3. Cabling
3-109
TI 33Q01J10-01E
Feb. 1, 2009-00
Use of Relays
Contact protection and surge absorption can be provided in various manners. When using
contacts output to drive relays and solenoids, the following precautions should be taken:
• Install a diode in parallel to induction load for noise prevention and contact protection.
• Use a relay circuit with voltage rating as low as possible for increased reliability.
• Select a diode having a reverse withstand voltage which is 10 times or larger than a circuit
voltage and a forward current which exceeds a load current.
IMPORTANT
Relays and solenoids cause reverse electromotive voltages at both coil ends due to inductive
load. This phenomenon causes contact damage or noise, leading to device errors and adversely
affecting the entire system.
When a DC Power Supply Is Used
F031002.ai
Contact
Power
supply
Inductive load such as
electromagnetic valve
External circuit
System side
Figure Example of Using Diode for Contact Protection
When a AC (or DC) Power Supply Is Used
• Shunt the load with a resistor (R) and a capacitor (C).
• The recovery time increases when using relays or solenoid valves.
Inductive
load
F031003.ai
Note: Avoid direct AC voltage input to the contact output terminal on 19-inch rack mountable type.
Figure Example of Capacitor/Resistor-protected Circuit
