Quick Check® SV Series User’s Guide 5 - 7

Bad Reflectance Profile

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. For 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 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.
Bar code signal amplitude
out of range; above yellow
line and also off the graph.
Bar code low
reflectance points not in
straight, consistent
values.