hotplate vs steam generator

hotplate

noun
  • A semi-portable stove. 

  • The element of a stove. 

  • A low-powered heating device for keeping food warm. 

steam generator

noun
  • a type of boiler fitted in a diesel locomotive or another rail vehicle, which provided steam heating in steam-heated passenger trains that had previously been hauled by steam locomotives. 

How often have the words hotplate and steam generator occurred in a corpus of books? (source: Google Ngram Viewer )