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Whitepaper Draft V0_1_1

Starting: 14 Apr Ending

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P1

Whitepaper Draft

Towards a Standard in Measuring Dynamic Pressure in Gas Turbines

Version 0.1.1

Changelog

Table 0.1: Changelog

P2

Version

Date

Comments

0.1

02.03.2021

Initial draft version

0.1.1

17.03.2021

Formatting and outline tweaks

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P3

Figure 2.1: Scematic of a capacitive pressure transducer. [18]............................3

Figure 2.2: Schematic of a sensor head using light interferometry. [5].......................5

Figure 2.3: Cut drawing of a transverse piezoelectric pressure transducer. [6, p. 83].............6

Figure 2.4: Two different builds of piezoresistive pressure transducers, left the traditional method and right a new approach to increase sensor performance. [21] 8

Figure 6.1: Proposal for a standardized 9.5 mm plug type transducer reference shape............23

Figure 6.2: Proposal for a standardized miniature transducer reference shape.................24

Figure 7.1:Three cable termination solutions by Kistler. From left to right: LEMO®PCA.0S.302, 7/16”-27 UNS-2A and open leads. [10] 28

Figure 8.1: Common best practices: Schematic of a threaded boss for high frequency, flush mounted dynamic pressure measurements. [41] 31

Figure 8.2: Common best practices: Schematic of a modular flange and boss for high frequency, flush mounted dynamic pressure measurements. [41] 31

Figure 8.3: Recess mounted pressure transducer. [41]................................32

Figure 8.4: Common best practice: Scematic of a semi-infinite tube for DC ~10kHz frequency, high temperature (600-1500°C) dynamic pressure measurements. [42] 32

Figure 12.1: Angle of incidence. [42]............................................36

Figure 12.2: Operational space of a static and dynamic pressure transducer. [28]..............39

Figure 12.3: Comparison of static, quasi-static, and dynamic pressure.......................41

Figure 12.4: Total pressure, static pressure and dynamic pressure.........................41

Figure 12.5: Sensitivity, linearity deviation and hysteresis for a piezoelectric sensor. [21].........46

Figure 12.6: Temperature Gradient Error and Temperature Error. [6]......................52

Figure 12.7: Recess mounted pressure transducer. [21]...............................54

Figure 12.8: Example - MEMS packaging related resonances. [21].........................55

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

RSS Root-Sum-of-Squares

P4

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.

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P5

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:

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P6

  • Provide a general overview of the fundamental sensor technologies used in the numerous dynamic pressure transducers available.
  • Demonstrate applications for dynamic pressure measurement within gas turbines.
  • Develop standardized datasheet content for the different transducer technologies based on existing ISA standards (e.g. ISA-S37.1 [1],ISA-S37.10 [2], and ISA-S37.3 [3]).
  • Standardize the specifications and validation/calibration testing methods used to define the dynamic performance of the various pressure transducer technologies to improve industry wide understanding of underlying technologies and capabilities based on the former mentioned ISA standards.
  • Present standardized transducer shapes that have been derived from existing widespread transducers.
  • Give an overview of currently employed electrical connectors and aspects towards standardization in this area.
  • Provide an overview of different mounting methods for dynamic pressure transducers together their individual advantages and disadvantages.
  • Develop an accelerated lifetime testing procedure for transducers used in gas turbines.
  • Implement transducer health check procedures for transducer users.
  • Describe the operating conditions within gas turbines as well as identify and address common problems encountered when making dynamic pressure measurements and recommend solutions to overcome such industry problems.
  • Establish terms and definitions for clear communication within the document and between users of the document.

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P7

Outline:

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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P8

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.

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P9

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.

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P10

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P11


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.

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