the test specimens following exposure to the designated level of irradiation for specified durations Additionally, various aspects of interpretation should be taken into account.
Primarily, heating effects are concerned Short-term effects to be looked for will mainly be in the nature of local overheating
Long-term tests aim to identify deterioration patterns by evaluating initial rapid changes and assessing the item's useful life.
The maximum surface and internal temperatures of a specimen or equipment are influenced by several factors, including the ambient air temperature, radiation intensity, air velocity, exposure duration, and the object's thermal properties such as surface reflectance, size, shape, thermal conductance, and specific heat.
Equipment can reach temperatures over 80 °C when fully exposed to solar radiation, even in ambient temperatures as low as 35 °C to 40 °C The surface reflectance significantly influences temperature increases due to solar heating; for instance, switching from a dark color to a glossy white finish can lead to a substantial temperature reduction However, a pristine finish intended to lower temperatures may deteriorate over time, ultimately causing an increase in temperature.
Most materials exhibit selective reflectance, meaning their spectral reflectance factor varies with wavelength For example, while paints are generally poor reflectors of infrared light, they can be highly efficient in the visible spectrum Additionally, many materials experience a sharp change in their spectral reflectance factor between the visible and near-infrared regions, which affects color perception Therefore, it is crucial for the spectral energy distribution of radiation sources used in simulated tests to closely mimic natural solar radiation, or to adjust the irradiance accordingly to achieve equivalent heating effects.
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Weathering refers to the combined effects of solar radiation, atmospheric gases, temperature, and humidity changes, leading to the aging and eventual degradation of organic materials such as plastics, rubbers, paints, and timber.
Materials that perform well in temperate climates often fail to meet the demands of tropical conditions Common issues include the swift deterioration of paints, the cracking and breakdown of cable sheathing, and the fading of pigments.
The weathering of materials typically involves multiple simultaneous reactions rather than a single process, with various factors interacting While solar radiation, particularly ultraviolet (UV) light, is a significant contributor to photo-degradation, its effects are often intertwined with other weathering influences For instance, in polyvinyl chloride, the impact of UV radiation alone appears minimal; however, its vulnerability to thermal breakdown, likely exacerbated by oxygen, is significantly heightened.
Artificial tests can lead to abnormal defects not seen in natural weathering due to several factors: a) laboratory sources of ultra-violet radiation often differ significantly from natural solar radiation in their spectral energy distribution; b) increasing the intensity of ultra-violet radiation, temperature, and humidity to accelerate effects does not uniformly enhance the rates of individual reactions compared to normal exposure; c) these tests typically fail to replicate all the factors involved in natural weathering.
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The radiation source may comprise one or more lamps and their associated optical components, e.g reflectors, filters, etc., to provide the required spectral distribution and irradiance
Depending on place, time, irradiance, spectral distribution and power of radiation, different lamps with different filters can be used
The selection of filters is influenced by the source, equipment, and spectral distribution, with a current preference for glass filters However, glass filters may not provide the same level of reproducibility as chemical solutions Adjustments may be required to account for varying optical densities through different plate thicknesses Since glass filters are proprietary, it is advisable to consult manufacturers for recommendations on suitable filters for specific applications, as the choice will depend on the source and its intended use.
Excessive exposure to ultra-violet radiation can cause rapid changes in the spectral characteristics of some glass infra-red filters To mitigate this deterioration, it is advisable to place an ultra-violet filter between the radiation source and the infra-red filter Interference type filters, which reflect unwanted radiation rather than absorb it, tend to be more stable than absorption filters, as they reduce the heating of the glass.
Due to the sun's distance from the earth, solar radiation reaches the surface as nearly parallel beams In contrast, artificial light sources are closer to the working surface, necessitating methods to direct and focus the light to achieve uniform irradiance at the measurement plane, ideally within the specification limits of 1,120 W/m² ± 10% A long-arc lamp paired with a parabolic trough reflector facilitates more consistent irradiation Additionally, advanced mounting techniques and the use of a turntable can help achieve uniformity across larger surfaces with multiple lamps.