Thickness measurement using Conoscopic Holography non-contact laser sensors

Using non-contact laser sensors can provide the end users a variety of parameters to measure and characterize surface features such as flatness, roughness, and displacement. One dominant parameter end users want to measure is the thickness of metal, plastic, wood, and glass. In this blog we discuss thickness measurement of diffusive materials. Another blog will discuss thickness measurement of glass and transparent materials, which is more challenging and needs to consider material coefficients.

Optimet laser sensors are co-linear, meaning the laser exits and returns from the sensor on the same optical axis. This allows the use of two sensors which can be aligned to each other perpendicularly to a surface to perform a thickness measurement, as shown below.

One sensor can be set above the sample, while the other one exactly below. After the two sensors have been aligned, thickness measurement is straight forward and simple. Each sensor provides the absolute distance to the sample, and can be the reference measurement of the other sensor.

First we use a metrological block of known thickness as a reference

The block placed on the measurement axis, inside both probes measurement ranges as described in the draw above. Using both probes measurements, we created the reference distnace Z0 :

Now, by using this formula we can extract the sample thickness.

When measuring thickness of diffusive material, no cross-talk exits like for transparent materials.

Any of Optimet’s diffusive sensors can perform the measurement including the CP-3, CP-10 and CP-20, used for fastest measurement rate.

Triangulation sensors are not suitable for this application since the laser is not co-linear and can’t be placed on the same axis. The measurement concept is very clear in this video:

Contact us for more information on your particular application challenge.

 

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