Ir sensor with reflective calibration

Abstract

A self-calibrating infrared (IR) sensing device having the capability to measure the attenuation effects of surface contamination on the transmission window and to adjust the gain of the sensor accordingly so as to counter the attenuation. The IR sensing device includes an IR sensor mounted in a housing having an IR transparent window that allows IR radiation originating from outside the housing to be directed toward the sensor. The IR sensor includes a thermally isolated area of IR-absorbing material coupled to a temperature measuring unit. IR radiation impinging on the sensor is absorbed, thereby raising the temperature of the IR absorbing material. The temperature measuring unit measures the increase in temperature and generates a proportional electronic signal indicative of the temperature. The electronic signal is received and processed by a processor. An IR radiator is also included within the sensing device housing. When activated, the radiator emits IR radiation that passes through the window and is lost to the outside if there is no contamination. If the surface of the window is contaminated, the radiation raises the temperature of the contaminants. This increase in temperature results in a return signal (i.e., IR emissions from the contaminants) that is detected by the sensor. A mirror element is also included within the sensing device. The mirror element focuses radiation from the remote target onto the sensor, and it reflects IR radiation emitted by the IR radiator onto the window. The magnitude of the return signal indicates the amount of contaminant on the surface of the window. The return signal is detected and measured by the IR sensor, and is used to signal a warning and/or determine the amount of gain necessary to compensate for the loss of true signal caused by the presence of the contamination.