Photo-acoustic sensor for detection of oil contamination in compressed air systems

TL;DR

This paper presents an innovative online photo-acoustic sensor capable of real-time detection of oil contamination in compressed air systems, offering high sensitivity and robustness for industrial applications.

Contribution

The development of a continuous, in-situ photo-acoustic sensor system for detecting oil vapors in compressed air, with demonstrated high sensitivity and stability.

Findings

Standard deviation of 0.3 ppb for decane vapors

Normalized noise equivalent absorption coefficient of 2.8×10^{-9} W cm^{-1} Hz^{1/2}

Effective detection of hexane and decane vapors in real-time

Abstract

We demonstrate an online (in-situ) sensor for continuous detection of oil contamination in compressed air systems complying with the ISO-8573 standard. The sensor is based on the photo-acoustic (PA) effect. The online and real-time PA sensor system has the potential to benefit a wide range of users that require high purity compressed air. Among these are hospitals, pharmaceutical industries, electronics manufacturers, and clean room facilities. The sensor was tested for sensitivity, repeatability, robustness to molecular cross-interference, and stability of calibration. Explicit measurements of hexane (C${_6}$H$_{14}$) and decane (C${_{10}}$H$_{22}$) vapors via excitation of molecular C-H vibrations at approx. 2950 cm$^{-1}$ (3.38 $\mu$m) were conducted with a custom made interband cascade laser (ICL). For the decane measurements a (1 $\sigma$) standard deviation (STD) of 0.3 ppb was demonstrated, which corresponds to a normalized noise equivalent absorption (NNEA) coefficient for the prototype PA sensor of 2.8$\times 10^{-9}$ W cm$^{-1}$ Hz$^{1/2}$.