well suited for flame detection each phototransitor 104 is isolated from the combustion pressure in the sample tube 22 by means of a respective pressure sealing optic rod 108 only one of which is shown each of these rods 108 is beaded at one end and potted into the light sensor housing 98 with epoxy the beaded end 110 oriented toward the sample tube 22 in order to protect these glass rods 108 from the hot combustion products a sacrificial window 112 made of acrylic plastic is glued into a milled slot 114 in the bottom edge of the light sensor bank housing 98 beneath each light sensor 96 these windows 112 must be replaced after each test the light sensor bank housing 98 is preferably made of yellow brass and is machined with a male dovetail to match the corresponding groove 70 in the sample tube 22 as noted above the length of the groove 70 in the sample tube 22 is such that when the sample tube 22 and the light sensor bank 72 are mated the light sensors 96 are automatically aligned with the sight holes 74 provided in the sample tube 22 to permit the measurement of changes in luminosity associated with flame front passage the light sensor bank housing 98 has a top flange 116 which is joined to the fin like portion 98 of the housing at a right angle the flange 116 is secured to each of the two clamping bars 88 by means of four high.