Typically, inspecting welds is a visual task, but in particular circumstances it may be critically important to investigate weld profiles with a more extreme level of precision. Specific areas of interest for precise analysis include surface cracks, porosity and unfilled craters, regardless of subsequent inspection procedures. Weld characteristics such as dimension/shape, volume, roughness, size, etc., can all be measured for critical evaluation.

3D Non-Contact Profilometer —Unlike other techniques, such as touch probes or interferometry, the Nanovea 3D Non-Contact Profilometer, using axial chromatism, can measure nearly any surface. Sample sizes may vary widely due to open staging, and there is no sample preparation needed.

The nano- through macro-range readings are obtained during surface profile measurement with zero influence from sample reflectivity or absorption, and the Profilometer has an advanced ability to measure high surface angles. Also, there is no software manipulation of results.

It’s possible measure any material easily: transparent, opaque, specular, diffusive, polished, rough, etc. The technique of the Non-Contact Profilometer provides an ideal, broad, and user-friendly capability to maximize weld surface studies with the benefits of combined 2D & 3D capability and portability for field studies.

In this application the Nanovea ST400 Profilometer is used to measure the surface roughness, shape, and volume of a weld, as well as the surrounding area. This information can provide critical information to properly investigate the quality of the weld and weld process.

Measurement Principle —The axial chromatism technique uses a white light source, where light passes through an objective lens with a high degree of chromatic aberration. The refractive index of the objective lens will vary in relation to the wavelength of the light. In effect, each separate wavelength of the incident white light will re-focus at a different distance from the lens (different height).

When the measured sample is within the range of possible heights, a single monochromatic point will be focalized to form the image. Due to the confocal configuration of the system, only the focused wavelength will pass through the spatial filter with high efficiency, thus causing all other wavelengths to be out of focus. The spectral analysis is done using a diffraction grating. This technique deviates each wavelength at a different position, intercepting a line of a charge-coupled device (CCD), which in turn indicates the position of the maximum intensity and allows direct correspondence to the Z height position.