Maximum Line Speed And Exposure Time Calculations - Datalogic Matrix 120 Reference Manual

READING FEATURES

6.4 MAXIMUM LINE SPEED AND EXPOSURE TIME CALCULATIONS

The Exposure Time (or Shutter) parameter defines the time during which the image will be
exposed to the reader sensor to be acquired. This parameter depends heavily on the
environmental conditions (external lighting system, image contrast etc.).
In general, a longer time corresponds to a lighter image but is susceptible to blurring due to
the code movement; a shorter exposure time corresponds to a darker image.
NOTE: The following considerations must be applied only when the internal
lighting system and 2D codes are used. The Maximum line speed allowed for
linear codes or postal code reading applications heavily depends on the
direction of symbol movement. When the direction of movement is parallel to
the elements of the code, the maximum speed is greater.
Assuming:
 X: Code Resolution (mm)
 T
: Exposure Time (s)
exp
 LS: Line Speed (mm/s)
The essential condition to avoid blurring effects between two adjacent elements in a dynamic
reading application is:
The maximum (theoretical) line speed LS can be calculated as follows:
T is the minimum Exposure Time value obtainable for the specific application. It can
exp (min)
be evaluated in static reading conditions and depends on the Matrix reader model selected
for the application (internal lighting system, optical lens, reading distance) and on any
external lighting system. It may also depend on code printing quality, and reader position.
Example:
A Matrix 120 using:
Internal Lighting Mode = Very High Power Strobe
Exposure Time (
Code Resolution (X) = 0.254 mm (10 mils)
has a maximum line speed of:
LS  T
X / T
exp (min)
 
s) = 200 s
0.254 (mm) / 0.0002 (s) = 1270 mm/s
 X
exp
= LS
(max)
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