5.2.6 Recommended items about communication cable installation
Noise generated by many factors such as the type or length of cable, communication speed, and
different communication devices may cause the communication failure with a serial port. It is very
difficult to prevent a communication failure completely. The followings are valid methods to
countermeasure against a noise for the communication cable.
⚫ Use a shield type product for communication cable, and an EMI countermeasure product for the
communication connector hood. Choose the suitable grounding method according to the
operating environment.
[ Both ends grounding (Electromagnetic shielding) ]
The grounding method for reducing the inducted voltage produced in the communication line by
the magnetic field emitted from a power supply line. Shield both ends are grounded by all the
cables of connected communication device. Clamp the STP pump side shield on a connector
hood. A ground loop will be made up through both ends grounding. Connect between GND of a
STP pump and PC with low impedance to prevent ground potential difference.
Figure 37 - Grounding example (Both ends grounding)
[ Single point grounding (Electrostatic shield) ]
This is the grounding method for reducing the electrostatic induction produced in the
communication line by the exogenous noise caused by electrostatic induction or unnecessary
radiation. Ground the communication cable shield by single point to the PC side. DO NOT
ground on STP pump side. When ground potential difference is high, the single point grounding
may be more effective than both ends grounding against a noise.
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