HandHeld SV series, User Manual

Page: 41 / 104

Quick Check® SV Series User’s Guide 5 - 3
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.
Note: 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.
Note: The slower of the two print speeds calculated above for bar height and
gap height is the maximum recommended speed for picket fence travel.
Picket Fence Bar Code Positioning Specifications:
• Four codes across maximum
• Horizontal gap between codes: .5 inch (13 mm) minimum
• Maximum number of codes per sync period: 99
Ladder Direction
In ladder direction, one bar code at a time is usually in the beam. The amount of
time the code is in the beam is a function of the total width of the code (including
quiet zone), the length of the beam area that is used for scanning and the speed
the code is travelling. The distance the bar code is in the beam is calculated by
subtracting the bar code width from the length of the beam programmed to scan
the bar code. (
See "Setting Ladder Mode Scanning Length Using ScanView
Software" on page 5-4 .) Divide this difference by the amount of time the SV
model requires to gather 5 scans to get the maximum speed. For example, a bar