4.1.2 Efficiency instrumentation
These are instruments required to determine or infer the operating efficiency of the plant, both for short term monitoring and the detection of long term trends.
The temperatures and pressures of steam and water are measured to confirm that the plant components are operating efficiently and in the intended manner. For example, measurement of the steam and water conditions at the inlet and outlet of a feedwater heater enables an operator to confirm its satisfactory operation. Unsatisfactory operation is unlikely to prejudice the continued running of the plant but does affect its efficiency. This category of instrumentation therefore draws attention to maintenance activities which are efficiency-related.
Alarms are derived from some parameters in this category, for example, steam temperatures upstream of the HP stop valves. These alarms are less critical than those derived from supervisory instrumentation and therefore the alarm processing may be carried out exclusively in the data processing computer. Steam temperatures upstream of the turbine HP stop valves are used to provide data for the long term history.
Some of the parameters in the efficiency instrumentation category are used for the heat rate test instrumentation identified in the condition monitoring category. The requirement for accurate, calibrated instruments for a heat rate test often precludes the use of the same transducers as those used for efficiency instrumentation.