Revision 1.9 HC900 Process & Safety Controller Safety Manual 57
01/14
HC900 Control System Fault Detection and Response
Principle of Fault Detection and Response
The goal of fault detection and reaction is to detect and isolate faults that affect the safety of the process
under control, within a time frame that is acceptable for the process Fault detection and reaction occurs at
different levels. These levels are:
•
system level,
•
module level,
•
Channel level.
System level
Combinations of modules and IO faults are controlled at system level. Depending on the hardware and
configuration of a system, the fault reaction to such combinations will be different.
Module level
Faults at module level are controlled at controller level. Depending on the hardware and configuration of a
system, the fault reaction is determined by the Control Processor.
Channel level
Faults at channel level are controlled at controller level. Depending on the hardware and configuration of a
system, the fault reaction is determined by the Control Processor and/or universal module(s).
Diagnostic Test Interval
The Diagnostic Test interval (DTI) is the time in which detection and isolation of faults takes place. The
DTI of the HC900 is a diagnostic suite of test running in the background of the controller. The HC900
diagnostic tests are as follows:
Table 7 – Diagnostic Test Intervals
Sub system Diagnostic Test interval
Micro processor diagnostics 1 Minute
Memory diagnostics 24 hours
Watchdog diagnostics
Once on power cycle of controller (w/o batteries) on startup.
No command required to be sent to do test. Controller does
WD test on start whenever RAM continent is lost (power
cycled w/o batteries).
FPGA diagnostics 800 milliseconds
Flash memory diagnostics Once every restart, new start of controller or scanner
Note: Flash memory is not used during normal operations.
Real Time Clock diagnostics
Once every restart, new start of controller – Note Real Time
Clock is not used during normal operation.
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