Environmental Engineering Reference
In-Depth Information
remained failures, time period of its occurrence
and elimination is shown in the screen.
Facilities of human-machine interface on
workplaces of personnel, that controls a state and
provides maintenance and recovery of the I&C
system, are manufactured, labeled and placed in
such a way that it would be possible to accurately
assess a state of the system and its components,
detect places of occurrence and a nature of op-
erability failures and make a solution for their
elimination.
SHC in separate cases or supporting constructions
inside one case). Preferable ways of physical sepa-
ration of cables are the use of individual cables
of channels and penetrations.
Independence from Deactivation or Oper-
ability Violations:
Of individual components
of the I&C system, SHC or redundant channels
is provided due to a functional and / or electric
separation. Functional separation (“functional
isolation”) is provided by the fact that each I&C
system (SHC, redundant channel) has a full set of
input data required for performance of specified
functions, electric separation - galvanic isolation
and circuit shielding (electric separation is pro-
vided in cases, when for different I&C systems,
SHC and / or redundant channels a common source
of input data, a common signal receiver and / or
one and the same power source are used).
For galvanic isolation electric, optic and other
separation devices (“isolators”), fiber optic lines
and local networks, transmitting information in the
form of optic signals, are used. Quality of galvanic
separation is defined by electric strength of isola-
tion between galvanic isolated or isolating during
the operation by electric circuits and between the
enclosure and all isolated from the enclosure elec-
tric circuits of device and by resistance of electric
isolation between the same circuits.
Electric strength of isolation is defined by the
value of test voltage of a direct current or an am-
plitude value of the test voltage of an alternating
current, being applied during one minute between
a tested circuit and interconnected clips of other
circuits, including safety-ground clips that do not
cause breakdown or isolation breaking. Value of
test voltage, depending on a device safety class,
circuit nominal voltage and conditions for execu-
tion of tests, should be not lower than the specified
ones in Table 16.
Electric isolation resistance between the
tested circuit and interconnected clips of other
circuits, including ground clips:
INDEPENDENCE OF FUNCTIONS
Property of Independence
A group of mutually redundant I&C systems or
SHC of 2(А) safety class remains operable and
keeps specified properties during performance of
category A functions independently from possible
(considered by the project) external influencing
factors and / or in case of deactivation, operability
failure of one of these systems or SHC, and as a
result of faulty actions of the personnel during their
maintenance or recovery. A group of redundant
channels of one I&C system or SHC of 2(А) safety
class has similar properties. Each I&C system
(SHC) of 2(А) safety class remains operable and
keeps specified properties during performance of
category A functions independently from the state
of any element, a group of elements or a channel
of the same system, intended for performance of
lower category functions, or any adjacent I&C
system (SHC) of lower safety class.
Independence from External Influencing Fac-
tors:
(Such as fire, flood, extreme temperature
and humidity, electromagnetic disturbances, etc.)
and from faulty actions of personnel that provides
maintenance or recovery, is provided by physi-
cal separation of components of different I&C
systems, SHC and their redundant channels, and
related cables (for examples, location of SHC in
different rooms, using redundant channels of one
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