About: http://webisa.webdatacommons.org/289101258

Property	Value
http://www.w3.org/1999/02/22-rdf-syntax-ns#type	http://www.w3.org/ns/prov#Entity
http://www.w3.org/ns/prov#value	A light source, such as one or more light emitting diodes and a pair of light detectors, such as photodiodes, create a pair of pulse trains whose frequency varies with the speed of rotation.
http://www.w3.org/ns/prov#wasQuotedFrom	google.com