a. Basic sensor: it is the most basic single conversion device.

b. Combined sensor: it is a sensor composed of different single conversion devices.

c. Application sensor: it is a sensor composed of basic sensor or combined sensor and other mechanisms.

For example: thermocouple is a basic sensor, which is combined with the heat absorber that converts infrared radiation into heat to form an infrared radiation sensor, that is, a combined sensor; The application of this combined sensor in infrared scanning equipment is an applied sensor.