Infrared temperature measurement uncertainty for unchopped thermopile in presence of case thermal gradients

This paper analyses the spatial and temporal temperature stabilisation requirements of unchopped thermopile IR pyrometers under different temperature conditions and measurement wavelengths. Each thermopile output signal is affected differently and independently by the appearance of undesired spatial and temporal gradients in a thermopile case structure. Expressions for the ratios of thermopile sensitivity to spatial and temporal gradients versus a change in scene temperature are derived from a simplified static and dynamic thermopile thermal model that takes into account the internal structure and operation of the sensor. The ratios depend on the thermopile and the target absolute temperature, as well as the physical and optical properties of the thermopile. This knowledge may help in selecting the appropriate detector, optimising the design of pyrometer thermal control systems, or in establishing strategies to compensate for the associated uncertainty.