Due to the significant advances in CFD (computational fluid dynamics) and CHT (coupled heat transfer) analysis in recent years, gas turbine engineers can design turbine components with higher accuracy in a shorter time. However, since the failure of the rotating parts of the gas turbine can cause catastrophic damage to the gas turbine, it is still of great significance to accurately measure the operating temperature of the blades. This is why gas turbine manufacturers have been working hard to measure blade temperature.

A customized optical pyrometer is an optical device that measures the radiance of the surface of the blade. It uses the Planck equation to calculate the blade temperature. The customized optical pyrometer is usually installed on the outer casing of the gas turbine, and its installation time is very short. As the development cycle of gas turbines becomes shorter and shorter, the measurement of blade temperature in a short period of time becomes crucial. In this regard, the customized optical pyrometer is the most capable device. The pyrometer also has disadvantages because it does not directly measure the temperature, but the temperature is calculated based on the measured radiance. In order to overcome this problem, many researchers have made great efforts, and the pyrometer is no longer a specialized tool.

The most accurate way to obtain the surface temperature is to use a thermocouple embedded in the blade. The output is transmitted via slip ring or telemetry. Since the temperature can be measured directly with a thermocouple, it has the highest accuracy compared to other techniques described later. But wiring in the rotor and data transmission device requires a lot of time and cost. The short life of thermocouples sometimes cannot make up for the cost. The biggest disadvantage is the limitation of measuring points. In recent years, as the turbine inlet temperature has increased, the cooling structure of the blades has become more and more complicated. Therefore, the limited number of measurement locations is not enough to fully understand the temperature distribution on the blade surface.

TIP (Thermal Index Paint) is also commonly used. Although it can be used and the cost is reasonable, it has the following shortcomings; I) Assemble the painted blades, conduct engine tests, peel off the engine, and watch the paint color change, which takes a lot of time. 2) Real-time monitoring is not possible. Iii) The temperature resolution is poor.