Instrumental measurement uncertainty

Good evening.

I have a question on Instrumental measurement uncertainty. I use laser scanner sensor to measure lateral dimension of profile, it sends many data (about 800). The point in the scan is not the same. It changes the first starting point (about 0.5mm up or down) , and returns in the same position every four time.

It has an uncertain about 5mm in the center of the scan, and in extreme scan's point it is more accurate (it has an uncertain about 0.5mm in the last 10 point).

I'm interessed to extimate the dimension of profile intercepted by the scan. The scan doesen't intercept the last 10 point, but it' in the center. If I acquire data from 4 consegutive scan and take the average of the measure of the last point intercepted by the scan in profile, what is the uncertain of the measure? Can I reduce the 5mm uncertain?

If the measurement errors are truly random and distributing approximately as a Gaussian profile, then taking the average of N measurements reduces the fractional error by a factor of the square root of N.

If the errors are systematic (that is, inherent to the instrument and the method of measurement), then taking the average of several measurements will not reduce those errors.

What happens when you measure a profile of a known size repeatedly in the same place? Do the measurements change the same way as with the moving profile? Can you give us an example of actual measurements and the actual size that is measured?

How is the laser position actually measured. Is the scanner controller a physical device (rotating arms etc) Does the reflectivity of what you are scanning vary.

As has been suggested you need to perform a series of tests on a single fixed object and observe the variation in scanned response. From that set of data you may be able to devise a correction algorithm.

Does the scanner response/performance vary when you scan from object-to-space as against from space-to-object. For example, if the object is black and the background is white, is the black-to-white response different from the white-to-black response.

An example of measure is about 220mm. The meausre cange if I move away the profile (this happans because the scan intercept the edge in the center of angular excursion, I think). When I move its on left or right the meausre is stable.