related to foodquality control, and havebeenwellcovered elsewhere(Kress-
Rogers and Brimelow, 2001).
Lookingat the heart of a sensor system, the sensor element,the task of this
apparatus is to respond to a physical stimulusby producing a signal (the sensor
is a typeof transducer) that providesdirector indirect information aboutthe
status quo (Fig.19.1).The classificationof sensor systems results fromtheir
material, the operatingtemperature or theirsignal/measurementcategory (e.g.
thermal energy, electromagneticenergy, acousticenergy, pressure,magnetism
or motion).
As for all analytical instruments, the critical performance requirements for
sensor systems are sensitivity, reproducibility and selectivity. Furthermore
industrialneedshaveto be taken intoaccount, i.e. fast measurementtimes,
Table19.1 Overviewof physicalsensorsusedfor foodindustrialpurposes
Parameter Sensorprinciple/sensor
Temperature Resistance/Pt-100sensor
Flow Volumetric/positivedisplacementsensorsand turbinemeters
Electromagnetic
Mass/Coriolismassflowmeters
Pressure Resilience/ceramicsensors
pH/redoxvalue/ion Potentiometric/Ag/AgClelectrode
concentration Conductivity/two-electrodesensorwitha givencell constant
Inductivesensors
Turbidity Optical/opticalsensor
Processstatus Ultrasonic/ultrasonicsensor
Microwave/propagationof microwaves
Moisture/dewpoint Dielectricity/polymerdielectricsensor
Fig. 19.1 Generalworkingprincipleof chemicalsensorsand biosensors.288 Handbookof hygiene controlin the foodindustry