Rockwell Automation DeviceNet Media Design Installation Guide - Manual (Page 118)

Publication DNET-UM072C-EN-P - July 2004
B-2 Power Output Devices
Noise or Transient
Protection The typical actuators used in DeviceNet control systems utilize inductive coils
that generate transients when de-energized. You must use appropriate
protection to suppress transients during coil de-energization. Add a diode
across the inductive coil to suppress transients on the actuator’s dc coils. Use a
MOV varistor module suppressor for a 24V dc coil if this added drop out time
with the diode is unacceptable. This varistor module must clamp the transient
voltage across the coil at 55 volts to prevent the output contact from arcing on
switch separation.
Typical actuators used in DeviceNet control systems use inductive coils and
limit current transients on energization by their inherent L/R time constant.
Any transients due to contact bounce on energization will be suppressed by
the transient protection utilized for coil de-energization.
ATTENTION
Do not use DeviceNet power on dc coil actuators that use
economizing coils to operate. They have high inrush
currents.