Environmental Engineering Reference
In-Depth Information
10 are interpreted as two diferent states
of an object (for example, connected and
disconnected), at this time logical levels 00
and 11 indicate an error of a signal source
or a damage of a connecting line.
• Main safety important technological pa-
rameters are preferably monitored by a
direct measuring method rather than cal-
culated on the basis of measured values of
other parameters (indirect measurements).
• When choosing a measurement range for
each monitored parameter, a possibility of
exceeding a range of working values of this
parameter in emergencies and accidents is
considered.
• If for a satisfactory coverage of all range
of a monitored parameter more than one
sensor is required, a proper overlapping
of adjacent measurement ranges and auto-
matic switching of these sensors are pro-
vided in order that saturation or corruption
inluence on range boundaries does not
prevent reception of results with a required
accuracy.
• In case of inoperability or removal from
operation of one of a redundant measuring
channel (control or alarm channel), other
channels should meet speciied accuracy
requirements.
• Measuring channels, control and alarm
channels, in which redundancy of compo-
nent parts is provided, should meet speci-
ied accuracy requirements in case of fail-
ure of any of these component parts.
•
For reception of commands of remote con-
trol from operational personnel keys with
three states, connected with a three- or
four-wired scheme in such a way that any
command is generated during a simultane-
ous opening of a control circuit (closed at a
mid position of the key) and closed control
circuits in one of two extreme positions of
the key, are used.
For assurance of resistance to failures of ele-
ments in channels of digital message transmis-
sion communication protocols, which are able to
detect and correct errors in received messages are
applied, and/or data reliability recovery, used for
further processing in each of redundant channels,
is provided.
QUALITY OF FUNCTIONS
EXECUTION
Accuracy
Accuracy requirements are regulated for mea-
suring channels of the I&C system and SHC,
which display, register, archive and / or transmit
numerical values of physical quantities in allowed
for them units, for control channels (protection,
interlocking, regulation) and alarm, and also (on
agreement between a developer and operating
organization or a customer) for components of the
I&C system and component parts of SHC, forming
measuring channels, control and alarm channels.
During standardization and estimation of ac-
curacy the following rules are followed:
Accuracy of measuring channels
is specified
in form of metrological characteristics of these
channels, to which a measurement range, conver-
sion function, error characteristics are related.
Error characteristics of a measuring channel are
standardized:
• Allowed absolute, relative or conventional
error in working (on agreement between
the developer and the operating organi-
zation or a customer - limit) operation
conditions.
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