Environmental Engineering Reference
In-Depth Information
which an electromagnetic environment
is classiied, are presented in NP, 2000;
Rozen, 2007; Rozen, 2008).
• When selecting a degree of test hardness,
those (and only those) features of elec-
tromagnetic environment, which can be a
cause of occurrence and have a signiicant
inluence on intensity of disturbances of
that type, towards which tests are executed,
are considered.
• Adequate supplies of calculating and other
resources (inputs, outputs, memory, power
supply, etc.)
• Redundancy of components of I&C sys-
tems and component parts of SHC, per-
forming category A and B, and equipment
and connecting lines, which are used for
transmission of signals and messages be-
tween them and reception of required in-
formation from other systems.
• Availability of devices that can detect devi-
ations from a determined behavior and au-
tomatically recover normal operation (for
example, timer, executing restart in case of
program circularity or temporary loss of
input data).
• Availability of technical diagnostic facili-
ties, which provide continuous checking of
a technical state and allоw promptly detect-
ing operation failures of component parts,
which can lead to a failure during initiation
of a discrete function.
• A possibility of algorithm restructur-
ing, which allows recovering operation of
failed elements in a normal mode or trans-
ferring to a preliminary provided standby
mode, for example, in case of unreliability
of received data or a loss of input data that
is impossible to eliminate.
Standards and rules of noise immunity estima-
tion, test methods and criteria of result estimation
meet international standards IEC 2001a - IEC
2001g; IEC, 2002a - IEC, 2002c; IEC 2005b; IEC,
2006a and identical with them State standards of
Ukraine (Rozen, 2007, Rozen, 2008).
Resistance to Failures of Elements
Safety important I&C systems and SHC are de-
signed (developed) in such a way that they could
continue operation with preliminary determined
behavior in case of single failures of their elements
and / or element failures in adjacent I&C systems
and in channels, through which information is ob-
tained from these systems. Each of main functions
of the I&C system and SHC is performed and meet
specified requirements in case of failure of any
elements of the same system (SHC), participating
in functions execution of lower category.
Failures of elements in primary and secondary
power supply systems do not influence functions
of the I&C system (SHC). If such failures lead to
short-term power break, not exceeding a specified
time period, they do not influence performance
of category A and B functions; performance of
category C functions is continued in a previous
mode after power supply recovery.
Resistant to failures of elements is provided
in I&C systems and SHC of 2(А) and 3(В) safety
classes:
For assurance of resistance to failures of in-
formation sources or connecting lines:
• Validity of input analog signals (for exam-
ple, when this signal is staging in working
range what have deined preliminary for
designate parameter) is checked and unre-
liable data are automatically eliminated.
•
For formation, transmission and input of
data about the state of a controlled object,
two-beat signals are used instead of one-bit
binary signals, when logical levels 01 and
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