Photoionaisation is a new detection principal utilized in leak testing, specifically for VOC’s (such as Iso-butane, paint thinners, dry cleaning solvents, and some petroleum fuels such as gasoline and natural gas). ION SYSTEMS has successfully automated systems in operation using this technique, capable of detecting leaks down to only 1 x 10-6cc/s in a speed equating to one part every 8 seconds.

Principle of Operation

The components are automatically fed onto the conveyor, where simple pick and place systems load them into specifically designed test chambers. Once loaded the chambers are closed, and purged of residual gasses to ensure clean-room conditions for testing to take place.

Low flows of air are passed around the product, collecting any of the leaked gas, which is then carried to the detector for analysis. Should the level of gas be too great, then a ‘fail’ is recorded for that part.

Once testing is completed, the chambers are opened allowing the pick and place units to remove the parts and place them in the appropriate chute (PASS/FAIL), whilst the next batch of parts is loaded into the waiting chambers.

The Photionisation Detector

A relatively new detector the PID uses advanced technology developed to detect changes in the chemical composition of any atmosphere, caused by volatile organic compounds (VOC’s).

To do this, the sample gas stream is passed through a chamber illuminated by UV light from a lamp. As the VOC’s absorb the light, ions are generated. These ions are then attracted towards a pair of electrodes. The electric current required to neutralise the ions at the electrodes is then amplified and measured.

PID is capable of determining VOC’s to a sub-ppm level. Some selectivity is disseminated by the choice of UV Lamp. The performance of any PID involves a loss of resolution as the concentration increases culminating in a saturation response at the few thousand ppm level for a typical organic.

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