Jürgen Dr. Schilz

Thermal Management in Pyrometer Modules for Automotive Applications

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.

Stabilization of the output signal of thermopile sensors in the thermal environment of automotive applications

Thermopile pyrometer modules are the state of the art for contactless temperature measurements in automotive applications. In such an application, the thermopile has to operate precisely in a challenging thermal environment. While the compensation of the steady state ambient temperature is a well known technique when using thermopiles for temperature measurments, 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 lead 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 the cap and the thermopile chip will lead to an exchange of heat radiation between the thermopile chip and the cap, which also leads to measurement 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.

Integration and miniaturization of thermopile-based pyrometric module construction sets

We present the main applications for contact-less (radiation-) temperature measurement with thermopile sensors and show how the large number of different requirements associated with them can be matched using a low-cost sensor module construction set in a TO39 housing. The main components are: A choice from different MEMS-thermopile sensors or sensor arrays, one of two programmable ASIC’s, IR optical components to be integrated, such as filters, IR lenses, a Winston cone reflector and different caps. Of the latter, a significant innovation is the isothermal cap, which integrates the mechanical functionality of a cap with optical functions such as the reduction of ghost images and most importantly the thermal functionality of a massive heat sink. This way a complete pyrometer can be build into a TO39 housing.