The Truth About Aluminium Oxide

Still using Aluminium Oxide probes? The performance capabilities don't always match manufacturers' claims.

 

The United States' National Institute of Standards & Technology (NIST) is one of the world's foremost bodies in the field of scientific measurement and international standards. Until 1988 the organisation operated under the name National Bureau of Standards (NBS), and it was during this time that significant research was conducted in to the performance of Aluminium Oxide moisture sensors.

Led by Saburo Hasegawa, at the time Chairman of NBS, the in-depth tests revealed significant shortcomings in the technology's ability to provide meaningful data capture. In particular, it was documented that Aluminium Oxide sensors have the following significant deficiencies:

 

  • Lack of Sensitivity  -  the sensitivity of individual sensors decays over time, and the relative sensitivities of two individual sensors can vary by a factor of two.
  • Calibration Drift  -  sensors have a natural tendency to drift to the dry end of the scale (even under clean-gas conditions - i.e. storage in N2) - drift was recorded at as much as 76% within two months of calibration.
  • Slow Speed of Response  -  the sensors are prone to slow response, especially following exposure to high moisture concentrations in the sample gas.
  • Temperature Interference  -  displayed moisture readings are affected by variations between calibration temperature and operational (sample gas) temperature.

 

In some instances it was discovered that individual sensors would display all characteristics at once (i.e.: slow speed, continual downward drift and calibration shift), almost as soon as testing had commenced. Such levels of performance should force all users of such sensors to ask serious questions of their supplier - not least when challenging some of the unrealistic claims that manufacturers often make.

It should be noted that this study was made in 1980. Almost 30 years later many users are still suffering the same issues of slow response speed, lack of sensitivity, calibration drift and the effect of temperature. The presentation from the manufacturers may change, but the technological flaws remain.

For the full story, download the detailed report below.

To learn about critical factors in moisture measurement, including Manalytical's unique sensor technology, click here.

 

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