Table35.2 Measurementof surfacecondition
Technique Measurement Classifi- Key issues
principle cation
Ultrasound Attenuationof Realtime Sensitiveto temperature,
(Withers1996) ultrasoundvelocity Localised particles,gas bubbles.
betweentwo sensors Non- Limitedresolutionof
invasive depositthickness
ATP Detectionof organic Retro- Assumespresenceof
materialson contact spective organicmaterialsindicates
surfaces Localised microorganisms
Invasive Calibrationrequiredfor
eachsoil
Microbiologicalassay 1. Swabbingto detect Retro- Limitedaccess,significant
microorganisms spective timedelay,representative
Localised samples.Presenceof
Invasive coliformsindicatorof poor
hygiene/cleaning
- End product Retro- Significanttimedelay,
sampling spective unlikelyto detectlow
Localised contaminationlevels.
Invasive Difficultto differentiate
fromothercauses
Surfaceelectrical Depositconductivity Realtime Calibration,implementation
properties Localised on processareas
(Galeand Griffiths Invasive
1995)
Visual Surfacecondition Retro- Simple,minimalequipment,
spective accuracyand resolution,
Localised subjectiveassessment,
Invasive non quantitative
Optical Scatteringof light Retro- Accessto process
(Bartlettet al.1997; (opticalor near spective surfaces,sensitivity
Tamachkiarowaand infrared)beamor Localised threshold
Flemming1999) pulsesduring Invasive
transmissionthrough
filmof deposit
Pneumaticgauging Approachof air or Realtime
(Gale1995, liquidjet to surface Localised
Tuladharet al.2000) is monitoredby Invasive
changein pressure
576 Handbookof hygiene controlin the foodindustry