254764-001 Rev B 17
Bar Code Travel Direction
Bar codes can be scanned in a static location, or more commonly with on-line scanner/verifiers, they can be
scanned while moving through the laser beam. Refer to Figure 3. It shows the two directions a bar code can
travel through the laser beam. They are designated “picket fence” and “ladder” directions.
Figure 3 – Scan Direction
Picket Fence Travel Direction
Laser Beam
Ladder Travel Direction
The SV unit must be programmed for the direction of travel of the codes being analyzed. If the codes
are being scanned in a static condition, use picket fence travel direction.
Bar Code Travel Speed Considerations
A bar code should be present in the beam for at least five scans for most reliable operation. The SV 2 Series
performs a minimum of 100 scans/analyses per second. At that rate, each analysis is accomplished in 10
milliseconds max. Therefore, a bar code must be in the beam for at least 50 milliseconds to be reliably
analyzed. Some SV models have higher minimum scans/analysis, therefore a bar code must be in the beam
for less amount of time for those models.
Picket Fence Direction
In picket fence travel direction, a bar code is in the laser beam throughout the height of the shortest bar in
the code. An easy way to estimate the fastest speed the code can travel through the beam is to divide the
height of the shortest bar in the code by the maximum time required for the SV unit to take five scans of the
code. Example: Calculate the maximum travel speed where the shortest bar height in a code is .5 inches and
the SV model being used performs a minimum of 100 scans/analyses per second. Five scans requires 50
milliseconds (.05 seconds) to gather, so .5 inches (bar code height) divided by .05 seconds (time needed to
gather 5 scans) = 10 inches/second. Therefore the maximum speed the code can travel through the beam is
10 inches per second.
Vertical distance between bar codes is also a speed consideration in picket fence direction. The SV 2 Series
must have five continuous scans where no bar code is detected to reliably exit a bar code when operating in
the standard operation mode set by Command ~HO1. Assuming 100 scans per second minimum, this
means the vertical distance between the codes must take at least 50 milliseconds to pass through the laser
beam. Calculate the maximum speed by measuring the shortest vertical space between bar codes on a label
(or between labels.) Divide this distance by .050 (seconds). The result is the fastest speed the codes can
move through the beam. If the application travel speed cannot be met due to a short vertical distance
between codes, Command ~HO2 can be used to cause the SV to exit on a change in data rather than
detecting no bar code.
If using ~HO2, ensure the bar codes with short vertical gap are encoded with
different data and only one code across is being analyzed in each scan.
The slower of the two print speeds calculated above for bar height and gap height is the maximum
recommended speed for picket fence travel.