Abstract: A method of detecting contaminants on a window surface of a viewing system comprises the steps of: reflecting light off of contaminants on the window surface; capturing the reflected light in an image; converting the image into image data; and processing the image data to detect the contaminants on the window surface. Also, apparatus for detecting contaminants on an external surface of a window of a viewing system comprises: at least one light source for reflecting light from contaminants on the external surface; an imager for capturing an image of the reflected light and converting the image into image data; and a processor for processing the image data to detect the contaminants on the external surface.

Abstract: A method of detecting a combustion chemical in a region and setting an alarm based on concentration levels of the combustion chemical comprises the steps of: monitoring the region for a combustion chemical with a sensor having a measurable parameter which changes in value proportional to concentration levels of the monitored combustion chemical, the measurable parameter being ambient temperature dependent; generating an ambient temperature measurement of the sensor; reading the measurable parameter and ambient temperature measurement; processing the measurable parameter and ambient temperature measurement readings to generate a temperature compensated concentration level of the monitored combustion chemical; and setting an alarm based on the generated temperature compensated concentration level. A fire detector unit for implementing the foregoing described method is also disclosed.

Abstract: A light input energizes an optical transmitter providing a light output to a waveguide indicating a process variable. The transmitter has a process variable sensor generating a sensor output. An electrical circuit receives the sensor output and generates an electrical transmitter output indicating the process variable adjusted by a changeable parameter stored in the electrical circuit. The electrical circuit has an input energizing the circuit. An LED converts the electrical transmitter output to the light output. A gallium arsenide photodiode converts a first portion of received light into electrical energy provided to the energization input and converts a second portion of the received light into an electrical output controlling the stored parameter.