IAI America ERC2 - Manual (Page 34)

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1. Overview
11
(2) Noise sources and elimination
Among the numerous noise sources, solenoid valves, magnet switches and relays are of particular concern
when building a system. Noise from these sources can be eliminated by implementing the measures specified
below.
[1] AC solenoid valves, magnet switches and relays
Measure: Install a surge absorber in parallel with the coil.
[2] DC solenoid valves, magnet switches and relays
Measure: Install a diode in parallel with the coil. Determine the diode capacity in accordance with the load capacity.
In a DC circuit, connecting a diode in reverse polarity will damage the diode,
internal parts of the controller and/or DC power supply, so exercise due
caution.
m Point
Install a surge absorber to each coil over a minimum wiring length.
Installing a surge absorber to the terminal block or other part will be
less effective because of a longer distance from the coil.
Surge absorber
Diode