Non-Contact Temperature Measurement Using Thermopile Detectors

Non-Contact Temperature Measurement Using Thermopile Detectors

Introduction:
One of many applications of the thermopile detector is the remote measurement of temperature. In this Application Note we explain the basic principles of remote temperature measurement. Every object at temperature T (above absolute zero – 273.15°C) emits electro-magnetic radiation. The total amount of power or radiant flux (Ф) emitted per unit solid angle and per unit area over all wavelengths is given by the Stefan-Boltzman law.

Thermopile detectors respond to thermal energy emitted by any object in its field of view by producing a voltage that is proportional to incident power. This response is called the responsivity (R) of the detector.

The net power exchange between an object (source or target) and a thermopile is influenced by the following factors:

• temperature of the source Ts and detector Td;
• area of detector and source, as well as the shape, orientation, and distance between them;
• additional objects in the path (for example: optics);
• the radiative characteristics of all surfaces, such as emissivity;
• medium between detector and an object (for example: atmosphere and moisture).

Please see the pdf application note to find out the math behind this.