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Monitoring of Test Tolerances

Monitoring The Conditions of Exposure

A typical weathering test includes four test parameters: 

  • Irradiance
  • Chamber air temperature
  • Relative humidity
  • Black panel temperature
  • Water spray may be added as fifth parameter when applying cyclic wetting of the test specimens.

    Best practice for any weathering instrument is not only to record all relevant test parameters as time-dependent values. They also need to be monitored against their allowed min/max tolerances which are often specified in testing standards. These min/max tolerances are also called “allowed operational fluctuations".

    Consequences of Missing Parameter Check Feature

    What are the consequences if a weathering device does not have this feature? Does it make a difference?

    Imagine you are testing to a particular standard which specifies a min and max tolerance for irradiance,
    e.g. (60 ± 2) W/m². If there is an issue with the weathering device and the irradiance has been running at 67 W/
    m² without you being aware of this. Then, the test has been running for 1000 h and samples have been exposed by 5 W/m² above maximum for this duration. The samples failed by showing significant degradation. There were no error message and the instrument did not stop. As a result, you have not tested according to the standard - you have lost 1000 hours, and your samples failed.
    Now imagine the reverse: 5 W/m² less than the minimum tolerance for a duration of 1000 h. Samples passed, no error messages and the instrument did not stop. Now you have underexposed your samples, and therefore did not test according to the standard. As a result, you may potentially release a bad product which would not have passed the standard and may fail in the field.

    As you see, the consequences for both cases may be severe.

    Does Your Weathering Device Have a Parameter Check Feature?

    To avoid any test parameter exceeding its allowed tolerances, Atlas Ci, Xenotest, and SUNTEST weathering instruments allow for programming those tolerances. This is a safety for standard compliant test conditions throughout the complete test duration. The “switch off time” setting should be aligned to the time required for the instrument to reach equilibrium, mostly the time needed after a “cold” start of a test.

    SUNTEST XXL+ programming step “Parameter monitoring” using typical example: E: ± 2 W/; CHT: ± 3 K; BST: ± 3 K; RH: ±10 %; “Switch off time” 30 min; max BST: 70°C

    We suggest that next time you consider a new weathering chamber or any other test device you should have a closer look on the “Parameter Check” feature. Think about potential consequences for your test results if this feature is missing.

    More Information

    For further information on instruments and weathering testing have a look into our online library, listen to recorded online seminars or review upcoming educational classes.

    Check out Atlas latest online DAQ software WXView II.