flowrate withinthe pipe.The sensor mayalso providedata in real timeduring
the processor retrospectivelyin the casewheresamples are analysedoff-line.
Tables35.1±35.3summarisethe majorsensingtechniques that havebeenor
couldbe appliedfor foodprocessing. Someof the techniques are still at the
research or developmentstage but are basedon threemaincategories:
- Process parameters,whichcan be usedto provideinformationon plant
process performance. - Measurementof surfacecondition,for example depositthickness.
- Determinationof quantity of materials withinsystem, for example detergent
or biocideconcentration.
In currentcommercialpracticethe mostwidelyused monitoringapproachesare:
∑ visualinspection;
∑ predefined process usingexistingsensorsand detergent conductivity;
∑ heattransfer;
∑ pressuredrop;
∑ ATP;
∑ microbiological;
∑ conductivity.
Table35.1 Measurementof processparameters
Technique Measurement Classifi- Key issues
principle cation
Overallheat Ucalculatedfrom Realtime Assumesuniformdeposit
transfercoefficient,U basicheattransfer Integrated properties
(Visseret al.1997) equationusing Invasive Accuracyof multiple
conventionalsensors instruments
Heatflux Heatflux can be Realtime Reliability,assumes
(Joneset al.1994; calculateddirectly Localised thermalpropertiesof
Truonget al.1998; frompowerinput Invasive deposit,representative
Hastinget al.2005) to sensor location
Potentiallynon-invasive
Pressuredrop Increasein pressure Realtime Accuracyespeciallywhen
(Corrieuet al.1986) dropdue to decrease Integrated pressuredroplow,
in hydraulicdiameter Invasive interpretationof data,
assumesuniformdeposit
thicknessand surface
roughnessknown
Existingprocess Deliveryof minimum Realtime Assumesthat deliveryof
sensors,e.g. acceptableprocess Indirect definedprocesswill
temperature,time, for cleaning/ Invasive assurecleanlinessand
flowrate disinfection adequatedisinfection
Monitoringof fouling, cleaning and disinfection in closedprocessplant 575