Flame detectors receive 335VDC from Mark V panel. I would like to understand what is the voltage level/amplitude of the pulse coming back to control system.
In many of the Operations & Service Manuals provided with GE-design heavy duty gas turbines there was a GE-written description of how the UV flame detector works. If I recall correctly, it basically shorts the 335 VDC input repeatedly based on the intensity of the "flame" (UV radiation) it is exposed to, producing a 0-335 VDC square wave output. So the amplitude of the signal is 335 VDC, and the frequency of the signal is a function of the "flame" (UV radiation) the sensor is exposed to, and the shape of the output is a basically a square wave.
Hope this helps! Try looking in your Operations & Service Manual for a GE-produced document about the Honeywell UV Flame Detectors. I think in later years (in the 1990's) they stopped providing that document, about the time they started mass-producing DLN combustor-equipped units and started using the Reuter-Stokes flame detectors (Silicon-Carbide type). If the document is in your manual, it probably provides a better description.