Knowledge
A point spectral confocal displacement sensor measures distance using wavelength-encoded white-light interferometry, while a laser triangulation sensor measures distance by detecting the position of a reflected laser spot on a detector. The core difference: confocal sensors work on any surface — including transparent, reflective and layered materials — while triangulation sensors struggle with transparent or highly reflective surfaces but offer longer measurement ranges at lower cost.
How Each Technology Works
Point spectral confocal (chromatic confocal): A polychromatic light source sends light through a lens system where each wavelength focuses at a different distance. Only the wavelength focused exactly on the surface reflects efficiently back through a pinhole to the spectrometer. The measured wavelength maps directly to distance — no moving parts, sub-micron repeatability. Because light travels down and back through the surface, a single confocal measurement can also resolve multiple surfaces (for example, glass thickness top and bottom).
Laser triangulation: A laser diode projects a spot onto the surface at an angle; a receiver lens images the spot onto a PSD or CMOS line. Surface height changes shift the spot position, which converts to distance. Simple and fast, with ranges from sub-millimeter to meters — but performance depends strongly on surface color, gloss and slope.
Comparison Table
| Criterion | Point Spectral Confocal | Laser Triangulation |
|---|---|---|
| Transparent / glass surfaces | Measures through them; resolves thickness layers | Problematic — signal penetrates or scatters |
| Highly reflective (polished metal) | Stable, coaxial optics | Spot glare and multipath errors |
| Rough / diffuse surfaces | Works | Works (best case for triangulation) |
| Repeatability | Sub-micron class (e.g. 3 nm repeatability on POMEAS high-end models) | Micron class typical |
| Measurement range | Typically mm-class (e.g. up to ~35 mm on standard models) | mm to meter class — much longer range available |
| Spot size | Very small (e.g. 17 μm on POMEAS 100 nm-class models) — deep holes and fine features | Small, but larger on long-range models |
| Measurement angle tolerance | High — works at steep incidence angles | Limited — accuracy degrades with tilt |
| Speed | High (spectrometer-limited, kHz class) | Very high |
| Cost | Higher | Lower |
| Best for | Glass, films, polished metals, small features, thickness | General-purpose displacement, longer ranges, rough surfaces |
Decision Rule
- Measuring glass, film, transparent or layered materials → point spectral confocal (triangulation cannot cleanly separate the surfaces)
- Polished, reflective machined parts with sub-micron tolerance requirements → point spectral confocal
- Rough surfaces, longer range (tens of mm to meters), budget-sensitive → laser triangulation
- Deep bores, tiny grooves, steep walls → point spectral confocal (μm-class spot + wide acceptance angle)
POMEAS Point Spectral Confocal Line
POMEAS offers point spectral confocal displacement sensors across multiple range and precision grades — from 3 nm repeatability controllers to models with up to 35 mm range, and compact probes with 17 μm spot size for micro-feature measurement. The 8055 model also integrates with the POMEAS IMAGE 3 MAX measuring system for height measurement.
FAQ
Can a confocal sensor measure glass thickness?
Yes. Because each wavelength reflects from each optical interface, one point spectral confocal measurement can resolve both the top and bottom surface of transparent materials, giving thickness directly.
Which sensor works better on polished metal?
Point spectral confocal. Its coaxial optical design avoids the spot-glare errors that affect angled laser triangulation on shiny surfaces.
Is laser triangulation ever the better choice?
Yes — for rough, diffuse surfaces and when the required range exceeds the mm-class window of confocal sensors, triangulation is more cost-effective.
Subscribe to Our Newsletter
Simply enter your email to receive the latest news and insights from Pomeas. Stay connected with Pomeas and be the first to discover new innovations in optical excellence.
