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Mechanical Measurement and Metrology

Veröffentlicht in: Ingenieurwesen


  2. 2. Contents • Introduction • Basic Principle • Uses • Characteristics • Classification • Mechanical Comparators And Its Types • Mechanical-Optical Comparators • Electrical Comparators • Pneumatic Comparators
  3. 3. Introduction • Comparator is a precision instrument • Employed to compare the dimension of given component with given standard • Employed to find out, by how much the dimensions of the given component differ from that of a known datum.
  4. 4. Basic Principle • Initially, the comparator is adjusted to zero on its dial with a standard job in position. • The reading H1is taken with the help of a plunger. • Then the standard job is replaced by the work-piece to be checked and the reading H2 is taken. • If H1and H2 are different, then the change in the dimension will be shown on the dial of the comparator.
  5. 5. Uses Of Comparators • Comparators can be used as: 1. Laboratory Standards 2. Working Gauges 3. Final Inspection Gauges 4. Receiving Inspection Gauges 5. For Checking Newly Purchased Gauges
  6. 6. Characteristics 1. Robust Design and Construction 2. Linear Characteristics of Scale 3. High Magnification 4. Quick in Results 5. Versatility 6. Minimum Wear of Contact Point 7. Free from oscillations and back lash 8. Quick Insertion of Work piece 9. Adjustable table 10.Compensation from Temperature Effects 11.Means to Prevent Damage
  7. 7. Classification 1. Mechanical comparators • Dial Indicator • Reed Type comparator • Sigma Comparator • Johansson Mikrokator 2. Mechanical Optical Comparators • Optical Lever • Zeiss Optimeter • Zeiss Ultra Optimeter • Zeiss Optotest Comparators 3. Electrical and Electronics Comparators 4. Pneumatic Comparators
  8. 8. 5) Fluid Displacement Comparators 6) Projection Comparators 7) Multi check Comparators 8) Automatic Gauging 9) Electro Mechanical Comparators 10) High Sensitive Calibration Comparators • Brookes Level Comparators • Eden-Rolt Millionth Comparators Classification
  9. 9. • Self controlled and no power or any other form of energy is required • It employs mechanical means for magnifying the small movement of the measuring stylus • The movement is due to the difference between the standard and the actual dimension being checked Mechanical Comparators
  10. 10. 1. Dial Indicator
  11. 11. 1. Dial Indicator • Amplifies the length or displacement and translate it into rotational motion of pointer over circular scale • Applications:- 1. To compare two heights or distance between narrow limits 2. For determining errors in geometrical forms 3. For testing alignment, roundness and parallelism of work piece 4. For quality control and inspection work
  12. 12. 2.Johannson mikrokator • Principle  When a tension is applied to the twisted strip, it causes the strip to untwist resulting in rotation of pointer which is attached at centre of the twisted strip
  13. 13. 2.Johannson mikrokator
  14. 14. 3.Reed Type Mechanical Comparator •A reed type comparator uses the frictionless reed mechanism for magnifying small motions of spindle •In the following figure: 1. A - Fixed Block 2. B- Floating Block 3. C- Reeds
  15. 15. 4. Sigma Comparator • Principle  Works on leverage principle in which high magnification is obtained
  16. 16. 4. Sigma Comparator
  17. 17. Mechanical Comparators • Advantages 1. Do not require any external source of energy 2. Cheaper and portable 3. Robust construction and compact design 4. The simple linear scales are easy to read 5. Unaffected by variations due to external source of energy such air, electricity etc • Disadvantages: 1. Range is limited as the pointer moves over a fixed scale 2. Pointer scale system used can cause parallax error. 3. There are number of moving parts which create problems due to friction, and ultimately the accuracy is less 4. The instrument may become sensitive to vibration due to high inertia
  18. 18. Mechanical-Optical Comparators •Principle: It works based on fundamental optical law as the edge of the shadow is projected on a curved graduated scale to indicate the comparison measurement.
  19. 19. • Advantages:- 1. Less friction and inertia effect and higher accuracy 2. High magnification 3. Enables readings to be taken irrespective of room lighting conditions 4. High range and no parallax • Disadvantages:- 1. Requires light source 2. Large and expensive 3. Inconvenient for continuous use 4. Instrument setting may drift Mechanical-Optical Comparators
  20. 20. Electrical Comparator • Principle:- Operation depends on an AC Wheatstone bridge circuit incorporating a galvanometer.
  21. 21. Electrical Comparator
  22. 22. Pneumatic Comparators • Principle:-  The change in pressure between nozzle and work piece is utilized to measure the deviation of the dimension being measured from the standard dimension.
  23. 23. Pneumatic Comparators
  24. 24. • Advantages:- 1. Very high magnification 2. Less friction, wear and inertia 3. Less measuring pressure 4. Determines ovality and taperness of circular bores • Disadvantages:- 1. Scale is generally not uniform 2. Requires compressor and accurate pressure regulator 3. Non portable 4. Less sensitivity Pneumatic Comparators
  25. 25. Thank You 