Secondary Gas Standards from NPL are certified directly against a selection of NPL PSMs using in-house validated analytical instrumentation which has demonstrated repeatability and linearity. In practice, at least two sets of NPL PSMs are used on different days for this certification. The value obtained from this certification is compared with the gravimetric value obtained for the concentration of the Secondary Gas Standard during its preparation - in order to check for consistency. The value on the NPL certificate, is that obtained from the analytical certification process with the appropriate measurement uncertainty.

See also:

• What is the NPL Gas Standards Hierarchy? (FAQ - Gas Standards)
• What is a Primary Standard Gas Mixture (PSM)? (FAQ - Gas Standards)
• What is a Primary Reference Gas Mixture (PRGM)? (FAQ - Gas Standards)
• What is a Certified Reference Gas Mixture (CRGM)? (FAQ - Gas Standards)