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HAPTER
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I
NTRODUCTION
ALR-9900
H
ARDWARE
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ETUP
G
UIDE
DOC.
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#8102086-000
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Mechanical: Reader Physical Size
Figure 1 - Outline Drawing of the ALR-9900
I/O Port Terminal Interface
The ALR-9900 I/O port provides four digital inputs and eight digital outputs,
optically isolated from the reader circuitry. Opto-isolators have two basic
elements: a light source (usually a light emitting diode) and a photo-sensitive
detector. These two elements are positioned facing one another and inserted in
an electrical circuit to form an opto-coupler. The key property of an opto-coupler
is that there is an insulating gap between the light source and the detector. No
current passes through this gap, only the desired light waves representing data.
Thus the two sides of the circuit are electrically isolated from one another.
This protects the circuitry inside the reader from damaging ground loops (when
the external device is at a different ground potential than the reader), and voltage
spikes.
