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Whitepaper Draft V0_1_1
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MOST DISCUSSED PARAGRAPHS
P40 • Dead volume 1For non-flush-mounted transdu
P42 • Capacitance vs. temperature 1This may be g
P7 Outline:This chapter shall present currently
P23 Piezoelectric transducers for dynamic pressu
P26 Transverse means that the charge is collecte
P29 Piezoelectric pressure transducers offer man
P36 Sensing MechanismAdvantagesDisadvantagesCapa
P37 Outline:This chapter should contain an overv
Pressure transducer should be although as near as possible to the hot gas, to avoid wave distortion due to non-linear effect. I think it is better to develop in this direction, rather than to try to develop a sensor which should sustain > 700 °C. The sensor can be placed in the volume with cooling air. Such layout can also allow to install several sensors (for redundant), and it may also be possible to send calibration signal from outside
I agree the comment of Lukas, and it is important. For a stationary signal (like combustor pulsation measurement) polarity is not important (so far all applied sensors are equipped with a same chain), but for a transient measurement, (like compressor surge, or rotating stall) it is important to note the polarity. When the sensor producer supply also an amplifier, the polarity of voltage signal should be noted.
Initial draft version
Formatting and outline tweaks
CGG Calcium Gallium Germanium crystal group. Usually the short form for Ca3Ga2Ge4O14 crystals
CRP Capacitive Response to Pressure
CRT Capacitive Response to Temperature
EMI Electromagnetic Interferance
Endevco Endevco ®
EVI-GTI European Virtual Institute for Gas Turbine Instrumentation
FBG fibre Bragg grating
FPI Fabry-Pérot interferometer
FSO Full Scale Output
ISA Instrumentation, Systems, and Automation Society formerly known as Instrument Society of America
Kistler Kistler GmbH
Kulite Kulite Semiconductor Products Inc.
MDS Minimum Detectable signal
Meggitt Meggitt SA
Oxsensis Oxsensis Ltd.
PCB PCB Piezotronics Inc.
Piezocryst Piezocryst Advanced Sensorics GmbH
RMS Root-Mean-Square, Root-Mean-Square
Measuring dynamic pressures within the varying environmental conditions of gas turbines is extremely complex due to the high-level understanding of the numerous pressure sensor technologies available, fluid mechanics, data acquisition and analysis required in order to collect accurate, reproducible dynamic pressure data. Selecting the appropriate pressure transducer to measure dynamic pressure complicates the matter as there are numerous pressure sensor technologies available, such as piezoresistive, piezoelectric, optical, capacitive, resonant, etc., all of which have different advantages and limitations.
A survey conducted prior to the writing of this document showed, that there is in fact a necessity to improve comparability and reduce complexity in the matter of dynamic pressure measurement. A first step is to take and review the prior work on the topic of standardization of dynamic pressure measurement in gas turbines to find areas for improvement. The following document is based on the work of the dynamic pressure measurement subcommittee of the European Virtual Institute for Gas Turbine Instrumentation (EVI-GTI) and aims to take the already existing work and add new content as an impulse to continue working on the topic. During a workshop with various stakeholders regarding dynamic pressure measurements in gas turbines the general consensus suggested that a first step towards standardization will be to start with a whitepaper or guideline where essential needs, terms, specifications and best practices can be found. This document is intended to provide inputs for further developments in this direction and present best practices that may be followed within the industry. The scope of this document is to:
This chapter shall present currently employed transducer technologies with their advantages and disadvantages. Each technology shall be described within 2 pages to maintain readability. The following content has already been created and can be used for further work.
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Nowadays various approaches for measuring dynamic pressure are pursued by transducer manufacturers. The most common technologies used, in alphabetical order, are capacitive measurement, optical measurement, piezoelectric measurement, and piezoresistive measurement.
Capacitive methods for measuring pressure, in general, rely on the basic principle of plate capacitors. The capacitance of a plate capacitor is influenced by the area of the plates, the distance from one plate to the other, and the insulation material. The capacitance of a capacitor can be calculated using Eq. below.
For a simple pressure transducer, only the distance between the plates is influenced by pressure changes. By the nature of a capacitive pressure transducer, such deformations are induced by pressure changes acting on the membrane. A schematic of a capacitive pressure sensor can be seen in Fig. 2.1 below.