Limits of IR-spectrometers based on linear variable filters and detector arrays

Abstract

Linear variable filter (LVF) spectrometers represent an interesting group of low cost spectral monitoring systems for procedural or condition monitoring systems. Such highly integrated, miniaturized spectral devices are promising components for the design of rugged, portable and shock resistant monitoring systems. Among others, detection of chemical substances and their corresponding concentrations in fluids is possible by analyzing the characteristic absorption bands. Using this spectral device for lubricant condition monitoring a certain quality of spectra is essential for revealing the change of their properties over lifetime. The focus of this work is to evaluate the useability of a low cost chip-size wavelength interrogator having a 256 elements pyroelectric detector array combined with a linear variable filter. Therefore, simulations were performed to specify the maximum resolution and to compare it to real world measurement data in the petrochemical domain. The influence of a different number of detector elements per array (e.g. 64 / 128) on the maximum spectral resolution is calculated and compared to measured data. An ideal system design is presented and the limits of such interrogators with respect to infrared spectral monitoring are indicated.