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Show ii) Flicker Frequency Fig 3, below shows a typical flicker spectrum for a coal and oil flame in a traditional PF burner system. A frequency filter, removed the lower boiler frequencies 7 - 10 Hz combustion clouds up to 200 H z and the flame flicker for combusting small particles at around 250 - 2000 H z was used to determine flame condition i.e is a flame present? This allowed, in traditional burners, a very wide range of frequencies to select in commissioning and setup of the instrumentation to provide optimum performance. The almost coincidence of the flame flicker spectra for coal and oil meant that a large gain adjustment was not required, only enough automatic gain compensation to allow for build up of a grime on the window. Fig 4 shows the widest variation found between coal types and ranks demonstrating very clearly that the range 250 to 2000 H z was ideal. The flicker frequency data combined with positional data from the cross correlation technique ensures with absolute certainty there is a stable flame in the ideal position. Fig 3 FREQUENCY, kHz FLICKER SPECTRA JSH/22.8.97 4 |