Analysis of the difference and relationship between "equal" and "level" in measuring blocks

Definition of measuring blocks

The measuring block is a physical measuring tool made of wear-resistant material, with a rectangular cross-section and equipped with a pair of parallel measuring surfaces. These measuring surfaces can not only be combined with each other for use, but also with auxiliary bodies with similar surface quality for precise measurement of the length of the measuring block.

The shape of the measuring block

The shape of the measuring block is shown in Figure 3. Among them, the top and bottom respectively refer to the measuring surface, while the front, back, left, and right describe the various sides of the measuring block. Each measuring block has two measuring surfaces and four side surfaces. For measuring blocks with a nominal length not exceeding 5mm, the number representing the nominal length will be engraved on the upper measuring surface, opposite to the lower measuring surface. For measuring blocks with a nominal length exceeding 5mm, the number representing the nominal length will be engraved on the larger side area. When the side is placed in a forward direction (as shown in Figure 3), the right side is the upper measuring surface, and the left side is the lower measuring surface.

The division of "equal" and "level" in measuring blocks

The reason for dividing measuring blocks into "levels"

In order to meet the requirements of different measurement accuracies while considering economy, manufacturers classify measuring blocks into different levels based on indicators such as flatness, fit, length variation, and manufacturing deviation. Gauge blocks with small deviations are selected as high-level, while those with large deviations are selected as low-level to meet various measurement accuracy requirements. When leaving the factory, the measuring block is only labeled with its complete set of levels, and users only need to use it according to the nominal value.

02 Consideration of dividing measuring blocks into "equal" sections

With the increasing demand for length measurement accuracy in industry and defense research, the measurement level of measuring blocks urgently needs to be improved. In order to solve this contradiction, high-precision measurement methods were introduced to determine the actual size of the gauge block, that is, to determine its deviation from the scale size. During use, users can make corrections based on the actual size or deviation to meet the high-precision measurement requirements.

In addition, the quality of the working surface of the measuring block may be damaged during use, such as scratches, wear, etc. When these damages reach a certain level, the measuring block needs to be repaired. The length of the repaired gauge block may be shortened or even exceed the allowable deviation of the original level. At this point, although the measuring block will be downgraded for use, its value will not be affected. However, if used according to the principle of "equality", as long as the key indicators such as flatness, compatibility, and length variation of the measuring block can be restored to meet the requirements of the original equality after repair, even if its length deviation has increased and degraded, it can still be verified according to the original equality verification method and retain its original level. In this way, the service life of the measuring block is effectively extended. Therefore, from a usage perspective, dividing measuring blocks into "equal" is an important measure to ensure their accuracy in use.

The association between the "equal" and "level" of measuring blocks

The "equal" and "grade" of measuring blocks are two different ways of dividing their accuracy during the verification and manufacturing process. They follow different division principles and usage rules, but are closely related to each other. According to the provisions of JJG146-2011 "Calibration Regulations for Measuring Blocks", we have made clear divisions and definitions for it.
Gauge blocks are classified based on the measurement uncertainty of their length. When measuring the length of a measuring block with precision, the uncertainty of the measured value will be indicated based on the measurement accuracy. By comprehensively considering the measurement error of the length of the gauge block and other technical indicators, the gauge block is divided into "equal" processing. Therefore, the concept of "waiting" reflects the degree of closeness between the measured length value of the gauge block and its true length value, that is, the allowable error range of the measurement accuracy of the gauge block. In China, measuring blocks are divided into five levels, with level 1 beinghighgrade
The deviation of the length of the measuring block is an important basis for dividing its level. The concept of "level" actually reflects the degree of closeness between the measured length of the gauge block and its nominal length, that is, the allowable error range during the manufacturing process of the gauge block. In China, measuring blocks are divided into five levels: K and 3, with the accuracy level of level K being the highesthigh.
According to the JJG146-2011 "Calibration Regulations for Gauge Blocks", when conducting "grade" calibration on gauge blocks of different grades, the level of length measurement uncertainty should meet the requirements in Table 1. Specifically, the measurement uncertainty of K-level gauge blockslowWaiting for level 1 (2), while for level 0, level 1, level 2, level 3, and level 5 gauge blockslowThey are 2 and 0 respectively. These regulations ensure the accuracy and quality of measuring blocks during manufacturing and calibration processes, thereby ensuring the accuracy and reliability of measuring blocks as standard measuring tools in the field of measurement.
According to JJG146-2011 "Calibration Regulations for Gauge Blocks", when conducting "equal" calibration, the initial level of the gauge block shall not be lower than the provisions listed in Table 2. Specifically, at the beginningtimeThe grade of the measuring block to be verified and the requirements that the measuring block should possesslowThe initial level correspondence is as follows:

• Start with onetimeWhen the grade of the calibration gauge block is 1, the gauge blocklowThe initial level that should be possessed is K.

• Start with onetimeWhen the grade of the calibration gauge block is 2, the gauge blocklowThe initial level that should be possessed is 0.

• Start with onetimeWhen the grade of the proposed calibration gauge block is 3, the gauge blocklowThe initial level that should be possessed is 1.

• Similarly, different grades of measuring blocks have their corresponding valueslowInitial level requirements.

These regulations aim to ensure the accuracy and reliability of measuring blocks during the calibration process, thereby guaranteeing their application quality in the field of measurement.
During long-term use and repair, the center length of the measuring block may decrease, exceeding the allowable deviation of the center length specified in the original grade. However, if the measurement uncertainty of compatibility, flatness, length variation, and center length of the gauge block does not decrease or remain unchanged, then the gauge block will only degrade rather than downgrade, resulting in phenomena of high and low levels, such as 2nd grade 1st, 2nd grade 2nd, 3rd grade 2nd, 3rd grade 3rd, etc. In specific use, you can choose the appropriate measuring block according to "wait".
In addition, there is also a substitution relationship between the "equal" and "level" of the measuring block. Specifically, the allowable deviation of the center length of level 2 gauge blocks is equivalent to the measurement uncertainty of level 5 gauge blocks, and their flatness, compatibility, and length variation requirements are also higher than or equal to those of corresponding level gauge blocks. Therefore, in practical applications, level 2 measuring blocks can be used to replace level 5 measuring blocks respectively. However, it should be noted that 3rd and 5th grade blocks cannot replace 0th and 2nd grade blocks due to their lower requirements for flatness, compatibility, and length variation.

There are usually two options for using measuring blocks. One is to use it according to the "equal" category, that is, to analyze and calculate based on measured values or deviation values, which requires consulting the calibration certificate and accurately calculating according to the measurement uncertainty of that category. Although it can improve measurement accuracy, the operation is relatively complex. Another option is to use according to the "grade", that is, to directly measure and analyze the nominal value of the measuring block without consulting the calibration certificate. Due to the inclusion of manufacturing deviation in the nominal value, its measurement accuracy may be slightly lower than the method used according to "equal", but the operation is more convenient.