Skew Angle - Ametek LAND LSP HD Series User Manual

LSP Linescanner Head
HD

6.5 Skew Angle

When a linescanning thermometer is scanning across a moving product travelling along
a line, setting the scan frequency too low may cause the scan line to be excessively
tilted, or 'skewed'. When the product speed is high and the scan frequency is low, the
skew is more apparent, and results in an inaccurate indication of product width.
Product movement
The scan skew angle is given by:
e.g. At a scan frequency of 50Hz, a target distance (D) of 2m and product speed of 10m/s ......... θ = 0.91°
Apparent (measured) product width = actual product width
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Skew angle
θ
θ
θ
product speed

θ
 TAN − 1

 
2 π d scan frequency

Example 1 - A greater skew angle
is created when high product
speeds are combined with low scan
frequencies.
Note: During product width
calculations, the apparent width is
displayed greater than the actual
width.
Example 2 - When high product
speeds are combined with medium
scan frequencies, the skew angle is
reduced when compared to Example 1.
Example 3 - When high product
speeds are combined with high
scan frequencies, the skew angle
is negligible when compared to
Example 1.
product


 TAN − 1
 
scan speed
 
(ignoring edge correction errors)
Cos θ
User Guide
speed


