REFERENCE CHANNEL FOR SENSING OPTICAL CONTAMINATION

摘要

The appts. includes at least one electromagnetic energy detector having at least one surface which electromagnetic energy can strike and an indicator for indicating when the detector detects electromagnetic energy. The appts. also includes at least one test source of electromagnetic energy, each source being disposed near a detecting surface of the detector (S). The intensity of the radiation form the test source is calibrated to cause the detector to detect te test source radiation only when the detecting surface has no more than a predetermined amount of contamination disposed on it. The appts. pref. includes a transparent protective shield disposed over the detecting surface of the detector.