element of a measuring system that is directly affected by a phenomenon, body, or substance carrying a quantity to be measured
EXAMPLES Sensing coil of a platinum resistance thermometer, rotor of a turbine flow meter, Bourdon tube of a pressure gauge, float of a level-measuring instrument, photocell of a spectrometer, thermotropic liquid crystal which changes colour as a function of temperature.
NOTE In some fields, the term “detector” is used for this concept.