Mechanical Measurement and Metrology

1.Akash Parmar(140210125075) 2.Mit Shah(140210125112)

3.Ashish Soni(140210125117) 4.Harshil Sutariya(140210125118)

Basics of optical interference and interferometry

Optical flat 1) Flatness checking by optical flat 2) Surface contour test 3) Checking of parallelism by optical flat Interferometers 1) The N.P.L. flatness interferometers 2) The pitter N.P.L gauge interferometer Opto-electronic measurements

Basics of optical interference and interferometry

Interference :- Interaction of light wave. Interferometers :- The instruments designed to measure with interference.

Optical flat

The Essential equipment for measurement by light wave interference is a monochromatic light source and set of optical flat.

Circular optical glass. Quartz having two plates. Cylindrical pieces have 25 to 300 mm diameter. Thickness is (1/6) of dia. Optical flats used in area where temp. is constant.

The N.P.L. flatness interferometer

Light sources lens mirror

collimating lens reflectors

optical flat surface to be tested

eye piece glass plate reflector

working

Checking flatness of objects

The Pitter N.P.L. gauge interferometer

The pitter N.P.L. gauge interferometer

This instrument is also known as the NPL type ‘length interferometer’. It is used for determining actual dimensions or absolute length of the gauges . Fig. shows the schematic arrangement of this interferometer . The light from the sources falls

on slit through condensing lens . After collimation by lens , it goes through constant deviation prism whose rotation determines

wavelength passed through reference optical flat to upper surface of gauge block and base plate with it is wrung .

Light is reflected back in mirror and is patterns are observed through a telescope . The optical flat is adjustable for inclination in two planes . So that pitch and direction of the

interference fringes may be set to the best position . The gauge on this instrument will be absolutely flat and parallel and hence the bands on the

gauge top and the base will be of the same pitch and dire, but relatively displaced from other .

This dis. Is recorded for each colour as a fraction of the pitch o the fringes and is used for calculation of the length of the gauge .

Opto-electronic measurement

Opto-electronic measurement tech is a contactless method . It utilises photodiode arrays having resolution.

Fig shows the arrangement of simple opto-electronic inspection system. The object to be inspected is back-illuminated by collimated light source A lens assembly is incorporated to provide either magnification for

dimensional inspections or reductions for flaw detection . Here we use 45 degree prisms in order to reduce the space

requirements and all components are mounted on a precision slide to form an integral station of and inspection machine .

Opto-electronic measurement

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