| 摘要 |
PURPOSE:To achieve highly accurate detection, by jointly using two modes, one for detecting fine foreign matters and the other for relatively large foreign matters. CONSTITUTION:A P polarization component and an S polarization component are converted with respective detectors 8 and 9 into electrical signals corresponding to the quantity of light and the detector 8 is connected to a comparator circuit 10 while the detector 9 to a divider 12. The circuit 10 sends the signal by the P polarization component to a comparator circuit 11 and a divider 12 only when it exceeds a threshold P0. The circuit 11 sends a high-level detection signal to an OR gate G1 only when the signal from the circuit 10 exceeds a threshold P1 (when a foreign matter is detected) and a high-level foreign matter detection signal indicating the existence of a foreign matter is sent from an output terminal. The divider 12 sends a signal P/S based on the electrical signals P and S to a comparator circuit 13, which inputs a high-level signal into the gate G1 only when the signal exceeds a threshold M (when a foreign matter is detected) to output a foreign matter detection signal. This enables highly sensitive detection of fine and relatively large foreign matter simultaneously. |
