Environmental Engineering Reference
In-Depth Information
• Allowed main (absolute, relative or con-
ventional) error under normal test condi-
tions and allowed additional errors, which
can be caused by a change of each EIF in a
range of speciied for it working or limiting
values.
Accuracy of alarm and control channels
is
specified in a form of accuracy characteristics
of these channels in working and limit operation
conditions. Accuracy characteristics include limits
of an allowed absolute error of output and with-
drawal of a command (output signal) and limits
of allowed relative error of formation time lags
and / or dwells if they are provided in algorithms
of performance of control functions.
For the I&C system, an absolute error of output
and withdrawal of a command (output signal) is
determined as a difference between an actual value
of a controlled parameter, caused the indicated
action, and a specified value (set-point) of this
parameter, under which such an action should be
executed. For SHC during determination of an
absolute error instead of a controlled parameter,
values of an informative parameter of a proper
analog input signal are considered. Relative er-
ror of formation of a dwell (lag) is calculated as
a ratio of an absolute error (difference between
an actual and a specified value) to a specified
dwell (lag) value. As an actual value a result of
a direct estimation of a dwell (lag) is accepted
using measurement facilities.
Limits of allowed absolute errors of output
(withdrawal) of commands and output signals
and relative errors of formation of dwells and lags
during a change of any EIF in a range of regulated
for its limiting values are determined on agree-
ment between the developer and the operating
organization or the customer. For confirmation
of compliance of alarm and control channels with
specified requirements, checks of characteristic
accuracy during a trial operation and periodic
control during a preventive and predictive main-
tenance are provided.
Conventional error of a measuring channel is
calculated as a ratio of an absolute error to a range
of monitored parameter change. Absolute error is
determined as a difference between a measured
and actual value of a monitored parameter, where
a measured one is considered a parameter value:
directly obtained for a data base; displayed or
registered in a digital or analog form; calculated
by an output signal; transmitted in an output
digital signal (message). For the I&C system as
an actual value of a monitored parameter a result
of its estimation by use of measurement facilities
is accepted, for SHC - by a measured value of a
proper analog Input signal, considering a nominal
static characteristic of the signal source (sensor,
normalizing transducer, etc.).
Accuracy requirements of measuring chan-
nels are established by agreement between the
developer and operating organization (customer),
where metrological characteristics of updated
I&C systems and, first of all, contained in them
SHC, are usually significantly higher than previ-
ously operated ones had. Before commissioning,
all measuring channels of the I&C system pass
metrological certification according to require-
ments of state standards of Ukraine.
In grounded cases, instead of metrological
characteristics of measuring channels, metrologi-
cal characteristics of component parts, which are
determined for assurance of a metrological com-
patibility of these component parts that allows
defining metrological characteristics of measuring
channels by a calculation method, can be regu-
lated. Experimental estimation of metrological
characteristics of component parts of measuring
channels is executed during their development,
after manufacturing and during operation.
Timing Performances
Timing performance is determined for each of the
main functions of the I&C system and SHC in a
form of nominal or maximal permissible (upper
and / or low) values:
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