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Light Intensity Adjustments
FREE WATER DETECTOR (AEL MK I AND AEL MK II)

Aviation Boatswains Mate F - Aviation theories and other practices
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Figure 3-7.—AEL Mk III (rear view). retighten the nuts on the bulb holder. Refasten the back of the instrument. Calibrating the AEL MK III The AEL Mk III comes with 2 WRATTEN calibration filters that are wrapped in silver foil. A Wratten calibration filter set is a pair of filters with a known contamination value. The filters must be kept in their silver foil wrappers so dust does not affect the readings you get. The reason you have to calibrate an AEL Mk III is that you get wear on the photovoltaic cell, which will give you improper readings if not constantly checked. NOTE Calibrate quarterly or when a part is replaced according to PMS. When you handle the filters, use FORCEPS. The area of contact should be within 1/4 inch of the edge of the filter to avoid damage to the filter’s surface. The calibration should be done in the following manner: 1. Turn on the light and let it warm up for at least 3 minutes. 2. Adjust the light intensity, using the rheostat knob, until the milliammeter scale reads 0.6. 3. Pickup one Wratten filter, using the forceps. Lift the photocell (or slide out the plate) and insert the filter into the receptacle. Replace the photocell (or slide in the plate) and record the milliammeter reading in the log book. 4. After logging your results, remove the Wratten filter and put it back into the foil wrapper. 5. Readjust the rheostat, if the milliammeter reading is not 0.6. 6. Repeat steps 3 and 4 with the second Wratten filter. 7. To obtain calibration point, subtract the lower of the two milliammeter readings from the higher reading. This difference is plotted on the calibration chart versus the weight of contaminant per liter given for the set of Wratten filters. A second point is plotted at 0 milligrams per liter and 0.01 milliamps change in light reading. Example (fig. 3-6): a. Filter contamination factor = 1.6 milligrams per liter. b. Difference between Wratten filters = 0.04 milliamps. c. Plot this point with the calibration chart. d. Plot second point where 0 milligrams per liter and 0.01 milliamps BISECT. 3-19







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