Length & Dimensional Metrology


1. Preamble
2. Instruments and artifacts required to be calibrated
3. Instruments/Artifacts recommended for Length laboratory
4. Space required
5.

Manpower required

1. Preamble

In the Introduction to Metrology section we made reference to the development of the unit of length, the metre, and of the massive advances required by industry, especially because of International trade and the sub-contracting of manufacturing and assembly. Dimensional metrology has become critical to the success of these processes and continues to drive the uncertainties lower and lower.

The current standard for length is based on the speed of light. By using frequency stabilized lasers, a system of traceable length measurements has been developed. The instruments are known as laser interferometers. There are various grades of interferometers, with the highest being used in national research institutes, and many others down the accuracy scale. There are also three-dimensional machines known as coordinate measuring machines (CMMs).

However, the bulk of length and dimensional measurements are done using a vernier caliper and/or a micrometer. Laboratory-type vernier calipers incorporate a main scale and a sliding vernier scale which allow readings to the nearest 0.02 mm. This type of vernier can be used to measure outer dimensions of objects using the main jaws, and the inside dimensions using the smaller inverted jaws, and depth by using the stem.

The micrometer uses a screw gauge principle and is used to measure smaller dimensions than the vernier calipers. They also have two scales and are able to measure to a resolution of 0.001 mm. Both verniers and micrometers need special care when using them in high precision applications, as it is easy to make mistakes.

Verniers and micrometers are calibrated using gauge (sometimes referred to as gage) blocks and ring gauges, which, in turn, are calibrated by interferometers. There are many other instruments involved in dimensional metrology (analogue and digital) all working on basically the same systems but measuring other things, such as angle, screw threads etc.

Critical to dimensional metrology is an absolutely flat surface to work on, as close to zero vibration as possible and good temperature control. As usual, procedures play an important part, as it is easy for two metrologists to get two different results even when using the same equipment.

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2.

Instruments and artifacts required to be calibrated

 

 

Sl. No. Item Range (mm) Uncertainty/Accuracy/ Resolution (mm)
1. External micrometers 0-25
25-50
50-75
75-100
100-400
in steps of 25 mm
0.001/0.01
0.001/0.01
0.001/0.01
0.001/0.01
0.001/0.01
2. Vernier caliper, vernier depth gauges, digital vernier caliper, digimatic vernier caliper 0-600 mm
150, 200, 300, 600 mm
Least count:
0.01 mm and 0.02 mm
0.01 mm/ 0.02 mm
3. Dial Gauges (plunger type, Lever type) 0-2 mm
0-10 mm 0-25 mm ±100 μm
&plusmn50 μm
0.001 mm,
0.01 mm,
0.0002 mm
4. Gauge blocks (End standards) All setsM10 to M125 Grade '0', I, and II
5. Long gauge blocks (Length bars) 125 mm to 1000 mm in steps of 25 mm Grade '0', I, and II
6. (a) Angle gauges and (b) Polygons 3` to 90 μ 6, 8, 12 and 72 face ±1 sec to ±3 sec
7. Line standards
(a) Steel scale
(b) Glass scales
(c) Glass graticules
(d) Tape measures
(e) Standard metre bars
0-1000 mm
0-300 mm
0-10 mm
0-50 m
1 m
±0.050 mm
0.01 mm
0.003 mm
0.100 mm
0.010 mm/ 0.005 mm
8. Precision Levels All ranges Sensitivity: 0.2 " to 2 "
9. Surface Roughness Ra, Rmax, Rz, Rt ±5%
10. Roundness 200 mm diameter component ±0.05 μm, 0.1 μm
11. Length & dimensional measuring instruments
(a) Dial gauge tester
(b) Caliper checker
(c) Height gauge
(d) Auto-collimator
(e) Sine Bar
(f) Sine Centre
(g) NC/CNC machines
(h) Length measuring machines
(i) CMMs

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3. Instruments/Artifacts recommended for Length laboratory

 

 

Sl. No. Name of the measuring instrument Quantity Priority
1. Long Gauge Blocks (steel)
Range: 125-1000 mm
Calibration grade as per ISO 3650
1 Set
(125, 150, 200, 250, 300, 400, 500, 600, 800 and 1000 mm )
I
2. Gauge Blocks Set (steel)
Grade 'K' or 'OO' as per ISO 3650
M122 (Set of 122 pieces) I
3. Mike Check Set Steel/ WC2 Grade 'O' M10 (1 Set) (2.5, 5.1, 9.7, 10.3, 12.9, 15, 17.6, 20, 22.8 and 25 mm) I
4. Monochromatic Light Unit 200 mm diameter surface plate with spare lamp (sodium) 1 Set Complete I
5. Dial Gauge Tester
(a) Range : 0-25 mm Least count : 0.001 mm Accuracy : ?0.001 mm
(b) Range : 0-5 mm Least count : 0.0002 mm Accuracy : ?0.2 ?m
1 Set I
6. Computerized Gauge Block Comparator
Model: 826 E
Make: Mahr or equivalent
Measuring Range :
0-175/250 mm Range of Scale : 2000 µm x 1.0 μm
200 µm x 0.1μm
20 µm x 0.01μm
1 Set Complete with temperature sensor, accessories, shield etc. I
7. Mike Check Gauge Block set holder 1 I
8. Optical Parallels
12.00, 12.12, 12.25, 12.37 mm diameter
1 set I
9. Optical Flats 1 set I
10 Check Master
Range : 0-1000 mm
10 mm blocks
Block pitch : 20 mm
Accuracy of block pitch : ± 0.0012 mm
Parallelism of block pitch : 0.001 mm
1 Set I
11. Caliper Checker
Range : 0-600 mm
Accuracy of block pitch : ±0.005 mm
Parallelism of block pitch : 0.005 mm
1 Set I
12 Digital Micro Height Gauge with facility of squareness measurement
Range : 0-600 mm / 0-900 mm / 0-1000 mm
Resolution : 0.0005 mm
1 I
13. Comparator Stand
- Chrome plated column
- Column with 8mm diameter clamping device DIN 876 T, grade 'OO'
1 I
14. Slip Gauge Accessories 0-300 mm/0-600 mm 1 Set I
15. Surface Roughness measuring instrument with
(i) Roughness standard
(ii)Groove depth standard
Model: S8P
Make: Perthen or equivalent
Capable to measure all parameters as per IS/ISO/DIN/JIS
1 Complete I
16. Angle Gauge Blocks (steel)
9 x 50 mm measuring face
Accuracy : ±1 sec of arc or better
1 Set of 13 pcs and a square block and straight edge II
17. Auto-Collimator
Model: Elcomet : 2000 Resolution: 0.05"
1 Set II
18 Optical Computerized Moore Index Table
0-360° with stand and accessories Accuracy : 0.1/0.05"
1 Complete II
19. 12 face Polygon Steel/Glass 1 Set III
20. Laser Interferometer with
-Linear optics
-Angular optics
-Flatness optics
-Squareness optics
1 Set complete (material temperature sensor, air sensor) II
21 Sine table 500 mm Lifting resolution equivalent to 0.1 sec 1 II
22. Electronic Level Range: ±2000 counts ±200 counts
Sensitivity : 1 sec per m (5 counts) 0.2 sec per m (1 count) Base length : 150 mm/100 mm
1 Set II
23. Roundness Measuring Instrument
Mahr MMQ40/ or equivalent/or latest
1 Set III
24. Horizontal Metroscope
Measuring Range: 0-1000 mm Resolution: 0.2 µm with facility for inside and external measurements, screw thread measurements
1 set complete II
25. Accessories
(i) Granite Surface Plate 1000 x 1000 mm Grade 1
(ii) Aids like V Blocks, Magnifying glass, Clamps, Level, Scale, Vernier caliper, Dial gauge etc.
3 nos. I

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4. Space required

 

The size of the laboratory will vary greatly, depending on the amount of work that it is required to do and how many workstations it has. It is likely to vary from 45 m2 up to 90 m2

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5. Manpower required

 

 

Metrologist/ Head : M Sc/ BE/ B Tech degree in
Physics or in any branch of
Engineering
ONE
Technical officer : Diploma in Mechanical/
Instrumentation engineering
THREE
Technician : B Sc with some experience in
measurement and calibration
ONE

Please refer to the Introduction to the metrology section for more information.

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