Vesda VSP-031 VLI Secondary Filter Spare PartThe VLI detector combines a fail safe Intelligent Filter (patent pending) with an advanced clean air barrier for optics protection allowing the use of absolute detection and a long detection chamber life without the need for recalibration. The Intelligent Filter: reduces the level of pollution in the air sample before it enters the detection chamber, which dramatically extends the operational life of the detector in harsh and polluted environments. is