Nordic ID RF651 User Manual page 36

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APPENDIX B - Introduction to the Laser Engine
A laser diode produces a single beam of coherent light which deflects off a mirror, and is emitted from the laser engine
used inside the RF651. The total deflection of the single beam is 53° (standard version), and the scan frequency is 39
scans per second.
When the laser beam strikes a barcode, the dark bars absorb most of the light while the light spaces reflect most of it.
Thus, changes in the reflected light can be used to deduce the barcode into electronic format. A photo diode is used to
sense the reflected laser light and generate a current proportional to the reflected light signal. The current then produces
an analogue voltage, which is further amplified, filtered to minimise noise related problems and then finally sent to a
digitiser, which transforms the analogue signal into digital form representing the barcode. This is called the Digitised Bar
Pattern (DBP).
The DBP data is then sent to the decoder board for processing into a host-compatible format and further applications
are based on the software used.
The technical specifications of the laser engine used in the RF651 are listed in the table below.
Item
Laser Power (at 650 nm)
Optical Resolution
Print Contrast
Scan Angle
Environmental characteristics
Ambient light immunity:
Scan rate
Scanning angles
Reading distances
Table: Laser engine technical specifications
© 2006 Nordic ID oy
RF651 User Manual
Description
Scan mode; 1.7 mW (± 0.2 mW)
Aim mode: 0.5 mW (± 0.05 mW)
CDRH Class II/IEC Class 2
0.004 in. minimum element width
Minimum 25% absolute dark/light reflectance measured at 650
nm.
Wide: 47° ± 3°
Narrow: 35° ± 3°
Sunlight:
Artificial Light 4,844 lux (450 ft. candles)
92 minimum., 104 typical, 116 max. scans/sec (bidirectional)
scan angle: 47° ± 3° (wide), 35° ± 3° (narrow)
skew: 100% UPC at 5 in. ± 50° from normal
pitch: 100% UPC at 5 in. ± 65° from normal
tilt: 100% UPC at 5 in. ± 35° from vertical
Near ranges on lower densities (not specified) are largely
dependent upon the width of the bar code and the scan angle.
Version 1 June 2006
107,640 lux (10,000 ft. candles)
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