2. Minimizing degradation and maintaining operation near design effi-ciencies.
3.
Diagnosing problems， and avoiding operating inregions， which could lead to serious malfunctions.
4. Extending time between inspections and overhauls.
5. .educing life cycle costs.
.iagnostic System Components and Functions
1. Instrumentation and instrumentation mountings
2. Signal conditioning and amplifiers for instrumentation
3. Data
transmission system (cables， telephone link-up， or microwave)
4.Data
integrity checking， data selection， data normalization and storage
5. Baseline generation and comparison
6. Problem detection
7. Diagnostics generation
8. Prognoses generation
9. .n-site display
10.Systems for curveplotting， documentation， and reporting
.ata Inputs
.btaining good data inputs is afundamental requirement， since any analysis system is only as good as the inputs to the system. A full audit of the various trains to be monitored must be made to obtain optimum instru-mentation selection.
The factors that need to be considered are the instrumenttype， its meas-urementrange， accuracy requirements， and the operational environmental conditions. These factors must be carefully evaluated to select instruments of optimum function and cost to match the total requirements of the system.For instance， the frequency range of the vibration sensor should be adequate for monitoring and diagnostics and should match with the frequency range of analysis equipment. Sensors should be selected to operate reliably andaccurately within the environmental conditions that prevail (for example， whenused on high-temperature turbine casings). .esistance temperature sensors，with their higher accuracy and reliability compared to thermocouples， may be necessary for analysis accuracy and reliability. Calibration of instrument-ation should be conducted on a schedule established after reliability factors have been analyzed.
All data should be checked for validity and to determine if they are within reasonable limits. Data that are beyond predetermined limits should be discarded and flagged for investigation. An unreasonable result or analysis should set up a routine for identification of possible discrepant input data.
Instrumentation .e.uirements
It is essential that instrumentation requirements be tailored to the require-ments of the machine being monitored.However， the instrumentation requirements should exist to cover the requirements for both vibration and aerothermal monitoring.
Any existing instrumentation should be used if found to be adequate. While there are advantages in the use of noncontacting sensors built into the machine for measurement of journal displacements， this instrumentation is often impossible to install in existing machinery. Suitably selected and located accelerometers can adequately cover the vibration-monitoring requirements of machinery. Accelerometers are often an essential supple-ment to displacement sensors to cover the higher frequencies generated bygearmesh， blade passing，rubs， and other conditions.
Typical Instrumentation ..inimum .e.uirements for Each .achine.
(.ote: .ocations and type of sensors depend on the type of machine under consideration.)
1. Accelerometer
a. At machine inlet bearingcase， vertical
b. At the machine discharge bearingcase， vertical
c. At machine inlet bearingcase， axial
2. Process pressure
a. Pressure drop across filter
b. Pressure at compressor and turbine inlet
c. Pressure at compressor and turbine discharge
3. Process temperature
a. Temperature at compressor and turbine inlet 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：燃气涡轮工程手册 Gas Turbine Engineering Handbook 3(47)
