GB/T 18779.5-2020 in English

GB/T 18779.5-2020, as an important part of the product geometry technical specification (GPS) system, clarifies the evaluation framework of the uncertainty of the test value for the inspection process of indicating measuring instruments. The standard solves the problem of conceptual confusion in uncertainty assessment in traditional inspections by strictly defining measured quantities, test protocols and responsibility criteria.

1. The core role of the detection protocol

The standard emphasizes that the detection protocol must be clearly defined:

• Measured value: the specific metrological characteristics of the instrument (such as indication error)
• Permitted detection instance: the permitted combination of detection equipment and environmental conditions
• Operation set: the calculation method from the original indication to the detection value

Example: In micrometer detection, the protocol may specify the use of a gauge block set as the detection equipment, and the temperature range of (20±2)℃ as the permitted environmental condition.

2. Determination criteria for uncertainty components

Handling of User-Supplied Values

When the instrument requires the user to input compensation parameters (such as material thermal expansion coefficient):

1. The tester must provide the actual value of the parameter
2. The uncertainty of the parameter needs to be included in the test value uncertainty as an independent component
3. If the instrument provides a list of preset options, the option closest to the actual value should be selected

Case: When using a laser interferometer for testing, the uncertainty of the air refractive index compensation parameter needs to be evaluated separately.

Use of alternative testing equipment

When the testing partner proposes to use alternative equipment:

• The calibration uncertainties of both equipment need to be compared
• The alternative equipment can only be used when the uncertainty is ≤ that of the original equipment
• The testing party is still responsible for the final uncertainty

Note: Complex equipment (such as the replacement of coordinate measuring machines) requires additional evaluation of issues such as clamping compatibility and software adaptation.

This standard is modified to adopt ISO 14253-5:2015, and the main technical adjustments include:

• Reference to JJF 1059.1 to replace ISO/IEC Guide 98-3
• Add the adaptation of the Chinese metrological terminology system (JJF 1001)
• Strengthen the applicability description for complex instruments (such as coordinate measuring machines)

This standard and other parts of the GB/T 18779 series together constitute a complete judgment system for GPS measurement and inspection.