understand. Basically, any component inside the laser projector that
requires a ground connection should make a “home-run” to the
“Central Grounding Point”. This connection scheme is called a
“Single-Point Grounding Scheme” which is also known as a “Star
Grounding Scheme”. The “Central Grounding Point” should be
located close to the power supplies.
Unlike the +24V and –24V, which can simply be connected to the
scanner amplifiers in a daisy-chain fashion as shown, the ground
connections (designated PG in the diagram for “Power Ground”)
require more careful consideration, and must each make a “home run”
type connection to the “Central Grounding Point”.
When an AC ground connection is used (green wire on the diagram),
the easiest thing to do would be to connect it to the “Central
Grounding Point” as well. This is because, often times this “Central
Grounding Point” is eventually (through “phantom ground
connections”) connected to the optical plate within the projector. If
“phantom ground connections” can be completely prevented, then the
AC ground connection could simply be connected to the projector
chassis, but not to the central grounding point. This provides the best
performance, but requires the most careful projector design and
layout, and close attention to detail in terms of avoiding “phantom
ground” connections.
When an AC ground is not used, or when the AC ground is connected
only to the projector chassis and there are absolutely no “phantom
ground connections” then ILDA DB-25 pin 25 MUST be connected to
the “Central Grounding Point”.
Note that the ILDA DB-25 pin 25 should NOT be connected to the
“Central Grounding Point” if the AC ground connection is already
connected there, otherwise there will be a ground loop formed
external to the projector, which is undesirable.
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