Correcting Malfunctions Due To Noise - Omron DEVICENET Operation Manual

Minimizing Noise in the Network
Considerations when
Using Flat Cable
2-5-2

Correcting Malfunctions due to Noise

Problems with the
Communications
Cable Shielding
Problems with the
Communications
Power Supply
84
To prevent unstable operation due to interference when using flat cable in mul-
tiple DeviceNet systems, keep each flat cable at least 5 mm apart from any
other flat cable.
When noise is thought to be the cause of a malfunction in the DeviceNet net-
work, the following countermeasures may be effective.
Isolate the communications cable shielding wire by disconnecting it from the
ground.
Disconnecting the ground will reduce the noise transferred from the ground to
the communications cable. This countermeasure also reduces the noise cur-
rent that flows in the shield wire.
Isolate the communications power supply.
This countermeasure reduces the noise transferred from the communications
power supply ground to the communications cable and the noise current that
flows in the communications cable. A switching power supply is usually con-
nected to the case with capacitors as shown below, so the power supply itself
must be insulated from the control board as well as being disconnected from
the FG terminal.
Typical Switching Power Supply Construction
AC input
AC power supply
Typical switching power supply construction
Isolating the Communications Power Supply
Example 1:
Isolating an S82J Power Supply
S82J Power Supply
S82Y-@@N (Mounting Tool)
Switching power supply
Power
DC output
supply
circuit
Case
Example 2:
Isolating another Power Supply
DC power supply
Insulator such as
plastic or acrylic
Section 2-5