The required id attribute is the QIF id of the measurement resource, used for referencing.
Source
<xs:complexType name="TactileProbeSensorBaseType" abstract="true"><xs:annotation><xs:documentation>The abstract TactileProbeSensorBaseType is the base type that defines a tactile probe. A TactileProbeSensorBaseType is often called a stylus.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="DetachableSensorBaseType"/></xs:complexContent></xs:complexType>