Flame Ionisation Detector

A flame ionisation detector converts a hydrocarbon gas concentration into an electrical signal. The flame is hydrogen fuelled and burns in hydrocarbon free combustion air. Either side of the flame are two electrodes between which an electric field is generated by means of a polarisation voltage. The sample is pre-mixed with the fuel gas and heated in the flame to a temperature at which the hydrocarbon molecules ‘crack’ and CH fragments appear. These CH fragments are oxidated by the oxygen in the combustion air resulting in the formation of CHO+ ions. The ion current then passes to the electrodes and the resulting current measured is proportional to the quantity of C atoms derived from organic compounds.

The Thermo-FID features two seperate microprocessor controlled pressure compensations to avoid any influence from environmental or sample conditions. In addition, the complete Thermo-FID range of analysers are equipped with a flame trap that is used as a heated sample inlet filter. The measurement chamber and all material in contact with the sample gas are heated between 120°C and 200°C to avoid condensation.