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The object position is important for optimal accuracy in the MLG-2 WebChecker. This position must be calculated so that the overlap of the beams has a gapless energy band and the crossed beams have no blind area.
Influence of discrepancy from ideal object position / influence of object thickness
If you need a very good accuracy it is best to choose a longer distance between transmitter and receiver. In our graphic this would be between d: 1000 mm and d: 2500 mm. This way the area of overlap of the spots is the largest and the sensor can also better compensate for temperature changes and vibrations.
The example shows an object shifted by -30 mm to the receiver. Thus, an accuracy of only ±0.48 mm can be achieved.
Precision definitions for WebChecker
Resolution
Physical resolution: Smallest difference between two edge positions which the sensor clearly distinguishes.
The resolution can be calculated for each edge position. Worst Case = physical resolution.
Resolution is the smallest distinguishable step at the output (or in the display).
according to DIN 1319-2, Fundamentals of Measurement Technology: "Smallest difference of two measured values which the sensor clearly distinguishes."
Example:
Resolution of folding ruler = 1 mm
The MLG-2 WebChecker has a resolution of 0.1 mm. This is the smallest step from one measurement point to the next.
No errors are considered here yet, such as statistical errors or systematic errors.
Repeatability
The repeatability characterizes the spread of the obtained values.
DIN also explicitly points out that a determination procedure works the more precisely, the smaller the "random result deviations" of the procedure are.
A high repetition accuracy (repeatability) has no significance for the overall accuracy.
The MLG-2 WebChecker has a repeatability of 6 µm (1 sigma). This means that the same point, which is measured repeatedly without any further influence, has a scattering of 6 µm.
Total measurement accuracy
Various types of errors are included in the measuring accuracy. Statistical error or systematic error. These can be temperature variations, moving objects, tolerances or different setups. The measurement accuracy already takes all these errors into account. The result for customers can be much more accurate if these errors are minimized.
Differentiation between local and global accuracy?
For local accuracy, only local tolerance errors are considered in the WebChecker.
For global accuracy all tolerance errors over the whole WebChecker are included. Example: If all parts (electronic circuit boards, connectors, ...) have the maximum dimensions (maximum permissible tolerance), then the total width of the web is measured wider.
We have a measuring accuracy of ±0.3 mm with the MLG-2 WebChecker at an optimum measuring position to the object. All systematic and statistical errors are taken into account with 3 sigma.
