TDLAS/WMS Embedded System for Oxygen Concentration Detection of Glass Vials with Variational Mode Decomposition

Abstract

Whether the oxygen content for medical glass vials can be measured accurately affects greatly the ingredient stability of sterile pharmaceuticals. Tunable diode laser absorption spectroscopy (TDLAS/WMS) based on wavelength modulation has the remarkable advantages of non-contact, low cost, high sensitivity, real-time response, which shows great potential in the field of in-site oxygen concentration detection. Due to the short optical path and various environmental disturbances, it is challenging to measure the headspace oxygen concentration in open-path optical environment. Targeting this challenge, this paper designs a TDLAS/WMS-based gas concentration sensing architecture and turns it into an embedded detection system. Then, a robust signal reconstruction method based on variational mode decomposition (VMD) is established to suppress the random noise of the demodulated harmonic signal. Hence, the oxygen concentration can be reliably inversed from the peak-to-peak values (Vp-p) of the 2nd harmonic signal. This detection framework is abbreviated as WMS+VDM+Vp-p. Encouragingly, the preliminary application on a glass vial encapsulation line demonstrate that the proposed method performs promising results with an absolute detection error of within ±1.5% and a minimal Allan deviation of 0.0010@(100s), which provides a good start for the on-site headspace oxygen concentration measurement for pharmaceutical glass vials.