5-105.2.2 GroundingIn situations of excess noiseUnder normal conditions, the inherent noise resistance is sufficient. However, in situations of excessnoise, 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 asshort as possible.• If two devices share a single ground point, it may produce an adverse effect. Always use an exclusiveground 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 earththrough a varistor, if there is an irregular potential between the power supply line and earth, the varistormay 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 theFPΣ tool port shielding is connected with the function earth terminal. Therefore, the GND terminal of FPΣand the function earth terminal are connected if the computer is connected. Especially when the FPΣ isconnected to a computer with a plus (+) terminal grounded, therefore, an FPΣ’s minus (-) terminal isconnected with the function earth terminal. As a result, short circuit occurs which may lead to thebreakage of FPΣ and its neighboring parts.
