Monitoring of oil aerosol contamination in pressurised air with SnO2-based thick film sensors in real life conditions

The oil aerosols in pressurised air, originating from a typical screw-type compressor, are vapourised by a slow isotherm expansion through a capillary; the resulting oil vapour is applied to different SnO2-based thick film sensors placed at ambient pressure. The sensor resistances correlate with the oil content, the best performing sensor shows a 75% decrease of the resistance when the oil content reaches 30 mg oil/m3, a critical threshold value. A set up based on a real compressor was designed and put together for proving the concept. It was operated for more than 18 months with the same sensors still showing comparable performance. Baseline changes can be observed, mostly correlating with changing ambient conditions as observed by parallel reference analytics (r.h., T, …).