.yrometers

The use of pyrometers in control of the advanced gas turbines is being investigated. Presently all turbines are controlled based on gasifier turbine exit temperatures or power turbine exit temperatures. By measuring the blade metal temperaturesof the first stage nozzles andblades， the gasturbine is being controlled at its most important parameter. In this manner， the turbine is being operated at its real maximum capability.
Gas turbines can be ordered with ports for pyrometer measurements of the first stage nozzle and blades. Pyrometers have been able to detect which blade is running hot. In a particular case a blade was found to be running about 50 0F (28 0C) hotter than the rest of the blades. The blade upon inspection was found to have its cooling passages blocked. This led to the manufacturer changing their inspection techniques.
.ressure .easurement
Almost all gas turbines are equipped with pressure-measuring devices ofsome type， although the number and location may vary. These transducers consist of a diaphragm and strain gauges. When pressure isapplied， the deformation of the diaphragm is measured by the strain gauges. The resulting output signal varies linearly with pressure changes over the operating range.
Because of temperature constraints， the transducers， which usually do not operate above 350 0F (177 0C) are located outside the engine. A probe is then located inside to direct the air to the transducer. Most manufacturersprovide probes to measure the compressor inlet pressure， compressor exitpressure， and the turbine exhaust pressure. These probes are usually locatedalong the shroud of the machine， and therefore， the pressure readings may be slightly in error due to boundary-layer effects.
In addition to these standardlocations， it is recommended that probes be located at each bleed chamber in the compressor and on each side of the airfilter. These new locations are not intended to measure the unit performance， but are used to diagnose problem areas.
By using dynamic pressure probes in the bleed chamber， it is possible to detect tip stall. A pressure rake at the compressor exit enables accurate read-ings of exit pressure and is also helpful in the diagnosis of compressor stall.
Pressure transducers must be located outside of the engine because of temperature constraints. A pressure transducer can typically withstand tem-peratures up to 350 0F(177 0C)， which is quite low with respect to the temperature of the points to be measured. The electrical output of the transducer will be in the m.j. range and therefore must be amplified and conditioned for interfacing to the monitor system. The locations are as follows:
1.  Compressor inlet. Unit is constructed of Chromel-Alumel (nickel alloy) and characterized by an exposed junction consisting of a bare wire with ceramic insulation. .ne unit is required here.

2.  Compressor discharge. Same as compressor inlet thermocouples. .ne or two units required in this area.

3.  Turbine inlet temperature. Thermocouple is constructed of platinum-platinum rhodium with the junction enclosed with ceramic insulation.Typically， 9-12 units are required at this stage.

4.  Turbine e.haust. Thermocouple is constructed of Chromel-Alumel with an exposed junction. .ine to 12 units are required at this stage.

.ibration .easurement
.ibration measurement is described in detail in Chapter 16. To monitora machine for vibration problems， the use of displacementprobes， velocitypickups， and accelerometers must be used to describe fully the mechanical behavior of a machine. Displacement probes measure the movement of the shaft at the location of the probe. They cannot be used very successfully to measure shaft bending away from the probe location. Displacementprobes can indicate problems such asunbalance， misalignment， and some subsynchronous vibration instabilities such as oil whirl and hysteretic whirl.Accelerometers， since they are mounted on the casing， pick up the spectrum vibration problems which are transmitted from the shaft to the casing.Accelerometers are used to diagnose many problems， especially those thathave a high frequency response， such as blade flutter， dry frictional whirl，surge， and gear teeth wear. .elocity pickups are used for their flat response of amplitude as a function of frequency as a gojno-go device. This means that the setting to alert the operator can be the same regardless of the speed of the unit. The role of velocity probes as a diagnostic tool is somewhat limited. The velocity pickups are very directional.they read different values for the same force if the probe is placed in a different direction.
　
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