5-10
5.2.2 Grounding
In situations of excess noise
Under normal conditions, the inherent noise resistance is sufficient. However, in situations of excess
noise, ground the instrument to increase noise suppression.
Exclusive grounding
• The grounding connection should have a resistance of less than 100Ω.
• The point of grounding should be as close to the PLC unit as possible. The ground wire should be as
short as possible.
• If two devices share a single ground point, it may produce an adverse effect. Always use an exclusive
ground for each device.
Note:
Depending on the surroundings in which the equipment is used, grounding may cause problems.
[Example]
Since the power supply line of the FPΣ power supply connector is connected to the function earth
through a varistor, if there is an irregular potential between the power supply line and earth, the varistor
may be shorted.
Do not ground the FPΣ function earth terminal when grounding a plus (+) terminal of the power.
In some computers, the SG terminal of RS232C port and connector shieldingare connected. Also the
FPΣ tool port shielding is connected with the function earth terminal. Therefore, the GND terminal of FPΣ
and the function earth terminal are connected if the computer is connected. Especially when the FPΣ is
connected to a computer with a plus (+) terminal grounded, therefore, an FPΣ’s minus (-) terminal is
connected with the function earth terminal. As a result, short circuit occurs which may lead to the
breakage of FPΣ and its neighboring parts.
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