Martin Liess

Temperature radiation sensors for automotive climate control

We present the different applications with their critical to success parameters and show how the demands can be met using innovative techniques, such as miniaturized sensor assemblies with integrated pre-amplification, ambient temperature compensation and housing with high thermal mass.

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.

Error reduction during visual processing by the retina—a paradigm for sensor design

We use a general second-order mathematical description of sensing, sensory information acquisition and pre-processing to treat biological vision in analogy to a technical sensor. Using very early visual processing by the retina, i.e. the retinal receptive fields, we compare the structure of interconnection of photoreceptors, bipolar and ganglion cells that evolved in vertebrates with other structures of interconnections that would serve the same purpose of generating an image of contrasts and supplying it to the brain. We are able to show that the ladder-type structure of the vertebrate retina approaches ideal behaviour (with respect to high linearity and low error sensitivity) and is the structure most tolerant to imperfection of its constituent elements, the different nerve cells. Since the model presented is very general, it can be applied to other sensory systems as well. The application of the sensory structure of the retina (which, from the biological modelling point of view, derives in a straightforward way from known facts about retina physiology) is useful if applied to sensor design. In particular it shows how nonlinearities, error- and cross sensitivities of the entire sensor system can be reduced by the structure among its elements.

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.

A simple and high effective tellurium based sensor for NO/sub 2/ detection

A simple and stable NO/sub 2/ gas sensor device with rapid response/recovery time and low operating temperature has been developed using polycrystalline tellurium. The effect of thickness of the sample, thermal treatment and temperature to sensitivity against NO/sub 2/ is presented for the first time. The sensitivity strongly increases with thickness of the film decreasing, especially at thickness less than 100 nm. Thermal treatment of the films (at temperatures greater than 100/spl deg/C) and increasing of operating temperature above 80/spl deg/C result in decrease of sensitivity to NO/sub 2/, while it strongly improves the response and recovery times. By conditions of best compromise between the main sensing parameters, achieved at operating temperature 50/spl deg/C, there are no noticeable drifts of baseline or of gas induced current. The sensing mechanism is explained by interaction of adsorbed species with lone-pair electrons, which form the upper part of the valence band.