Thermal analysis is an important condition monitoring technique in which temperature sensors are used to determine the presence of a developing fault in a mechanical asset.
Temperature sensors range from simple thermocouples that measure the temperature at one location to infrared cameras that can capture the heat map for a whole area.
Thermocouples use the Seebeck effect: if two wires made of different metals are joined at one end, a change in temperature will produce a voltage across the other, unjoined, ends of the wires. Thermocouples come in different combinations of metals, each with its own temperature range. They also come in sheathed and unsheathed versions, depending on whether they’ll be exposed to corrosion, oxidation and other hazards.
Thermal cameras use Planck’s law: any object with a temperature above absolute zero emits infrared radiation, and the amount increases with temperature. (Infrared radiation is the same phenomenon as ordinary light—just at wavelengths outside our visible range. Radio waves and x-rays are other sections of this same electromagnetic spectrum.) Thermal cameras come in handheld and mounted types; for realtime insight, you’ll need them permanently installed. Accuracy can be affected by the camera’s focus and by how reflective the surfaces being filmed are, as well as air currents and the ambient temperature. Thermal cameras also need a source of power, either wired or from batteries.
The captured infrared signal is directly converted into a color map inside the camera. Each color in the image represents a different temperature. To identify fault-related changes over time, thermal analysis uses the techniques of computer vision, a field of machine learning focused on interpreting images.
Below is a P-F curve demonstrating how thermal analysis compares to other condition monitoring techniques when it comes to fault detection in advance of an asset breakdown. This is a P-F curve for bearing failure in a specific production system.
The locations of the various technologies on the curve will be different for each piece of equipment, production environment and failure mode, so be sure to calculate it for the specific assets and types of degradation you want to monitor.