Glossary 243
Trident Planning and Installation Guide
fail-safe Characteristic of a device or system to always revert to a safe, predictable state,
even when one or more of its internal elements has failed.
failure System resource perceives that a service resource ceases to deliver the expected
services. The fault-tolerant system masks most failures. See “fault”.
failure rate Rate at which failures occur over time. Usually expressed in failures per million
hours. The inverse of failure rate is MTTF.
fault Cause of a resource failure or an error within the resource.
fault avoidance Result of conservative design techniques using high-reliability components,
system burn-in, and careful design. The goal of fault avoidance is to reduce the
possibility of a failure by designing a device with performance margins so large
that the probability of a detrimental failure is negligible.
fault masking Means of removing failed elements from influencing system operation while
enabling properly operating redundant elements to continue the control process.
fault tolerance Ability to identify and compensate for failed control system elements and allow
repair while continuing an assigned task without process interruption. Fault
tolerance is achieved by incorporating redundancy and fault masking.
FE Functional earth.
FSR Full-scale range. Specifies an operating range for input or output signals. For
example, if 0-5V is the “range,” then 5V is the “full scale”.
host See external host.
hot spare Ability to install spare I⁄O modules with automatic switchover to the spare if the
primary module fails.
input poll time Time required by the controller to collect input data from the controlled process.
Input polling is asynchronous and overlaps application execution.
I/A Series DCS Foxboro Industrial Automation (I/A) Series Distributed Control System.
IEEE Institute of Electrical and Electronics Engineers (IEEE) is a professional society
for engineers.
ISO International Organization for Standardization (ISO) is a world-wide federation of
national standards bodies (ISO member bodies) that promulgates standards
affecting international commerce and communications.
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