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(thermometer),comparestheprocessvalue(roomtemperature)withthecommandvariable(desired
roomtemperature)andusestheactuator(changeableresistance)tomanuallyregulatethemanipulated
variable(heatingcurrent),inordertocompensateforthedisturbancevariable(temperaturedropfrom
openingthewindow).Thepersonisthereforethecontroller.
Thecontroldeviceisformedfromtheactuatorandthecontrol.
Thecontrolandcontrollertogetherformtheregulatingdevice.
Thefollowingpicturegivesanabstractportrayalofthesituationdescribedabove.
Thecomparingelementusesthesensortocomparethecommandvariablewiththeprocessvalue.Ifthe
commandvariablesandprocessvaluedeviatefromoneanother,thisresultsinapositiveornegativeloop
errorthatinturnchangestheprocessvalue.
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