16 ProcessLogix and ControlLogix System Redundancy Module
Publication
1757-IN092E-EN-P - November 2007
User-relay Example Application: Connection to an External Switchbox
You can use an external switchbox connected to a user relay on the 1757-SRM
series B module to determine which Logix controller you will attach to the
other RS232 devices on the serial link. You must assemble an external
switchbox to direct serial port devices to one controller of a pair of redundant
Logix controllers. Rockwell Automation does not supply the external
switchbox with the modules.
This example illustrates a connection scheme, with one single-pole
double-throw switch for each RS232 signal. The external power supply output
should not exceed the ratings of the external switchbox coil.
ATTENTION
The line voltage source for the external dc power source to the SRM
Relay Terminals must be the same as that used to power the
energizing SRM Chassis.
Use the same line voltage that provides power to Chassis A, to which
user relay connections are made, to provide input power to the
external power supply. If you use the same line voltage and your
system experiences a line failure to your primary chassis and external
power supply, the external switchbox will switch over to Chassis B.
WARNING
Failure to use an appropriately rated switchbox may result in an
explosion hazard. When installing this equipment in a Class 1,
Division 2 hazardous location, select an external switchbox that is
appropriately certified for use in this environment.
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