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We have a Frame 5 DLN machine running on fuel gas with MarkV control and have a problem that all four flame intensity signals fluctuate in all modes. It is higher when in ELL or premix modes but the fluctuations are relatively constant and anywhere from 10 to 50 counts across the detectors. These are new detectors fitted after an overhaul (looking back historically the old detectors did this also). All wiring and earthing has been checked. All fuel valves are stable, fuel gas inlet temperature is ok and all other turbine parameters are ok with no indication of any combustion problems. It has been running like this for three months but due to the fluctuations we keep dropping out of premix mode. The fluctuations are causing the flame intensity signal to catch the thresholds that were set during the DLN tuning. They could be raised but our turbine man is reluctant to change them as the same threshold is used for flame on during primary mode. Any suggestions?