Measurement by Pitter - N.P.L. Gauge interferometer - Metrology & Quality Control

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• Sravanthi   -Posted on 26 Oct 15
  - The Pitter - N.P.L. Gauge interferometer NPL gauge interferometer is known as NPL type length interferometer. NPL flatness interferometer is used to measure flatness.
  
  - It is used to measure actual length of gauges.
  
  - Mercury or cadmium lamp is used as the light source in this instrument. Four wavelengths of each lamp are obtained.
  
  
  Mercury lamp:
  
  a) In these sources discharge lamp is charged with an element and this can be vaporised. They emit radiations at certain wavelengths as these are excited electrically. They are less expensive and have high intensity.
  
  b)The green line obtained is easily isolated with filters. Natural mercury contains isotopes and they emit different wavelengths which are slightly different from each other.
  
  
  Cadmium
  
  a)Two yellow, one green, one violet light is obtained by mercury lamp and cadmium lamb gives one red, one green, one blue and one violet light.
  
  b)This material produces spectral line which is symmetrical and has path difference of 200 mm.
  
  c) Cadmium 114 is considered as secondary international standard of length.
  

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