ZBA ZB-3062, Руководство пользователя

Страница: 26 / 89

ZBA Inc.
26
7.4 Thermal and Centering
Thermal Considerations
Care must be taken when designing the Image Engine into any system. Internal heating of the Image Engine can occur in high duty cycle scanning
applications in several ways. The high visibility aimer dissipates a significant amount of power as heat. The illumination and aiming LEDs also release heat,
and are a major contributor to thermal increases in high use or in presentation mode. An increase in temperature around an Image Engine can cause noise
levels on the imager, degrading image quality. The thermal rise can also affect the laser diode. In a continuous scanning or high use environment, the Image
Engine temperature can rise 15° to 20°C. Under high ambient temperature conditions, the laser diode is at risk of thermal breakdown and possible failure.
The image quality and decode performance will also degrade. The Power Control PWM can be used to reduce the effect of the Illumination LEDs on thermal
rise, however, this also reduces the intensity of the illumination. Reducing the intensity of the illumination reduces total power used but can also reduce the
depth of field in low light environments.
Centering
Use Centering to narrow the imager’s field of view to make sure the imager reads only those bar codes intended by the user. For instance, if multiple codes
are placed closely together, centering will insure that only the desired codes are read. (Centering can be used in conjunction with Aimer Delay , for the most
error-free operation in applications where multiple codes are spaced closely together. Using the Aimer Delay and Centering features, the imager can emulate
the operation of older systems, such as linear laser bar code imagers. In the example below, the gray area is the full imager field of view and the white area is
the centering window. Bar Code 1 will not be read, while Bar Code 2 will be.
The default centering window is a 128x96 pixel area (640x480 default image size) in the center of the imager’s field of view. The following diagram
illustrates the default top, bottom, left, and right pixel positions, measured from the top and the left side of the imager’s field of view.