KEYENCE Visual KV Series - Manual (Page 93)

Chapter 2 System Installation 1-69
1
2
Visual KV
Series
2.1 Installation Environment
Cautions on grounding
Because the Visual KV Series is constructed to be sufficiently resistant to noise, it
can usually be used without being grounded. However, when the Visual KV Series is
used in an environment with a lot of noise, grounding is required. In such a case,
pay strict attention to the following contents.
• Perform complete grounding for each individual unit. In this case, the ground
resistance should be 100 Ω or less.
• If individual grounding is not possible, perform common grounding. In this case,
the length of each grounding cable should be equal.
2.1.5 Contact Protection
If inductive loads such as clutches, motors, and solenoids are used, a rush current
may flow when the load power supply is turned on, or a counter electromotive
voltage may be generated when the load power supply is shut down. The rush
current and the counter electromotive voltage can contribute considerably to
shortening the service life of the contacts. To prevent this from happening, provide a
contact protection circuit.
■ Contact protection circuit examples
When the supply voltage is 24 to 48 V, provide a protection circuit in position "b".
When the supply voltage is 100 to 200 V, provide a protection circuit in position "a".
Note 1: Use a load coil whose rating is less than the contact capacity.
Note 2: Use a diode whose peak inverse voltage is 10 times or more the circuit
voltage and whose forward current is not less than the load current.
Note 3: Individually attach diodes, varistors, and CR circuits directly to the relay coil
terminal.
KV Other device Other device Other device KV
A = B A > B
A < B
B
B
A
KV
A
Complete grounding
Recommended Acceptable Unacceptable
a b
For AC load 1
Contact
Load CR circuit
For DC load 1
Contact
Load Diode
For AC load 2
Contact
Varistor
For DC load 2
Contact
Zener diode
KVHKA Chap 02.p65 08.3.11, 11:11 AM 69