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DATALOGIC
DP1100
Grounding Rules
Shielding the communication cable is an effective way to protect against
capacitive conduction and radiated interference, while the effect against
noise due to inductive coupling is small. In any case, the shielding effect
occurs only if the shield is grounded; otherwise the entire voltage of the
shielded material will be floating and will not give protection against electrical
noise.
When installing the DP1100 in a large system, remember that a voltage drop
may occur between ground connections made at distant points. This could
be the undesirable effect of variable electromagnetic fields due, for instance,
to the presence of engines, leakage currents, lightning or other sources. For
long distances between the devices (about 50 meters, but this length
depends widely on the environment), the voltage drop between ground
connections can be 100 V or higher.
If you ground the shield in several points the voltage drop across the shield
will cause a current, increasing the noise on the signal wires.
Therefore, to avoid damage to the device drivers and loss of system
performance in general, the shield should be grounded at most in one point
only.
Since the shielding protection is more effective near to the ground
connection, it is advisable to ground the shield where electric noise is higher.
Typically this is done at the DP1100 device. The shield is provided on J1 Pin 1.
Bad shielding
effect
Good shielding
effect
Figure 2.11 - Shield grounding effect
Installation - 2.11
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