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GFK-0467K Chapter 3 Fault Explanation and Correction 3-3
3
Note
For information specific to Micro PLC fault handling, refer to chapter 7 of the
Series 90 Micro PLC User’s Manual (GFK-1065).
System Reaction to Faults
Typically, hardware failures require that either the system be shut down or the failure is tolerated.
I/O failures may be tolerated by the PLC system, but they may be intolerable by the application or
the process being controlled. Operational failures are normally tolerated. Series 90-30, 90-20, and
Micro PLC faults have two attributes:
Attribute Description
Fault Table Affected I/O Fault Table
PLC Fault Table
Fault Action Fatal
Diagnostic
Informational
Fault Tables
Two fault tables are maintained in the PLC for logging faults, the I/O fault table for logging faults
related to the I/O system and the PLC fault table for logging all other faults. The following table
lists the fault groups, their fault actions, the fault tables affected, and the “name” for system discrete
%S points that are affected.
Table 3-1. Fault Summary
Fault Group Fault Action
Fault
Table Special Discrete Fault References
Loss of or Missing I/O Module Diagnostic I/O io_flt any_flt io_pres los_iom
Loss of or Missing Option Module Diagnostic PLC sy_flt any_flt sy_pres los_sio
System Configuration Mismatch Fatal PLC sy_flt any_flt sy_pres cfg_mm
PLC CPU Hardware Failure Fatal PLC sy_flt any_flt sy_pres hrd_cpu
Program Checksum Failure Fatal PLC sy_flt any_flt sy_pres pb_sum
Low Battery Diagnostic PLC sy_flt any_flt sy_pres low_bat
PLC Fault Table Full Diagnostic — sy_full
I/O Fault Table Full Diagnostic — io_full
Application Fault Diagnostic PLC sy_flt any_flt sy_pres apl_flt
No User Program Informational PLC sy_flt any_flt sy_pres no_prog
Corrupted User RAM Fatal PLC sy_flt any_flt sy_pres bad_ram
Password Access Failure Diagnostic PLC sy_flt any_flt sy_pres bad_pwd
PLC Software Failure Fatal PLC sy_flt any_flt sy_pres sft_cpu
PLC Store Failure Fatal PLC sy_flt any_flt sy_pres stor_er
Constant Sweep Time Exceeded Diagnostic PLC sy_flt any_flt sy_pres ov_swp
Unknown PLC Fault Fatal PLC sy_flt any_flt sy_pres
Unknown I/O Fault Fatal I/O io_flt any_flt io_pres