Abstract: An electrostatic instrument for measuring particle concentrations and possibly sizes in aerosols, such as an Electrostatic Low Pressure Impactor or Differential Mobility Analyser suffers from errors which limit the useful response bandwidth of the device. The invention minimises or eliminates these transient errors which are caused by changing particle concentrations in the aerosol. A system may be added to an otherwise conventional instrument to compensate for the transient effects based on a model of the charge production mechanism. Alternatively, a screening electrode placed over the sense electrodes in the instrument, and held at controlled electrical potential difference, is added to the instrument to eliminate the effect. A third embodiment adds compensating electrodes which provide a direct measurement of the transient effect which can be subtracted from the signal.

Abstract: A flame ionization detector comprises a housing forming a flame chamber for burning a mixture of hydrogen, oxidant and a sample gas. The flame chamber includes: a nozzle in which the sample gas and hydrogen are intimately mixed prior to injection, an igniter for igniting the gas emitted from the nozzle, inlets for hydrogen and oxidant, and an exhaust outlet through which the burnt gases are removed. A collector electrode is electrically insulated from the housing of the flame chamber. The nozzle and flame chamber housing are electrically grounded, and the collector electrode is maintained at a predetermined potential relative to ground. A pre-chamber is disposed adjacent to the flame chamber to provide a substantially constant pressure input of the sample gas to the nozzle.