This term is used for the repeated sampling of a component. Decay measurements are performed to check whether the number of particles removed diminishes, thus showing that a suitable extraction process has been chosen.
The decay measurement helps to establish the suitable sampling conditions and to set up a “test specification" for the respective component.
A sufficient number of identical components need to be provided to perform the measurements.
Decay measurement sequence:

• Define suitable sampling conditions and the number of test objects.
• Determine the blank value of the analysis system without component.
• Perform repeated sampling operations on the components with the chosen parameters.
• For each sampling, strictly adhere to the selected parameters, the defined amount of fluid and/or the test period.
• Precisely determine the cleanliness value of the analysis fluid.
• Divide the cleanliness value of the last sampling performed by the sum of all the cleanliness values already measured.
• Decay criterion: sampling is considered complete if the ratio is ≤ 10% compared to the total amount.
• If the ratio is > 10%, another sampling needs to be performed.