Zusammenfassung In diesem Beitrag wird die Kalibration eines kompakten optischen Sensors für die Online-Ölzustandsüberwachung in Verbrennungsmotoren vorgestellt. Der Sensor basiert auf dem Prinzip der nicht-dispersiven Infrarotspektroskopie (NDIR-Spektroskopie) und misst die Absorption in sieben verschiedenen Spektralbereichen. Mit Hilfe multivariater Regressionsmethoden werden lineare Modelle erstellt, die den Zusammenhang zwischen infraroter Absorption und wichtigen Ölzustandsparametern, wie beispielsweise Wassergehalt, Oxidation, Sulfation und Basenzahl, beschreiben. Die Validierung der Modelle anhand eines Datensatzes von Gebrauchtölproben aus unterschiedlichen Anwendungen zeigt eine gute Übereinstimmung mit Referenzwerten aus einer Laboranalyse. Durch den Einsatz von Kalibrationstransferverfahren können die erstellten Regressionsmodelle auf einem zweiten Sensor gleicher Bauart angewendet werden, wobei sich die Prädiktionsgüte nur geringfügig verschlechtert.

In this article, the design and application of an optical sensor for fluid monitoring based on two tunable Fabry-Perot filters is presented. The sensor enables fluid transmission measurements in the spectral ranges from 1818 cm(-1) to 1250 cm(-1) and from 1250 cm(-1) to 952 cm(-1) at wavenumber-dependent resolutions between approximately 20 cm(-1) and 33 cm(-1). A novel method is proposed to ensure a correct wavenumber representation of the obtained spectra, correcting for an oblique light path in the optical system. The sensor shows high linearity and a low noise level for absorbance measurements. As an example for a fluid monitoring application, the transmission spectra of deteriorated automotive engine oil samples were measured and compared to spectra obtained with a Fourier-transform infrared spectrometer. We used partial least squares (PLS) regression to construct calibration models for the prediction of significant oil condition parameters, like oxidation, sulfation, water content and viscosity, from the obtained spectra. The values predicted from the absorption spectra show high correlation with reference values of the oil condition parameters determined in a laboratory according to appropriate standards. These results indicate that the sensor can be a useful supplementary tool for fast and cost-effective engine oil condition monitoring. (C) 2017 Elsevier B.V. All rights reserved.

The condition of lubricating oil used in automotive and industrial gearboxes must be controlled in order to guarantee optimum performance and prevent damage to machinery parts. In normal practice, this is done by regular oil change intervals and routine laboratory analysis, both of which involve considerable operating costs. In this paper, we present a compact and robust optical sensor that can be installed in the lubrication circuit to provide quasi-continuous information about the condition of the oil. The measuring principle is based on non-dispersive infrared spectroscopy. The implemented sensor setup consists of an optical measurement cell, two thin-film infrared emitters, and two four-channel pyroelectric detectors equipped with optical bandpass filters. We present a method based on multivariate partial least squares regression to select appropriate optical bandpass filters for monitoring the oxidation, water content, and acid number of the oil. We perform a ray tracing analysis to analyze and correct the influence of the light path in the optical setup on the optical parameters of the bandpass filters. The measurement values acquired with the sensor for three different gearbox oil types show high correlation with laboratory reference data for the oxidation, water content, and acid number. The presented sensor can thus be a useful supplementary tool for the online condition monitoring of lubricants when integrated into a gearbox oil circuit.

Online monitoring of gases in industrial processes is an ambitious task due to adverse conditions such as mechanical vibrations and temperature fluctuations. Whereas conventional Fourier transform infrared (FTIR) spectrometers use rather complex optical and mechanical designs to ensure stable operation, static FTIR spectrometers do not require moving parts and thus offer inherent stability at comparatively low costs. Therefore, we present a novel, compact gas measurement system using a static single-mirror Fourier transform spectrometer (sSMFTS). The system works in the mid-infrared range from 650 cm - 1 to 1250 cm - 1 and can be operated with a customized White cell, yielding optical path lengths of up to 120 cm for highly sensitive quantification of gas concentrations. To validate the system, we measure different concentrations of 1,1,1,2-Tetrafluoroethane (R134a) and perform a PLS regression analysis of the acquired infrared spectra. Thereby, the measured absorption spectra show good agreement with reference data. Since the system additionally permits measurement rates of up to 200 Hz and high signal-to-noise ratios, an application in process analysis appears promising.

Zusammenfassung Statische Einzelspiegel-Fourier-Transformations-Spektrometer ermöglichen Spektroskopie mit hohen Messraten im mittleren infraroten Spektralbereich, da sie geringe interne Lichtverluste aufweisen und gleichzeitig auf bewegliche Teile vollständig verzichten. In dieser Arbeit wird ein solches Spektrometer vorgestellt, optimiert und auf seine maximale Messrate hin untersucht. Ausgestattet mit einem ungekühlten Mikrobolometerarray als Detektor erlaubt es Bildwiederholraten bis 200 Hz bei einer Auflösung von 7.1 cm –1 im Spektralbereich zwischen 1250 cm –1 und 650 cm –1. Durch die hohe thermische Zeitkonstante des Mikrobolometerarrays ist für quantitative spektrale Messungen die Messrate des Gesamtsystems auf 15 Hz zu reduzieren.

Zusammenfassung In diesem Beitrag wird ein kompakter optischer Sensor für die Online-Ölzustandsüberwachung in Verbrennungsmotoren vorgestellt. Er basiert auf dem Prinzip der nicht-dispersiven Infrarotspektroskopie (NDIR-Spektroskopie) und misst die Absorption in sieben verschiedenen Spektralbereichen. Durch die Kalibierung mit einem linearen Regressionsmodell ermöglicht er die Messung wichtiger Ölzustandsparameter, wie beispielsweise Wassergehalt, Oxidation, Sulfation und Basenzahl. Die Messergehnisse von einem Gebrauchtöldatensatz mit drei verschiedenen Motoröltypen weisen eine gute Übereinstimmung mit Referenzwerten aus einer Laboranalyse auf.

Fourier transform spectroscopy has established itself as the standard method for spectral analysis of infrared light. Here we present a robust and compact novel static Fourier transform spectrometer design without any moving parts. The design is well suited for measurements in the infrared as it works with extended light sources independent of their size. The design is experimentally evaluated in the mid-infrared wavelength region between 7.2 μm and 16 μm. Due to its large etendue, its low internal light loss, and its static design it enables high speed spectral analysis in the mid-infrared.

Microbolometer arrays allow spectral analysis of infrared light using static Fourier transform spectrometers (sFTS). Here we evaluate limitations of common-path and single-mirror sFTS regarding their spectral bandwidth.

Zusammenfassung Zur flächigen Schichtdickenbestimmung von lateral bewegten Schichtsystemen wurde erstmals ein Messsystem basierend auf dem reflektometrischen Messprinzip in Kombination mit einem Hyperspektralimager entwickelt. Eine Vorsatzoptik mit integriertem Auflichtpfad formt eine Messlinie, deren Reflexion am Messobjekt auf den Eingangsspalt des Hyperspektralimagers abgebildet wird. Aus den spektralen Daten der Reflektanz wird die Schichthöhe jedes örtlich auflösbaren Pixels des zu untersuchenden Objekts rekonstruiert. Bewegt sich das Messobjekt lateral linear gleichförmig, ergeben zusammengesetzte Messlinien eine Messfläche.

This paper presents an approach of an innovative measurement principle for the quality control of viscous materials during a manufacturing process based on fluorescence imaging. The main contribution to the state of the art provided by this measurement system is that three equal fluorescence images of a static or moving viscous object are available in different optical paths. The independent images are obtained by two beam splitters which are connected in series. Based on these images, it is possible to evaluate each image separately. In our case, three optical bandpass filters with different center wavelengths of 405 nm, 420 nm, and 440 nm were used to filter the separate fluorescence images. The developed system is useable for the detection of impurities in the micrometer range. Further, incorrect mixing ratios of particular components and wrong single components in the viscous materials can be detected with the setup. Moreover, it is possible to realize static and dynamic measurements. In this case the maximum speed of the objects was 0.2 m/s for the dynamic measurements. Advantages of this measurement setup are the universality due to the use of optical standard components, the small dimension and the opportunity to integrate it easily into ongoing processes. In addition, the measurement system works on a non-contact basis. Thus, the expense for maintenance is at a very low level compared to currently available measurement setups for the investigated application. Furthermore, the setup provides for the first time a simultaneous analysis of more than one component and the detection of impurities concerning their nature and size in a manufacturing process.