Thermal management in pyrometer modules for automotive applications

Abstract

Thermopile pyrometer modules are the state of the art for contactless temperature measurement in automotive applications. Here sensors have to operate precisely in a challenging thermal environment. While the compensation of the steady state ambient temperature is a well known technique in thermopile radiation temperature sensors, transient thermal effects are still an issue. The change of the ambient temperature as well as temperature flow through the sensor can lead to substantial errors due to unwanted thermal gradients within the device. In the thermopile chip they leads to an error signal since the measurement principle is based on quantifying thermal gradients of the chip that result from the detected IR-radiation. Thermal gradients in the cap and between cap and thermopile chip lead to an exchange of heat radiation between thermopile chip and cap that is erroneously detected and thus also leads to errors. Different methods were developed that separately or in combination allow for a significant improvement of the accuracy and signal stability. The methods are based on the reduction of thermal gradients within the thermopile chip and the entire sensor device (isothermal, high thermal mass cap), reduction of radiation exchange between the sensor chip and the housing (low emissive inner cap surface) and prediction and software compensation of the error signal.