This standard applies to the initial calibration, subsequent calibration and in-use inspection of external micrometers with a graduation value of 0.01mm and an upper measurement limit of 500mm; plate thickness and wall thickness micrometers with an upper measurement limit of 25mm; and digital external micrometers with a resolution of 0.001mm, 0.0001mm and an upper
measurement limit of 500mm. JJG 21-2008 Micrometer Calibration Procedure JJG21-2008 Standard Download Unzip Password: www.bzxz.net This standard applies to the initial calibration, subsequent calibration and in-use inspection of external micrometers with a graduation value of 0.01mm and an upper measurement limit of 500mm; plate thickness and wall thickness micrometers with an upper measurement limit of 25mm; and digital external micrometers with a resolution of 0.001mm, 0.0001mm and an upper measurement limit of 500mm.

This regulation refers to the following documents:
JJF1001—1998 General metrological terms and definitions
JJF1059—1999 Evaluation and expression of measurement uncertainty
JJF1094—2002 Evaluation of measuring instrument characteristics
GB/T1216—2004 Outside micrometer
GB/T20919—2007 Electronic digital outside micrometer
JB/T2989—1999 Plate thickness micrometer
When using this regulation, attention should be paid to using the currently valid versions of the above-mentioned references.
1 Scope (1)
2 References (1)
3 Overview (1)
4 Metrological performance requirements (3)
4.1 Axial play and radial runout of the micrometer screw (3) 4.2
Relative offset between the measuring anvil and the measuring surface of the micrometer screw (3) 4.3
Measuring force (3)
4.4 Scale width and width difference (3)
4.5 Relative position of the pointer and the dial (3)
4.6 Distance from the end face edge of the differential cylinder cone to the scaled surface of the fixed sleeve (3)
4.7 Relative position of the end face of the differential cylinder cone and the millimeter scale of the fixed sleeve (3)
4.8 Flatness of measuring surface (3)
4.9 Repeatability of indication of digital outside micrometer (3)
4.10 Drift of value at any position of digital outside micrometer (4)
4.11 Parallelism of two measuring surfaces (4)
4.12 Indication error (4)
4.13 Subdivision error of digital outside micrometer (5)
4.14 Calibration rod (5)
5 General technical requirements (6)
5.1 Appearance (6)
5.2 Interaction of various parts (6)
6 Control of measuring instruments (6)
6.1 Verification conditions (6)
6.2 Verification items (6)
6.3 Verification methods (7)
6.4 Processing of verification results (11)
6.5 Verification cycle (11)
Appendix A Evaluation of uncertainty in the measurement results of micrometer indication error (12)
Appendix B Evaluation of uncertainty in the measurement results of digital micrometer indication error (16)
Appendix C Format of the inner pages of the verification certificate and verification result notification (20)

National Metrology Verification Regulation of the People's Republic of China JJG21--2008
Micrometer
Promulgated on March 25, 2008
Implementation on September 25, 2008
Promulgated by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China JJG21--2008
Verification Regulation of Micrometer
Verification Regulation of Micrometer JJG21---2008
Replaces JJG21-1995
This regulation was approved by the General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of China on March 25, 2008, and came into effect on September 25, 2008.
Responsible unit: National Technical Committee on Geometry and Engineering Parameters Drafting unit: Heilongjiang Metrology Verification and Testing Institute Jilin Metrology Science Research Institute
This regulation is entrusted to the National Technical Committee on Geometry and Engineering Parameters for interpretation
Main drafters of this regulation:
JJG21-—2008
Zhang Liping (Heilongjiang Metrology Verification and Testing Institute) Ma Zhonghuan (Jilin Metrology Science Research Institute) Dou Yanhong (Jilin Metrology Science Research Institute) Participating drafters:
Wang Xiaoliang (Heilongjiang Metrology Verification and Testing Institute) Wang Li (Harbin Metrology Verification and Testing Institute)2
Citation Literature
Overview·
4 Metrological performance requirements
JJG21---2008
Axial play and radial swing of micrometer screw·Relative offset between measuring anvil and measuring surface of micrometer screw·
Grade width and width difference
Relative position of pointer and dial
Distance from the end edge of differential cone to the scale surface of fixed sleeve··Relative position of the end face of differential cone and the millimeter scale of fixed sleeve, flatness of measuring surface
Repeatability of indication of digital outside micrometer·Numerical drift at any position of digital outside micrometerParallelism of two measuring surfaces
Indication Error
Digital display outside micrometer subdivision errorWww.bzxZ.net
Calibration rod
5 General technical requirements·
5.1 Appearance·
Interaction of various parts
6 Control of measuring instruments:
Verification conditions:
Verification items
Verification methods
Processing of verification results….
Verification cycle·
Appendix A Evaluation of uncertainty in measurement results of micrometer indication error Appendix B
Appendix C
Evaluation of uncertainty in measurement results of digital display micrometer indication error Format of the inner pages of verification certificate and verification result notice (1)
（3）
（3）
（4）
（5）
（5）
（6）
1 Scope
JJG21—-2008
Micrometer Calibration Procedure
This procedure is applicable to the initial calibration, subsequent calibration and in-service inspection of outside diameter micrometers with a graduation value of 0.01mm and a measuring upper limit of 500mm; plate thickness and wall thickness micrometers with a measuring upper limit of 25mm; and digital outside diameter micrometers with a resolution of 0.001mm, 0.0001mm and a measuring upper limit of 500mm. References
This specification refers to the following documents:
JF1001-1998 "General metrological terms and definitions" JJF1059-1999 "Evaluation and expression of measurement uncertainty" JJF1094-2002- "Evaluation of measuring instrument characteristics" GB/T1216-2004 "Outside micrometer" GB/T20919-2007 "Electronic digital display outside micrometer" JB/T2989-1999 "Plate thickness micrometer" When using this specification, attention should be paid to the use of the current valid versions of the above references. Overview
Micrometer is composed of a ruler frame, anvil,
1, 2, 3, 4, 5, 6.
Force measuring device
locking device and reading device. As shown in Figure 6
Figure 1 The micrometer with fixed anvil
1-Ring; 2-Anvil; 3-Micrometer screw; 4-Locking device, 5-Fixed sleeve 6-Differential cylinder; 7-Force measuring device; 8-Heat deviceFigure 2 The micrometer with replaceable or adjustable anvil 1-Fix screw; 2-Anvil; 3-Ring; 4-Micrometer screw; 5-Heat insulation device, 6-Force measuring device, 7-Differential cylinder; 8 Fixed sleeve; 9 locking device a)
JJG21-2008
Calibration rod
Figure 4 Wall thickness micrometer
1-ruler frame; 2-anvil: 3-micrometer screw; 4-locking device: 5-fixed sleeve 6-differential sleeve; 7-force measuring device 8-insulation board (b)
Figure 5 Plate thickness micrometer
（a）1- Ruler frame; 2-anvil, 3-micrometer screw: 4-locking device; 5-dial; 6-pointer; 7-fixed sleeve: 8-differential cylinder; 9-force measuring device (b) 1-rule frame; 2-measurement brick: 3-micrometer screw: 4-locking device, 5-fixed sleeve: 6-differential cylinder; 7-force measuring device 00.000
Figure 6 Digital outside micrometer
1-rule frame: 2-
micrometer screw; 3-
locking device: 4
fixed device: 5-differential cylinder
6-thermal insulation device: 7-measurement; 8-button; 9-display; 10-force measuring device JJG21-2008
Micrometer is a measuring tool that uses the principle of screw pair transmission to convert rotary motion into linear motion. It is mainly used to measure various external dimensions.
4 Metrological performance requirements
4.1 Axial play and radial swing of the micrometer screw The axial play and radial swing of the micrometer screw shall not exceed 0.01 mm. 4.2 Relative offset between the measuring anvil and the measuring surface of the micrometer screw The relative offset between the measuring anvil and the measuring surface of the micrometer screw shall not exceed the requirements in Table 1. Table 1 Relative offset between the measuring surface of the anvil and the micrometer screw Upper limit of the measuring range
4.3 Measuring force
Offset
Upper limit of the measuring range
200, 225
250, 275, 300
325, 350, 375
400, 450
475, 500
Offset
The measuring force of the micrometer (referring to the force exerted when the measuring surface contacts the spherical surface) should be (510) N. 4.4 Graduation width and width difference
The width of the differential barrel is (0.08～0.20) mm, and the width difference between the scale lines on the fixed sleeve and the scale lines on the differential cylinder should not be greater than 0.03 mm. The width of the scaled dial is (0.20～0.30)mm, and the width difference should not exceed 0.05mm.
4.5 Relative position of pointer and scale
The end of the pointer on the scale of the plate thickness micrometer should cover 30%～80% of the length of the short scaled line of the scaled dial, and the distance from the upper surface of the end of the pointer to the surface of the scaled dial should not exceed 0.7mm. The width of the end of the pointer and the scaled lines of the scale should be consistent, and the difference should not exceed 0.05mm.
4.6 The distance from the end edge of the differential cone to the scaled surface of the fixed sleeve The distance from the edge of the differential cone to the scaled surface of the fixed sleeve should not exceed 0.4mm. 4.7 Relative position of the end face of the differential cylinder cone and the millimeter scale of the fixed sleeve When the lower limit of measurement is adjusted correctly, when the zero scale on the differential cylinder is aligned with the vertical scale of the fixed sleeve, the end face of the differential cylinder and the right edge of the millimeter scale of the fixed sleeve should be tangent. If not tangent, the pressure line should not be greater than 0.05mm and the line should not be greater than 0.1mm.
Flatness of measuring surface
The flatness of the measuring surface of the outside micrometer should not be greater than 0.6um. The flatness of the measuring surface of the wall thickness micrometer and the plate thickness micrometer should not be greater than 1.5um. The flatness of the measuring surface of the digital display outside micrometer should not be greater than 0.3μm. 4.9 Repeatability of digital display outside micrometer3
JJG21-2008
The repeatability of digital display outside micrometer should not be greater than 1um. 4.10 The numerical drift of the digital display outside micrometer at any position should not be greater than 1um/h4.11 Parallelism of the two measuring surfaces
When the locking device of the outside micrometer is firm and loose, the parallelism of the two working surfaces of the micrometer shall not exceed the requirements of Table 2. Table 2 Maximum allowable error of the indication of the outside micrometer and the parallelism of the two measuring surfaces Measuring range/mm
0~25, 25~50
50~75, 75~100
100~125, 125150
150~175, 175~200
200~225, 225~250
250~27 5, 275~300
300~325, 325~350
350~375, 375~400
400~425,
425~450
450~475, 475~500
Maximum allowable error/μm
The parallelism of the two measuring surfaces of the plate thickness micrometer should not exceed 4μm. The parallelism of the two measuring surfaces of the digital display outside diameter micrometer should not exceed the requirements of Table 3. Parallelism of two measuring surfaces/μm
Table 3 Maximum allowable error of the indication of digital external diameter micrometer and parallelism of two measuring surfaces Measuring range/mm
0~25, 25~50
50~75, 75~100
100~125, 125~150
150~175, 175~200
200~225, 225~250
2 50~275，275300
300~325，325~350
350~375，375~400
400~425，425~450
450~475，475~500
4.12 Indication error
Maximum allowable error/μm
The maximum allowable error of the indication of the outside micrometer shall not exceed the provisions of Table 2. Parallelism of two measuring surfaces/μm
JJG21-2008
The maximum allowable error of the indication of the wall thickness micrometer and the plate thickness micrometer shall not exceed ±8um. The maximum permissible error of the indication of the digital outside micrometer shall not exceed the provisions of Table 3. For micrometers with a measurement upper limit greater than 150mm, only the indication error of the micrometer head can be detected. The maximum permissible error of the indication of each point of the micrometer head relative to the zero point shall not exceed ±3μm. 4.13 Subdivision error of digital outside micrometer
The subdivision error of the digital display device of the digital outside micrometer shall not exceed ±2μum. 4.14 Calibration rod
4.14.1 Calibration rod of outside micrometer
The calibration rod of the outside micrometer shall be as specified in Table 4.
Size deviation and variation of dead diameter micrometer calibration measuring rod
Calibration measuring rod nominal size
325，350
425，
Micrometer calibration quantity
Digital display outer diameter
Digital display outer diameter micrometer
Nominal size/mm
25，50
125，150，175
200，225，250
275，300
8888883
The size deviation and variation should not exceed
the effective measuring rod
variation/μm
5 provisions.
Digital display outside micrometer calibration rod ruler deviation single displacement variation
NA MEROLO
Variation/μm
325, 350, 375, 400
425, 450, 475
5 General technical requirements
5.1 Appearance
JJG21—2008
5.1.1 The micrometer and its calibration rod should not have bruises, rust, magnetism or other defects. The scale lines should be clear and uniform. The digital display of the digital display outside micrometer should be clear and complete. 5.1.2 The micrometer should be equipped with a tool for adjusting the zero position. The micrometer with a measurement upper limit greater than or equal to 25mm should be equipped with a calibration rod. The micrometer should have a force measuring device, a heat insulation device and a locking device. The calibration rod should have a heat insulation device. 5.1.3 The micrometer should be marked with the graduation value, measuring range, manufacturer's name (or factory mark) and factory number. 5.1.4 The micrometer and the measuring rod used for calibration for subsequent verification and in-use inspection should not have any appearance defects that affect the accuracy of use.
5.2 Interaction of various parts
The rotation of the differential cylinder and the movement of the micrometer screw should be smooth and without jamming. 5.2.2 The adjustment or loading and unloading of the adjustable or replaceable anvil should be smooth and reliable, and the zeroing and locking devices should be effective.
5.2.3 For micrometers with dials, the needle should move flexibly and without jamming. 5.2.4
The working buttons of digital outside micrometers should be flexible and reliable. 6 Control of measuring instruments
Control of measuring instruments includes initial verification, subsequent verification and in-use inspection. 6.1 Verification conditions
6.1.1 Environmental conditions
The room temperature of the calibrated micrometer and the time for the micrometer to be tested to be at the indoor equilibrium temperature shall comply with the provisions of Table 6. The indoor humidity shall not exceed 70%RH.
Table 6 Indoor temperature and time for the micrometer to be tested to be at the indoor equilibrium temperature Micrometer to be tested
Outer diameter, plate thickness, wall thickness
6.1.2 Verification equipment
Micrometer to be tested
Measuring range/mm
>100～500
～100
>100～200
>200~500
See Table 7 for the main verification equipment.
6.2 Verification items
See Table 7 for the verification items.
Allowable deviation of room temperature from 20℃/℃
Micrometer
Measuring rod for calibration
Time for equilibration temperature
Inspected items
Interaction of components
JJG21-2008
Table 7 Inspection items and main inspection equipment
Main inspection equipment
Axial play and radial
swing of micrometer screw| |tt||Relative offset of the measuring surface of the anvil and the micrometer screw
Graded line width and width difference
Relative position of the pointer and the scaled disk
Distance from the shuttle edge of the end face of the differential cylinder cone to the
fixed sleeve scaled surface
Relative position of the end face of the differential cylinder cone and the fixed
sleeve millimeter scale
Flatness of the measuring surface
Indication of the digital outside micrometer Weight
Numerical drift at any position of digital display outside micrometer
Parallelism of two measuring surfaces
Indication error
Digital display outside micrometer subdivision error
Calibration rod
Lever micrometer
Plate, lever dial indicator or dial indicator
Special dynamometer
Tool microscope
Tool microscope, feeler gauge
Level 2 flat crystal, knife edge ruler
4-level gauge block or corresponding special gauge block
Parallel flat crystal, 4-level, 5-level gauge
block, steel ball gauge
4-level, 5-level gauge block or corresponding
special gauge block
Differential cylinder or 5-level gauge block
Vertical contact interferometer, length measuring
machine, 3-level gauge block
Note: "+" means it should be calibrated, "two" means it can be not calibrated. 6.3 Verification method
6.3.1 Appearance
Visual observation.
6.3.2 Interaction of each part
Manual test and visual observation.
6.3.3 Initial calibration of axial play and radial swing of micrometer screw
Subsequent calibration
In-use inspection
Generally, check the axial play and radial swing of micrometer screw by hand. If there is any objection, it can be calibrated according to the following method.
6.3.3.1 The axial play of micrometer screw is calibrated with a micrometer lever. During calibration, the micrometer lever contacts the measuring surface of the micrometer screw, and applies a force of 3N to 5N in the axial direction of the micrometer screw, as shown in Figure 7. The change in the indication of the micrometer lever 7
is the amount of axial play. JJG21—2008
6.3.3.2 The radial swing of the micrometer screw is also calibrated with a lever micrometer. During the calibration, after the micrometer screw is extended 10mm from the scale frame, the lever micrometer contacts the end of the micrometer screw, and then a force of 2N to 3N is applied in the measuring direction of the lever micrometer, and then the same force is applied in the opposite direction. At this time, the change in the lever micrometer indication value is the radial swing amount. The calibration of the radial swing should be carried out in two directions perpendicular to each other of the micrometer screw. This process is shown in Figure 8. Lever micrometer
Figure 7 Axial
6.3.4 Anvil and micrometer screw
Force direction
Force direction
The relative position of the measuring surface
Micrometer measuring brick
Generally, the micrometer can calibrate the two measuring surfaces
of the measuring rod. The measuring range is
. The offset is measured by the inspection tool. When using
on the flat plate, use the jack to contact and observe its deviation.
Micro screw measurement
upper limit of measurement
lever micrometer
relative offset point of the diameter reduction diagram
~25) mm. The micrometer of 25 mm can be used with the help of a calibration ruler. When the
is not agreed, you can compare it with a feeler gauge with a scale of
25)mm. The external precision opening scale with a measuring upper limit greater than 25mm is calibrated with a special
rod dial indicator: the
is placed on a flat plate, such as
parallel to the working surface, and then the micrometer is measured with a dial indicator. As shown in
, adjust the
micro screw to
00mm micrometer and calibrate it with a
dial indicator.
push the micrometer's
screw and the flat plate
, and then use the ruler frame
to measure the offset of the measuring anvil and the micrometer rod in another direction. The micrometer screw is rotated 90° sideways, and the relative deviation of the measuring surface is obtained according to the above degree. This calibration can also be performed with other special inspection tools. V Jack METROLOG Peach rod dial gauge (percentage gauge) Measuring rod Tested ruler Jack item Figure 9 Diagram of calibration with lever dial gauge on a flat plate 6.3.5 Force measurement Use a special dynamometer with a graduation value not greater than 0.2 N to calibrate. During calibration, make the measuring surface contact with the ball working surface of the dynamometer.
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