Martin Degner

High resolution led-spectroscopy for sensor application in harsh environment

The usage of novel LED-light sources for spectrometric application is shown and described in this paper. The utilization of fiber optical linkage to a simple open path absorption cell and a proper control of the light sources is the key to a robust and high resolved measurement system. A novel optical sensor system based on this approach is realized to measure the concentration of nitrogen dioxide, sulfur dioxide with a resolution below 1 ppm and ozone down to 30 ppb at a 4 cm single reflection cell in a fraction of a second measurement time. In this setup the emitted light from Light Emitting Diodes in the ultraviolet to the visible wavelength range was used. The optoelectronics and the control electronics are separated from the optical sensor head where the pure optical sensor effect takes place. Therefore the sensor can be used in harsh environment for instance in an exhaust tailpipe system or close to discharge plasma in strong electromagnetic fields or at high temperature. Furthermore the sensor design is potentially low cost, quite small, long life and well suited for a large number of applications - from small battery powered hand held devices to industrial process control implementation. An LED-based sensor does not compete to laboratory chemical analytical devices but in many cases it is well suited for high resolved and fast online concentration measurements.

Low cost sensor for online detection of harmful diesel combustion gases in UV-VIS region

Online detection of harmful exhaust gases is necessary for optimal engine control to reduce the polluting emissions of diesel cars. Optical detection methods in the UV-VIS range enable the simultaneous characterisation of various gases such as NO, NO2 and SO2. Additionally this technique is fast and has a low cross-sensitivity to other exhaust components. First results show the advantages for the optical approach compared with standard electrochemical gas sensors.

Novel sensor cell design and algorithm to online realize stable and cost effective optical concentration measurements at fluctuating light source situations

The spectroscopic optical absorption technique is widely used for estimation of substance concentration. It is based on the wavelength specific determination of light extinction in an absorption cell that is caused by the interaction of light with the molecules of the claimed substance. The absorption measurement is an indirect method because a light attenuation (often only at a few spectral measurement points) is used. This measurement is not only influenced by the substance absorption but also unwanted by disturbances and changes of light emission, guiding and receiving. New optical methods for realizing an online reference for a robust absorption measurement has been designed and investigated. Compared to commonly used methods the designed technique is not complex but effective and also well suited for small sensor application. The utilized concept is based on the variation of the effective absorption path length within a sensor cell in a simple way. Stable absorption measurements at the presence of strong spectral changes of the light source intensity are shown here to demonstrate the potential of the developed technique.

Micromirror array based optical spatial filter technique for fast and flexible velocimetry

Spatial filtering technique is an optical method for measurement of the relative velocity between the sensor and the observed surface(s). This technique is well known for tens of years, its benefits are a potentially simple optical setup and low requirements to the data acquisition and analysis. Therefore it is a valuable method for online contactless velocimetry. The classical spatial filtering setup is based on a static grating in the optical detection path with at least one or two photodetectors. Newer developments are using line array or two-dimensional detectors (e.g. CCD or CMOS). Here the grating structure is realized by weighting the pixels in a signal pre-processing. The flexibility of adapting the grating to the application is much higher but the detector speed of the array sensors is much lower than that of the photodetectors in the classical setup. Both properties are important for a spatial filter sensor that can be used in a wide range of application. The novel micromirror array based optical spatial filter design that is presented in this paper combines the advantages of both state of the art systems. It utilizes fast photodetectors in combination with a very precise, flexible and high resolved differential grating that is realized by the micromirror array. The present paper gives a short overview on the spatial measurement technique, explains the micromirror array based sensor approach and shows the proof of concept.

Optical fibre sensors for the monitoring of harmful emissions from land transport vehicles

In order to meet increasingly stringent emission control laws it is necessary to develop a sensor that can accurately monitor the level of pollutants entering the atmosphere from land transport vehicles. These pollutants are generally a mixture of hot gases and particulates. An optical fibre sensor is particularly well suited to this task. Due to its small size and weight it is minimally invasive making it suitable for insertion into the vehicles exhaust system. Optical fibres are immune from poisoning by the analyte gases, although they do require shielding from airborne particulates. As they do not transmit electricity they are also highly safe and furthermore they are immune from electromagnetic interference. To detect the presence of the gases it is proposed to use an optical absorption technique. The majority of gases of industrial and environmental importance have their fundamental absorption line in the mid-infrared region of the electromagnetic spectrum, with weaker overtones in the near infrared. Due to the greater availability of components, optimised for communications, most optical fibre gas sensing has taken place in the near-infrared region of the spectrum. In this paper mid-infrared optical fibre gas sensing techniques are investigated and the results of the investigation are presented. Due to the inhomogeneous state of the gas flow it is necessary to measure temperature especially just upstream of the after-treatment section where this can rise to as high as 650oC with large temporal gradients. Measurements of temperature of hot gases from a full size test engine using an optical fibre probe based on fluorescence decay time measurements are also presented.

UV Emitters in Gas Sensing Applications

The LED-based spectroscope is described. Example measurements using the gases O3, SO2, and NO2 are given. The unique properties of UV-LEDs are utilized in combination with standard broadband photodiodes (PD). These low-cost components can be arranged in a simple design which produces cost-effective but high-resolution sensors compared with current state-of-the-art measurement systems. Broad UV absorption lines/bands are well suited for UV emitter-based sensing.

Evaluation of a micromirror array based sensor system for optical velocity measurements using the Spatial Filter Velocimetry approach

Today, digital micromirror devices (DMD) are mainly used for multimedia applications like image or video projection and in some cases for structured light measurements. But like most optical devices, DMDs can also be used in the opposite direction to collect the light from an object instead of illuminating it. This paper shows the potential of DMDs for velocity and path measurement applications based on the well known spatial filter technique. Used as a spatial filter, the DMD combines the advantages of a fixed grid (fast, high dynamic range) with the flexibility of structured receivers like CCD- or CMOS-Matrix sensors.

Vibration-insensitive temperature sensing system based on fluorescence decay and using a digital processing approach

A fluorescence-based temperature sensor system using a digital signal processing approach has been developed and evaluated in operation on a working automotive engine. The signal processing approach, using the least squares method, makes the system relatively insensitive to intensity variations in the probe and thus provides more precise measurements when compared to a previous system designed using analogue phase-locked detection. Experiments carried out to determine the emission temperatures of a running car engine have demonstrated the effectiveness of the sensor system in monitoring exhaust temperatures up to 250°C, and potentially higher.

Safety and applicability of a pre-stage public access ventilator for trained laypersons: a proof of principle study

BackgroundContemporary resuscitation guidelines for basic life support recommend an immediate onset of cardiac compressions in case of cardiac arrest followed by rescue breaths. Effective ventilation is often omitted due to fear of doing harm and fear of infectious diseases. In order to improve ventilation a pre-stage of an automatic respirator was developed for use by laypersons.MethodsFifty-two healthy volunteers were ventilated by means of a prototype respirator via a full-face mask in a pilot study. The pre-stage public access ventilator (PAV) consisted of a low-cost self-designed turbine, with sensors for differential pressure, flow, FO2, FCO2 and 3-axis acceleration measurement. Sensor outputs were used to control the respirator and to recognize conditions relevant for efficiency of ventilation and patients’ safety. Different respiratory manoeuvres were applied: a) pressure controlled ventilation (PCV), b) PCV with controlled leakage and c) PCV with simulated airway occlusion. Sensor signals were analysed to detect leakage and airway occlusion. Detection based upon sensor signals was compared with evaluation based on clinical observation and additional parameters such as exhaled CO2.ResultsPressure controlled ventilation could be realized in all volunteers. Leakage was recognized with 93.5% sensitivity and 93.5% specificity. Simulated airway occlusion was detected with 91.8% sensitivity and 91.7% specificity.ConclusionThe pre-stage PAV was able to detect potential complications relevant for patients’ safety such as leakage and airway occlusion in a proof of principle study. Prospectively, this device provides a respectable basis for the development of an automatic emergency respirator and may help to improve bystander resuscitation.