PSS 21H-1B2 B3
Page 2
Enhanced Reliability
The Control Processor 30 offers optional fault-
tolerance for enhanced reliability. The fault-tolerant
control processor configuration consists of two
parallel-operating modules with two separate
connections to the Nodebus and to the Fieldbus.
The two control processor modules, married together
as a fault-tolerant pair, are designed to provide
continued operation of the unit in the event of virtually
any hardware failure occurring within one module of
the pair. Both modules receive and process
information simultaneously, and faults are detected by
the modules themselves. One of the significant
methods of fault detection is comparison of
communication messages at the module external
interfaces. Upon detection of a fault, self-diagnostics
are run by both modules to determine which module
is defective. The non-defective module then assumes
control without affecting normal system operations.
To further ensure reliable communications, the fault-
tolerant control processor performs error detection
and address verification tests in its Nodebus and
Fieldbus interfaces.
For enhanced reliability during maintenance
operations, the Control Processor 30 is equipped with
a recessed reset button, located at the front of the
module. This feature provides for manually forcing a
module power off and on (reboot) without removing
the module from the enclosure.
Diagnostics
The Control Processor 30 uses three types of
diagnostic tests to detect and/or isolate faults:
• Power-up self-checks
• Run-time and watchdog timer checks
• Off-line diagnostics
Power-up self-checks are self-initiated when power is
applied to the control processor. These checks
perform sequential tests on the various control
processor functional elements. Red and green
indicators at the front of the control processor module
reflect the successful (or non-successful) completion
of the various phases of the control processor startup
sequence.
The run-time and watchdog timer checks provide
continuous monitoring of control processor functions
during normal system operations. The operator is
informed of a malfunction by means of printed or
displayed system messages.
Off-line diagnostics are temporarily loaded into the
system for the purpose of performing comprehensive
tests and checks on various system stations and
devices. Using the off-line diagnostics, a suspected
fault in the control processor can be isolated and/or
confirmed.
Fieldbus Modules
Fieldbus Modules provide connection of digital I/O,
analog I/O, and Intelligent Transmitters to control
processors. There are two types of Fieldbus Modules:
main and expansion. Some main modules can be
expanded using expansion modules.
A wide range of Fieldbus Modules is available to
perform the signal conversion necessary to interface
the control processor with field sensors and
actuators. For further information on the Fieldbus
Modules, refer to the Fieldbus Modules Product
Specification Sheet (PSS).
Fieldbus Flexibility
The Control Processor 30 is used in three different
Fieldbus configurations, which provide broad flexibility
in Fieldbus implementation:
• Local Fieldbus (Figure 1) - Used only within the
enclosure, the local bus can extend up to 10 m
(30 ft). Up to 24 Fieldbus Modules (excluding
expansion modules) attach directly to the local
bus, which is redundant.
Figure 1. Local Fieldbus (Typical Configuration)
CONTROL
PROCESSOR 30*
REDUNDANT FIELDBUS
TO/FROM PROCESS DEVICES
*OPTIONALLY FAULT-TOLERANT
FIELDBUS
MODULE
FIELDBUS
MODULE
FIELDBUS
MODULE
FIELDBUS
EXPANSION
MODULE
ENCLOSURE
(7 pages)
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