Question

Which technique is not suitable to measure large diameter parts or large gaps?

(a) Diffraction pattern technique

(b) Scanning laser technique

(c) Photodiode array imaging

(d) Laser triangulation sensor

I got this question in class test.

The query is from Laser Inspection in chapter Machine Vision Systems of Engineering Metrology

Answer 1

Right answer is (a) Diffraction pattern technique

Explanation: Diffraction pattern technique is not suitable for diameters larger than few mm and is used to measure small gaps and small diameter parts. In this method, a parallel laser beam which is coherent is diffracted by a small part, and the resultant pattern is focussed on a linear diode array by a lens.