SEMI C15 - Test Method for ppm and ppb Humidity Standards -

This Standard was technically approved by the Gases Global Technical Committee. This edition was approved for publication by the global Audits and Reviews Subcommittee on March 16, 2016. Available at www.semiviews.org and www.semi.org in June 2016; originally published in 1995; previously published February 2012.

This Test Method will determine whether or not the quantity of moisture delivered by a gaseous moisture standard is in agreement with that predicted for the standard on the basis of physical principles. It is expected that this Test Method will be used to validate moisture standards before they are first placed in use, when deviation from expected performance is likely or suspected, and at other times as seems necessary.

This Test Method assumes the existence of a reliable moisture analyzer. Although extensive precautions are described to ensure the validity of the analyzer, it is always possible that the test could yield a faulty result through some unforeseen defect in the analytical equipment.

Given that moisture generation is subject to many pitfalls, it will be required that the predicted moisture concentration delivered by the standard and the measurement of that level by the analyzer agree. The level of agreement can vary depending on the degree of precision claimed for the moisture standard, but in any case the measured and predicted results should be within 10% over the entire range of the moisture standard. If not, then the validation should be repeated after verifying the physical measurement upon which the prediction is based and any other parameters deemed suspect.

This Test Method is intended to be applicable to any type of gaseous standard delivering a quantity of moisture in the ppm range or lower, provided the delivered moisture concentration is predictable on the basis of fundamental principles of physics. Thus, any standards which rely solely on characterization by analysis are specifically excluded.

As part of this Test Method, a procedure is described for qualifying certain moisture analyzers considered suitable for use in qualifying moisture standards. Moisture analyzers intended for other applications may need to satisfy different criteria.

As the most accurate and reliable moisture analyzers currently available operate primarily in the ppm range, this Test Method focuses on validation of moisture standards in this range. The need for ppb moisture standards is addressed by specifying procedures for reducing the output of ppm moisture standards to the ppb range.

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