1、 Reduce the impact of other geometric shape errors

The purpose of specifying the sampling length (i.e. a part or basis of the evaluation length) is to limit and reduce other geometric errors, especially the influence of surface wave roughness on the measurement results. Surface roughness and surface wave roughness are two different surface geometric features, but in actual measurements, they may coexist and affect each other. By specifying the minimum evaluation length, it can be ensured that this influence can be fully considered during the measurement process, thereby obtaining more accurate measurement results.

2、 Ensure the representativeness of measurement results

The surface roughness of components is usually uneven, which is caused by various factors during the machining process. If the evaluation length is too short, it may not fully reflect the overall roughness characteristics of the surface, resulting in a lack of representativeness in the measurement results. By specifying the minimum evaluation length, it can ensure that more surface areas can be covered during the measurement process, thereby obtaining more representative measurement results.

3、 Compliant with international standards and regulations

In international standards and specifications, there are usually clear provisions for measuring roughness and evaluating length. These standards and specifications aim to ensure the accuracy and comparability of measurement results. By adhering to the minimum evaluation length requirement, it is possible to ensure that the measurement results comply with international standards and specifications, thereby enhancing the authority and credibility of the measurement results.

4、 Improve measurement efficiency

Although increasing the evaluation length may increase measurement time and cost, a reasonable evaluation length can ensure the accuracy and reliability of measurement results. If the evaluation length is too short, multiple measurements may be required to obtain accurate results, which not only increases measurement costs but also reduces measurement efficiency. Therefore, by specifying the minimum evaluation length, measurement efficiency can be improved while ensuring the accuracy of measurement results.

In summary, the requirement of minimum evaluation length for roughness is to reduce the influence of other geometric errors, ensure the representativeness of measurement results, comply with international standards and specifications, and improve measurement efficiency. In practical applications, the appropriate evaluation length and corresponding measurement method should be selected based on specific needs and conditions.