Dimension measurement


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Dimension measurement

  2. 2. Presentation on DIMENSION MEASUREMENT Presented to: Dr. –Ing. Naveed Ramzan Presented by: Noor Ul Ain Sabir 2008-CHEM-09
  3. 3. Contents 1. Dimension measurement • Why to measure dimensions 2. Thickness measurement • Thickness gauges 3. Length measurement • Laser based length measurement 4. Width measurement • Camera based width measurement 5. Diameter measurement • Laser based diameter measurement REFERNECES 3
  4. 4. 1. Dimensionmeasurement The determination of linear and angular magnitudes of particular features or mechanical parts of a prototype or machine itself is called as Dimension Measurements. 4
  5. 5. Why to measure dimensions??? Dimension measurement and regulations are among the quality control parameters of industrial machinery design. This practice is done to • Meet the customer’s requirements • Avoid any deviation in dimensional tolerances • Avoid rejection of the product by the customers 5
  6. 6. Dimensional requirements The following parameters of an object are normally measured or determined in routine: • Thickness • Length • Width • Diameter 6
  7. 7. 2. Thickness measurement In some industrial productions the control or measurement of thickness of coating, applied to a base material is essential e.g. • Deposition of zinc on steel • Application of wax, clay bitumen or plastic on paper etc. This base or sheet material thickness measurement with and without coating material is done with the help of a device known as ‘thickness gauge’. 7
  8. 8. 8 Thickness gauges Contact type gauges Inductive type Capacitive type Non-contact type gauges Radiation type Laser based Coating gauges Differential beta gauge Beta backscatter gauge
  9. 9. Thickness gauges a. Contact type thickness gauges i. Inductive type • Reluctance transducer • Eddy current transducer ii. Capacitive type b. Non-contact type thickness gauges i. Radiation type ii. Laser based c. Coating thickness gauges i. Differential beta thickness gauge ii. Beta backscatter thickness gauge 9
  10. 10. a. Contact type thickness gauges Here we find that • Thickness of the object is found through electrical methods. • The gauges make measurements upon a physical contact with the test piece 10
  11. 11. i. Inductive type thickness gauge Two kinds of transducers are utilized: • Reluctance variation transducers: These devices measure change in inductance of a magnetic coil caused by the test object. • Eddy current transducers: They use eddy currents to find the thickness of test object. 11
  12. 12. Reluctance variation transducer • It consists of a U-shaped magnetic core over which a coil is wound .The stock or a test piece, whose thickness is to be measured, completes the magnetic circuit. • Inductance of the coil depends upon the reluctance of the magnetic circuit, which in turn depends upon the thickness of the test object
  13. 13. Reluctance transducer 13
  14. 14. Reluctance transducer
  15. 15. Reluctance transducer • The non-magnetic test piece is placed on ferromagnetic base; the base is thick such that the reluctance of the magnetic circuit is determined by the distance between the ends of the U-core and the base plate. • An increase in thickness of the test piece causes an increase in reluctance and a decrease in inductance of the magnetic circuit.
  16. 16. Eddy current transducer* (Conducting material) • It has a coil wounded on an insulated core, excited by an alternating current supply. The alternating field produced as a result generates eddy current in the test piece. • The opposition created by the magnetic field of eddy current against the magnetic field of coil, reduces the inductance of the coil. • So, higher the thickness of the test piece, higher will be the eddy current, lower would be the inductance of the coil.
  17. 17. Eddy current transducer 17
  18. 18. Eddy current transducer (Non-Conducting) • For non-magnetic, non-conducting materials thickness measurement is done by depositing it on a metal backing. • If the thickness of the test piece is large, the eddy current transducer head and the metal backing are separated by a larger distance and, therefore, the eddy currents are small and consequently the inductance of the coil is large.
  19. 19. Eddy current transducer
  20. 20. Inductive type gauges • Advantages - Measurement of thickness of aluminum sheet 125-500 pm - Easy to align - Excellent repeatability • Disadvantages - Physical contact causes error in measurement - It shows temperature sensitivity - Inherently low power output 20
  21. 21. ii. Capacitive type thickness gauge • This method is used for the thickness measurement of insulators. C = capacitance in farad Ɛ0= 8.85 x 10-12 farad/m2 Ɛr = dielectric constant (relative permittivity) A= area of each plate (m2) d= distance between the plates (m) 21
  22. 22. Capacitive thickness measurement 22
  23. 23. Capacitive type gauges • Advantages - Their frequency response is good. - They require little force for operation. • Disadvantages - They are sensitive to temperature changes, - They become contaminated with dust particles 23
  24. 24. b. Non-contact thickness gauges They measure the thickness without physical contact and are of following three types i. Radiation type ii. Laser based 24
  25. 25. i. Radiation type non-contact gauge • These gauges employ alpha, beta, gamma or X-ray radiation obtained from a radioactive element for thickness measurement. • The radiation source is shielded all around except in the direction of the detector. • The radiation source radiates to the detector through the test object. • The radiation received at detector are amplified and calibrated to find the thickness of object. 25
  26. 26. Radiation type non-contact gauge 26
  27. 27. Radiation type non-contact gauge • Advantages - It gives the thickness measurement of sheets in rapid motion without physical contact. • Disadvantages - These are subjected to error because of radioactive decay of source and dependence of absorption coefficient on the composition of material - Frequent calibration checks are required for better accuracy. 27
  28. 28. ii. Laser based non-contact gauge • These gauges employ a laser beam. • The beam is directed at a rotating (or oscillating) mirror to collimate in to a straight ribbon. • As the collimated beam scans across an object, it blocks the light detector on the other side and measures the time for which the light was blocked. Thus, scan time across the shadow is used to measure the thickness of an object. 28
  29. 29. Laser based non-contact gauge* 29
  30. 30. c. Coating thickness gauges To measure the thickness of coating materials, two types of gauges are used i. Differential beta gauge ii. Capacitive sensor for measuring coating thickness 30
  31. 31. i. Differential beta gauge This technique involves two beta gauges. • The readings are obtained by passing the un-coated sheet through one measuring head and the coated from the other. The intensity of radiation emitted is a measure of total thickness. • They found application in the measurement of thickness of wax and plastic coatings applied to paper and aluminium sheet when the weight of coating is 25% or more of the weight of substrate. 31
  32. 32. Differential beta gauge* 32
  33. 33. 3. Length measurement Laser Doppler Velocimeters (LDVS) • The laser Doppler velocimeter sends a monochromatic laser beam towards the target and collects the reflected radiation. • According to the Doppler Effect, the change in wavelength of the reflected radiation is a function of the targeted object's relative velocity. 33
  34. 34. Laser Doppler Velocimeter 34
  35. 35. 4. Width measurement Camera based width measurement is an online non contact technique, using two configurations. • Stereoscopic vision based: It is used where the strip thickness changes substantially. 35
  36. 36. Camera-based width measurement 36
  37. 37. 5. Diameter measurement • It is a laser based system to measure diameter of any type of opaque rod or rounds. • The laser beam emitted from the laser diode in the transmitter is converged into a parallel beam by the projecting lens unit. • The laser beam is then directed through the slit on the receiver and focused on the light receiving element. 37
  38. 38. Laser Diameter gauge* • Construction and working - The gauge consists of two diameter measuring sensors which are kept such a way to measure axes of the rod at tow angles of interest. - The laser transmitter-receiver pairs are kept facing each other at some distance. When a test rod is passed through the measurement area, the light falling on the receiver will reduce, in the amount of diameter of the rod. 38
  39. 39. Laser diameter gauge 39
  40. 40. Laser diameter gauge Advantages • Non-contact type • Online measurement of diameter • Versatile and provide accurate measurements
  41. 41. Summary • Dimension measurement is required to assure top quality of products as per customer specifications. • Thickness gauges can be of Contact and Non-contact type and use inductance, capacitance, laser technology and beta radiations for measuring the thickness of base materials and applied coating surfaces. • The length of an object can be found by subjecting it to a laser source and thus noticing the shift in frequency of laser beam.
  42. 42. Summary • The width of object can be found by employing Stereoscopic vision principle. • The diameter of an object is found using laser transmitter and receiver arrangement, the decrease in intensity of radiations received is a direct measure of diameter.
  43. 43. Questions 43
  44. 44. REFERENCES • Singh. S.K. 2009. Industrial instrumentation and control, 3rd Edition, McGraw Hill publishing company limited, New Delhi; 225-238 • www.ldvsysteme.de • www.weldedtubepros.com • http://www.youtube.com/watch?v=zJ23gmS3KHY • http://www.youtube.com/watch?v=Ucf2TAKPbPA • http://www.youtube.com/user/laplaser 44
  45. 45. 45