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In the actual circuit, it is necessary to locate the protective device (diode, resistor, capacitor, varistor, etc.) in the immediate vicinity of
the load or contact.
If located too far away, the effectiveness of the protective device may diminish. As a guide, the distance should be within 50cm.
Switching Capacitive Loads
Using relays to switch capacitive loads requires special care. When a switch closes, a transient current flows to charge the capacitance.
This inrush current may be substantially higher than the steady-state current through the system.
Relay's contact welding may occur because of this high inrush current, even though the voltage and steady-state currents are within
the switch specifications.
Any capacitance in the system can contribute to inrush currents, whether it is in a reactive device or from a shielded cable.
Inrush currents can be controlled with series impedance, such as a resistor (about 30 Ω to 50 Ω), between the switch and the
capacitance, as shown in Figure 16.
Precautions for using the long lead wire
If long wires (> 10 m) are to be used in a relay contact circuit, inrush current may become a problem due to the stray capacitance
existing between wires.
Please connect in series the resistance (10 Ω to 50 Ω) in the contact circuit, as shown in Figure 17.
Riferimenti:
National Instruments: http://www.ni.com/white-paper/4197/en/
Panasonic Corporation: General application Guidelines ASCTB250E 201402-T
Hongfa Relay: Explanation of terminology and guidelines of relay
Fujitsu Components: Engineering Reference Relays
Agilent Technologies Inc : Application Note 1399
36
10 Ω to 50 Ω
Figure 12
Lead
Energy storage
(Tens of meters)
capacitance
Figure 13
80618_MAN_IO-LINK IMPACT_12-2019_ENG
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