User manual

Publication 1747-UM011F-EN-P - May 2007
Selecting Your Hardware Components 53
Suitable surge suppression methods for inductive ac load devices
include a varistor, an RC network, or an Allen-Bradley surge
suppressor. These components must be appropriately rated to
suppress the switching transient characteristic of the particular
inductive device.
For inductive dc load devices, a diode is suitable. A diode, catalog
number 1N4004, is acceptable for most applications.
A surge suppressor can also be used. See the table on page 51.
Locate the suppression device as close as possible to the load device.
Transistor Output Transient Pulses
This section applies to the following SLC 500 fixed I/O processors and
SLC 500 I/O modules that have transistor outputs.
For the SLC 500 products listed above, the maximum duration of the
transient pulse occurs when minimum load is connected to the
output. However, for most applications the energy of the transient
pulse is not sufficient to energize the load.
Fixed I/O processors with
transistor outputs
I/O modules with transistor outputs
• 1747-L20E
• 1747-L20G
• 1747-L20L
• 1747-L20N
• 1747-L30L
• 1747-L40E
• 1747-L40L
• 1746-OB8
• 1746-OBP8
• 1746-OV8
• 1746-OB16
• 1746-OB16E
• 1746-OB16EI
• 1746-OBP16
• 1746-OV16
• 1746-OVP16
• 1746-OB32
• 1746-OB32E
• 1746-OV32
ATTENTION
A transient pulse occurs in transistor outputs when the external
dc supply voltage is applied to the common output terminals (for
example, via the master control relay). The sudden application of
voltage creates this transient pulse. (See the following graph.)
This condition is inherent in transistor outputs and is common to
solid state devices. A transient pulse can occur regardless of the
processor having power or not.