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
exp
: Exposure Time (s)
• LS: Line Speed (mm/s)
Conversion to Metric
• [Code Resolution in mils] x 0.0254 = Code Resolution in mm
• n/a
• [Line Speed in ft/min] x 5.08 = Line Speed in mm/s
The essential condition to avoid blurring effects between two adjacent elements in a dynamic reading application is:
LS × T
exp
≤ X
The maximum (theoretical) line speed LS can be calculated as follows:
X / T
exp (min)
= LS
(max)
T
exp (min)
is the minimum Exposure Time value obtainable for the specific application. It can be evaluated in static reading
conditions and depends on the ABR 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.
Examples
ABR 7000 using:
Internal Lighting Mode = Very High Power Strobe
Exposure Time (µs) = 100 µs
Code Resolution (X) = 0.254 mm (10 mils)
has a maximum line speed of: 0.254 (mm) / 0.0001 (s) = 2540 mm/s
Likewise, T
exp (max)
is the maximum Exposure Time value that can be used without blurring for the given application line
speed and code resolution. Therefore: X / LS = T
exp (max)
T
exp (max)
and LS
(max)
are represented in the graph below as the curved line for X (code resolution). Values above the curve
result in blurring. In practice, the application values are somewhere below the theoretical line, (in the dark gray area), due to
environmental and other conditions.
SW Limit
Line Speed
Readable
Blurring
SW/HW Limit
T
exp
T
exp (min)
Conveyor Speed
Limit
X
2X
Figure 147. Maximum Line Speed and Exposure
For example, the maximum target speed in the application is also affected by these conditions:
• Code/Background Contrast: Maximum speed decreases when decreasing image contrast (poor quality codes,
reflective transparent coverings, different supports and printing techniques)
• Code Resolution: Maximum speed increases when decreasing code resolution, (that is, 2X). There is a decrement of
overlapping effects between two adjacent elements
• Tilt Angle: Maximum speed decreases when increasing Tilt angle (from 0 to 45 degrees)
The Internal Lighting parameter allows setting the operating mode of the internal lighting system. The possible values are:
ABR 7000 Series Barcode Reader
118
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