燃气涡轮工程手册 Gas Turbine Engineering Handbook 3(61)

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Temperature below 200 0F (93.3 0C) 0.0F (0.270C)
Temperature above 200 0F (93.3 0C) 1.0 0F (0. 6 0C)
Pressure 0.1%
Vacuum pressure Absolute pressure transmitters recommended
Mass flow of fuel gas 0.8%
systematic errors， and for the propagation of random and systematic uncer-tainties into the uncertainty of a test results. The various statistical terms involved are defined. The end result of a measurement uncertainty analysis isto provide numerical estimates of systematic uncertainties， random uncer-tainties， and the combination of these into a total uncertainty with an approximate confidence level. This is especially very important when com-puting guarantees in plant output and plant efficiency.
The PTC 22 establishes a limit of uncertainty of each measurement required; the overall uncertainty must then be calculated in accordance with the procedures defined in ASME PTC 19.1 Measurement Uncertainty. The code requires that the typical uncertainties be within a 1.1% for the PowerOutput， and 0.9% in the heat rate calculations. It is very important that the post-test uncertainty analysis should be also performed to assure the parties that the actual test has met the requirement of the code.
The instrumentation will be calibrated as per the requirements of the test codes. All the instrumentation must be calibrated before a test and certified that they meet the code requirements. The ASME PTC 19 series outlines the governing requirements of all instrumentation for an ASME Performance Test to be within the governing band of uncertainty.
Table 20-1 is a very short abstract of the test measurement requirements for the performance tests; the ASME PTC 19 series should be the final governing document:
Flow Straighteners
Minimum lengths of straight pipe are required for flow-measuring devices and for certain pressure measurements. Flow straighteners and/or equalizersshould be used in the vicinity of throttle valves and elbows， as shown in Figure 20-1.

Figure 20-1.Flowequalizersandstraighteners. (PowerTestCode10， Compres-sors and Exhausters， American Society of MechanicalEngineers， 1965.)
Pressure Measurement
The following types of instruments are used to make pressure measure-ments:
1.
Bourdon tube gauges

2.
Dead-weight gauges (used for calibration purposes only)

3.
Liquid manometers

4.  
Impact tubes
 . Pitot-static tubes

 

6.
Pressure transmitters

7.
Pressure transducers

8.
Barometers

Good-quality Bourdon tube test gauges are highly suitable for pressure measurements of more than 20 psi. They should be calibrated against a deadweight tester in their normal operating range. When selecting a pressuregauge， it is important to see that the measure value is above midpoint on the scale.
Differential pressures and subatmospheric pressures should be measured by manometers with a fluid that is chemically stable when in contact with the test gas. Mercury traps should be used where necessary to prevent the manometer fluid from entering the process piping. Errors in these instru-ments should not exceed 0.2 %.
A common failure in pressure measurement is the uncertainty of the configuration of static-pressure taps penetration through the pipe wall.This failure is another early-planning concern， since proper taps are easyto provide prior to placing the machine inservice， but inspection of the taps after operation has commenced is a luxury rarely afforded the test team.
Another pitfall in pressure measurement， particularly important in flowmeasurement， is the potential for liquids in gauge lines. All too often gauge lines coming from overhead pipes have no provision for maintaining aliquid-freestatus， even though the flowing fluid may be condensible at gauge-line temperatures.
Calibration of the pressure-measuring device presents another pitfall for test crews. All too often a test is conducted through the field calculation stepbefore bad data reveals that gauges， possibly with too large a minimumincrement， were removed from the shipping carton and installed， relying on the vendor"s calibration. On-site calibration of all instruments is always good insurance against a bad test.
　
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