Allen-Bradley GuardPLC 1753, Safety Reference Manual

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30 Publication 1753-RM002C-EN-P - September 2008
Chapter 3 GuardPLC Controller and GuardPLC I/O Module Input Channels
Test Routines
The online test routines perform a walking input test to check
whether the input channels are able, independent of the pending
input signals, to make a through-connection of both signal levels
(L- and H- signal). This functional test is executed with every input
signal reading. The 0 signal (safety state) is processed in the
application program for every error in the input module.
Because the PES has been designed to the closed-circuit current
principle, a 0 signal is processed for the digital inputs in case of error.
See page 14 for an explanation of the closed-circuit current system
principle.
Reaction To Error
If the test routines detect an error in digital inputs, a 0 signal is
processed in the application program for the faulty channel. The
FAULT LED indicator (ERR on the GuardPLC 2000 controller) is
activated.
In addition to the signal value of the channel, the corresponding
channel status signal must be taken into account. When using the
channel status signal in the application program, you have additional
options to configure an error reaction in your program.
Example Block Diagram of Digital Inputs (Using GuardPLC 2000 Controller)
The illustration above does not represent the specifications of the
related module.
42920
T T
I/O Bus
24 channels
Test
ERR RUN
I1 I24