Institute of Electrical Measurement and Signal Processing

Capacitive Flowmeter for Gas-Solids Flow pApplications Exploiting Spatial Frequency

Daniel Hrach, Anton Fuchs, and Hubert ZanglDaniel Hrach, Anton Fuchs, and Hubert Zangl

Graz University of Technology

I tit t f El t i l M t d M t Si l P iInstitute of Electrical Measurement and Measurement Signal Processing

Kopernikusgasse 24 / IV, 8010 Graz, Austria

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Institute of Electrical Measurement and Signal Processing

A dAgenda

Introduction State of the Art Granular Flow Sensors Capacitive Correlator Capacitive Spatial Filter Advanced Excitation Scheme Experimental Setup Conclusion

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Institute of Electrical Measurement and Signal Processing

I t d tiIntroduction

P ti iPneumatic conveying:

Solid particles in gas clean, flexible and

reliable conveying solutionsolution

applicable for coal dust, wooden- or plastic ppellets, salt, sugar, flour, ...

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Institute of Electrical Measurement and Signal Processing

State of the Art Gran lar Flo SensorsState of the Art Granular Flow SensorsOptical:

PIV PIV problems with dust

Ultrasonic: doppler shift works only in special cases (low particle number, problems

with sound distribution in the pipe material) GGamma rays: correlative principle expensive personal security import/export environmentexpensive personal, security, import/export, environment, ..

Capacitive: correlative or spatial filtering principle

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Granular flow measurement is challenging!

Institute of Electrical Measurement and Signal Processing

Capaciti e CorrelatorCapacitive CorrelatorCorrelative principles can also be used with light, gamma rays, magnetic principlesp p

Two sensor positions with known distance inwith known distance in flow direction result in a time shifted measurement signalmeasurement signal

velocity = sensor distance

T

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

T

Institute of Electrical Measurement and Signal Processing

C iti S ti l FiltCapacitive Spatial Filter

P i i l ll k i Principle well known in

optics

Pipe interior seperated Pipe interior seperated

into a regular array of

different sensitive areas

Particles with constant

velocity cause quasi

periodic signal

velocity = electrode distance1

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

velocity = electrode distance . T

Institute of Electrical Measurement and Signal Processing

Capaciti e Spatial Filter IICapacitive Spatial Filter II

many concurrent y

particles in the

volume cause large

offset capacity

low signal powerg p

advanced excitation

pattern required

velocity = electrode distance2

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

velocity = electrode distance . T

Institute of Electrical Measurement and Signal Processing

Advanced Excitation Scheme

FEM Simulation shows:

lower number of periods

f mean free measurement signal

increased signal increased signal power

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Institute of Electrical Measurement and Signal Processing

Experimental Setup

variable speed fan

pellets with a diameter of 3 mm and a permittivity of about 3

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Hot film anemometer

Institute of Electrical Measurement and Signal Processing

Experimental Setup II

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Institute of Electrical Measurement and Signal Processing

Experimental Setup III

in-/quadrature phase

measurement

sampling rate approx.

8 kHz

Particle velocity

determination by means

of frequency estimation

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Institute of Electrical Measurement and Signal Processing

Experimental Setup IV

Periodogram calculation:

Frequency estimation

using overlapping FFTs

higher airflow velocity

(higher particle number)

causes higher amplitude

in frequency spectrum

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Sensor principle works!

Institute of Electrical Measurement and Signal Processing

Concl sionConclusion

Non invasing measurement system for particle velocityg y p y Based on capacitive spatial filtering Advanced excitation pattern presentedp p Differential excitation allows higher gains Laboratory test results presentedy p

Principle of spatial filtering IS applicable to capacitive fl tflow measurement

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter

Institute of Electrical Measurement and Signal Processing

Capacitive Flowmeter for Gas-Solids FlowCapacitive Flowmeter for Gas Solids Flow

Applications Exploiting Spatial Frequency

Thank you!

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Daniel Hrach SAS 2008, Atlanta, 12 Feb 2008 Capacitive Flowmeter