Aviation Electronics Technician 1 - Historic Naval Ships Association

IR to Composite Video ConversionFigure 6-12 is a diagram showing the optics andelectronic components of a typical receiver-converterrequired to perform IR detection and conversion intoa useable video signal. Although the signal opticalpath and conversion coincide, each path is discussedseparately for simplicity. You should refer tofigure 6-12 as you read the following paragraphs.SIGNAL OPTICAL PATH.— Incoming IRenergy from a target enters the receiver through awindow and strikes one side of a double-sided scanmirror. This mirror is controlled by a seamer module.The IR signal either strikes the mirror directly or isfocused onto the mirror by optical lenses contained inwhat is called an afocal optics unit. The operation ofthe afocal unit is governed by a field of view (FOV)switch on the operator’s infrared detecting set control(IRDSC). In the wide FOV mode of operation, theafocal optic lenses are not in the signal optical path.In the narrow FOV mode of operation, the lenses arein the path shown in figure 6-12. The lenses arefocused by a motor that is controlled by a focusingmodule in the receiver-converter assembly. Thefocusing module has two inputs to control theoperation of the focusing motor. One input is a targetrange scale set by the operator on the IRDSC. Theother input is a feedback signal from a temperaturesensingcircuit in the afocal optics unit. Because theindex of refraction of an optical lens changes withchanges in temperature, the focusing modulemonitors the temperature of the lens and maintainsproper focusing of the IR signal onto the scan mirror.The scan mirror is controlled by a scannermodule. It is also positioned in line-of-sight (LOS)position, along with the entire receiving head, byFigure 6-12.-FLIR optical path and IR processing.6-10