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Diagnos av stiktion i reglerventiler för prediktivt underhåll
Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, Department of Electrical Engineering.
2009 (Swedish)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesisAlternative title
Diagnosis of stiction in control valves for condition based maintenance (English)
Abstract [en]

This master thesis reviews advances in detection and diagnosis of static friction (stiction) in control valves. Control valves suffering from stiction results in oscillating control loops which in turn decreases both the process stability and reliability. Perstorp AB sees a necessity to automatically detect stiction in valves before the effects of the malfunctioning valves have become too severe. This thesis presents an introduction to maintenance, control loops and how stiction in valves can affect performance of control loops.

A selection of methods presented in the literature are introduced and examined using normal operating data from the site in Perstorp. Common for all selected methods is their intuitive ideas and that they are based on normal operating data and minimum amount of process knowledge. For the adaptive segmentation method a further development is presented where among other things a test quantity is proposed.

This thesis shows that none of the selected methods can reliably diagnose stiction in control valves from normal operating data. Noise in process value and irregular disturbances results in weakened trend characteristics.

Finally, the thesis has tested a root cause analysis of plant-wide oscillating control loops found on two plants in Perstorp AB.

Abstract [sv]

Detta examensarbete är en undersökning av detektion och diagnos av kärvande reglerventiler. Kärvande reglerventiler ger upphov till att reglerkretsar börjar att självsvänga vilket leder till sämre processtabilitet och driftsäkerhet. Perstorp AB ser ett stort behov att automatiskt detektera kärvande ventiler innan deras inverkan har blivit för omfattande. Rapporten presenterar en grundläggande redogörelse för arbete med underhåll, reglerkretsar och hur kärvande reglerventiler som kan leda till sämre reglerprestanda.

Ett selektivt urval av de metoder som har presenterats i litteratur introduceras och analyseras för att utvärderas på driftsdata från anläggningen i Perstorp. Gemensamt för samtliga metoder är att de bygger på intuitiva idéer, normal driftdata och minimal kunskap om processen. För den adaptiva segmenteringsmetoden presenteras en vidareutveckling där bland annat en teststorhet har tagits fram.

Rapporten visar att ingen av de utvärderade metoderna kan tillförlitligt diagnosticera kärvande reglerventiler ur verklig driftsdata då brus i mätsignaler och oregelbundna störningar leder till att karakteristiken hos trenderna försvagas.

Slutligen görs en analys av en metod för att hitta grundorsaken till att flera reglerkretsar svänger på två fabriker inom Perstorp AB.

Place, publisher, year, edition, pages
2009. , 101 p.
Keyword [en]
stiction, diagnosis, control valves, maintenance
National Category
Control Engineering
Identifiers
URN: urn:nbn:se:liu:diva-16539ISRN: LITH-ISY-EX--09/4229--SEOAI: oai:DiVA.org:liu-16539DiVA: diva2:202432
Presentation
2009-01-28, Algoritmen, Linköping, 10:15 (Swedish)
Uppsok
teknik
Supervisors
Examiners
Available from: 2009-03-11 Created: 2009-01-30 Last updated: 2009-03-11Bibliographically approved

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CiteExportLink to record
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