55
Figure 55 Effect of FIR Length
2.7.6 Getting Optimum Performance from the LCI Sensor
This section describes how to get optimum performance from the LCI sensor.
Proceed as follows:
1.
Position the sample so that the areas requiring the best accuracy are in the middle section of the frame
(middle Z-level).
Note:
The maximum signal level is typically below the middle Z-level. Position surfaces that provide a low signal
below the middle Z-level to improve sensitivity, if possible.
2.
Set FIR Length = 16, Average FIR Length = 2, Peak Threshold = 15.
3.
Set the LED Pulse Width so that Intensity values in the most important area of the profile is between 150 and
240 (meaning the signal is not saturating).
This may cause signal saturation in other areas of the profile. Signal saturation reduces the accuracy of the Z
measurement. Depending on the degree of the saturation, the Z error can be in the range of ±1 µm—±10 µm.
4.
For finding the best compromise, try different combinations of LED Pulse Width, Average FIR Length and Peak
Threshold and FIR Length.
Another way to find the optimum LED pulse width is to use ‘Saturation Limit’-button from the Preview Camera Signal.
This procedure will find the maximum LED pulse giving the most accurate Z-coordinates.
Figure 56 Z-levels for best accuracy and highest signal strength
