Environmental Engineering Reference
In-Depth Information
fact that each channel (main and backup) is pow-
ered from its own secondary source, while these
sources are hooked up to two different primary
electric power supply networks. Power for the
input/output modules of analogue and digital
signals is also made redundant in this manner.
In this case the failure of any network does not
lead to disturbance of DPU functioning, because
power of one of the channels is preserved. For the
same reason, redundant equipment of the higher
level, which are supplied directly from the 220
V alternating current network, are hooked up to
different networks of the primary electric power
supply. Power of non-redundant operator stations
is arranged so that if there is failure of any one of
the networks and each workstation serviceability
is retained by any one of two operator stations
(hooked up to the good network).
Hardware diagnostic devices of SHC and the
design solutions adopted ensure the possibility of
quickly discovering failures and timely restoration
of serviceability of any stations. In particular, the
replacement of failed modules in the DPU can be
done without disconnecting power and does not
require installation following replacement.
DPU technical diagnosis is achieved by hard-
ware devices (watch dog) and diagnostic programs
as part of the library of standard programs, which
are supplied by Westinghouse (level of diagnostics
is up to one interchangeable module). Technical
diagnostics of higher level stations is achieved
by programming devices of the workstations and
commercial personal computers. Diagnostic mes-
sages are transmitted over the local network and
are displayed on the workstation video monitors.
Accuracy of the nformation functions is defined
by the accuracy of sensors with continuous (ana-
logue) output signals and measurement channels of
the SPDS, which accomplish conversion, storage,
transmission and display of data in digital form.
In this case the main part of the error of informa-
tion system measurement channels is that due to
errors of sensors.
Limits of acceptable value of the assumed er-
ror rate of the SHC measurement channel under
operating work conditions do not exceed ± 0.5%
for signals of the thermocouples and thermistors
± 0.3% for signals of sensors with uniform current
and voltage output.
For the inputting and conversion to digital
code of signals from sensors in the measurement
channels of the SPDS highly accurate modules
QRT are used (for the input of four signals from
the thermal resistance converters) and QAX (for
input of 12 channels from the remaining sensors).
Automatic calibration with “zero” correction and
conversion factor of all conversion channels of
input signals of a given module is accomplished
every 8 seconds in the QAX modules and every
9 seconds in the QRT modules, that is built into
the microcomputer modules. Limits of accept-
able values of the induced error rate of signal
conversion in the QAX or QRT module do not
exceed ± 0.1%, and the “zero” drift per month is
not more than ± 0.002%, long term drift is not
more than ± 0.02%.
Temporal characteristics of the SPDS:
• Duration of the data input cycle from sen-
sors of continuous and discrete signals
(with deterministic access) - 0.1 and 1.0
seconds;
Quality of Functions
•
Time resolution capability for input of
continuous and discrete signals -- not more
than 0.02 seconds;
Requirements for quality of functions include:
• Accuracy requirements;
•
•
Rate of data refreshing, displayed on moni-
tor screens, once per second;
Requirements on temporal characteristics;
•
Requirements
for
the man-machine
interface.
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