GB/T 40742.1-2021Geometrical product specifications (GPS)—Geometrical precision verification—Part 1: Basic concept and measurement—Symbol, terminology, measuring conditions and procedures (English PDF)

3.5 Measurement procedure

A detailed description of a measurement, based on the measurement model and the calculations required to obtain the measurement results, according to one or more measurement principles and the given measurement method.

Note 1: The measurement procedure is usually written in sufficient and detailed documentation for the operator's convenience.

Note 2: The measurement procedure may include a statement about the target uncertainty of measurement.

Note 3: The measurement procedure is sometimes referred to as Standard Operation Procedure (abbreviated to SOP). [Source: JJF 1001-2011, 4.6]

6.1 General

The geometric precision verification objects involved in this document are mainly size, shape, orientation, position and surface structure. During the measurement, each measurement process shall be planned, validated, implemented, documented and controlled, and the influence quantities that affect the measurement process shall be identified and considered.

The complete specification of each measurement process shall include all relevant measuring equipment identification, measurement procedures, measurement software, conditions of use, operator capabilities and other factors affecting the reliability of the measurement results, where the measurement procedure shall be written in sufficient and detailed documents to guide the operator to carry out the measurement.

6.2 Measurement process design

6.2.1 General

The measurement process design shall be carried out according to the requirements of the user, the organization and the laws and regulations. The content of measurement process design mainly includes:

-- Definition of the measured object and the measurement task;

-- Definition of the expression form and accuracy requirements of measurement results; […]

6.2.5 Measurement results and verification

Operate according to the actual inspection operation set, to obtain the measurement results, which shall include the measured value of geometric error and the uncertainty of measurement. See GB/T 18779.2 for the evaluation, expression and management specifications of uncertainty of measurement; perform a conformity assessment according to the measurement results and the tolerance specification of the measured feature, as shown in GB/T 18779.1.

6.3 Specification and implementation of the measurement process

The specification of the measurement process needs to comply with the following requirements during the implementation process:

a) The measurement shall ensure that the measuring equipment, environmental conditions and fixtures meet the relevant regulations in the measurement model;

b) The measurement personnel shall understand the measurement target, measurement scheme, and be familiar with the operation of the measuring equipment;

c) Before the measurement is carried out, it is necessary to ensure that the preparations for the measurement - such as the preheating and calibration of the equipment, import of the measurement model data - are completed;

d) The measurement operation process shall follow the corresponding measurement specifications; the use of the measuring equipment shall be carried out in accordance with the instrument manual;

e) During the measurement, in consideration of the fluctuation of the environment (temperature, humidity, etc.) over time, monitoring measures shall be taken to ensure that the environmental conditions are always within the allowable working range of the measuring equipment;

f) Statistical analysis shall be carried out for the measurement results, so as to detect deviations caused by measurement or process in a timely manner;

g) The uncertainty of measurement, which is a parameter associated with the measurement result, shall be analyzed and evaluated.

6.4 Standardization of the measurement method

To ensure that the measurements are carried out in the same way, the measurement method shall be standardized, and all measurements shall be carried out according to the specified standard methods. There shall be a written document specifying all the details of the measurement to be carried out, including how to obtain and prepare the test piece.

The measurement method shall be a standardized and robust method, that is, the measurement results will not produce unexpected large changes to small changes in the measurement process. If there is a large change in the measurement process, appropriate precautions shall be taken or a warning shall be issued. In developing a standard measurement method, efforts shall be made to eliminate or reduce the offset of measurement data.

Some similar test procedures can also be used to test the correctness and precision of established and newly standardized measurement methods, where the results obtained from the latter case should be considered as initial estimates, because the correctness and precision vary with the accumulation of laboratory experience.

The documentation for establishing the measurement method shall be clear and complete. All the important operations involving the procedure's environment, reagents and equipment, initial inspection of equipment, and preparation of test samples shall be included in the measurement method. Measurement results and calculations, as well as the number of significant figures shall be clearly stated. […]