Blank value testing, in the early stages, many customers and even testing institutions may not necessarily perform this step when conducting cleanliness testing. With the promotion of the VDA19/ISO16232 cleanliness standard and the continuous popularization of cleanliness knowledge, most customers must understand the importance of blank values. The blank value is used to confirm whether the cleanliness extraction equipment meets the testing indicators.
The principle of blank values
The cleanliness inspection of parts involves the risk of introducing external impurities into the analysis results. If the proportion of foreign particles (blank) is too high, it may lead to a certain amount of misjudgment. The blank value represents the impurities not originating from the sample. These foreign particles may originate from:
-Cleaning and rinsing solutions
-Cleaning equipment (containers, tanks, pipelines, exhaust facilities, etc.)
-Operation during analysis and cleaning process
-Environment and personnel
-All objects in contact with the sample and cleaning solution
The cleanliness of the testing environment must meet the required cleanliness status of the sample.
Derive blank values
1. Weight limit: ≤ 10% (detection value)
2. Particle size limit: ≤ 10%, rounded to the nearest whole number
3. Maximum particle: half of the maximum particle and at the lower limit of the interval
4. If the blank level exceeds 10%, the number of test components analyzed can be increased, allowing for the collection of more particles to meet the 10% limit.
Blank value criterion and examples
Exceptions may occur in
----Active modules, such as valves, pumps, injectors, etc
----Parts that release particles themselves, coatings
----Highly clean components (with very small weight limits and a small total particle count)