3-2Series 90-30/20/Micro Programmable Controllers Reference Manual – September 1998 GFK-0467K
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Section 1: Fault Handling Note
This information on fault handling applies to systems programmed using
Logicmaster 90-30/20/Micro software.
Faults occur in the Series 90-30 , 90-20, or Series 90 Micro PLC system when certain failures or
conditions happen which affect the operation and performance of the system. These conditions,
such as the loss of an I/O module or rack, may affect the ability of the PLC to control a machine or
process. These conditions may also have beneficial effects, such as when a new module comes
online and is now available for use. Or, these conditions may only act as an alert, such as a low
battery signal which indicates that the battery protecting the memory needs to be changed.
Alarm Processor The condition or failure itself is called a fault. When a fault is received and processed by the CPU,
it is called an alarm. The software in the CPU which handles these conditions is called the Alarm
Processor. The interface to the user for the Alarm Processor is through the programming software.
Any detected fault is recorded in a fault table and displayed on either the PLC fault table screen or
the I/O fault table screen, as applicable.
Classes of Faults The Series 90-30, 90-20, and Micro PLCs detect several classes of faults. These include internal
failures, external failures, and operational failures.
Fault Class Examples
Internal Failures Non-responding modules.
Low battery condition.
Memory checksum errors.
External I/O Failures Loss of rack or module.
Addition of rack or module.
Operational Failures Communication failures.
Configuration failures.
Password access failures.