6-8] 



INFRARED SYSTEMS 

 n-/2 7r/2 



345 



V2 



3/2 TT 



27r 



(c) 



Fig. 6-36 Target Tracking. 



to such a value that a circular scan of, say, |° results (see Fig. 6-36). Then 

 as long as the image in space of the detector rotates around the target 

 without touching it (Fig. 6-36a) no output (error signal) will result. When 

 the line of sight moves and the detector then encounters the target (Fig. 

 6-36b) an output pulse will result; by comparing the phase of this pulse with 

 a synchronizing signal generated on the shaft of motor 2, an error signal is 

 generated. By having the entire optical detection device movable in the 

 aircraft and motor controlled, these error signals can be used to keep the 

 device pointed at the target. 



In Fig. 6-36c a simplified on-off control is illustrated. The synchro- 

 nizing pulse alternately activates and deactivates the control motors. If 

 the target pulse occurs during an active period, the motor moves the optical 

 system. In Fig. 6-36c the pulse occurs where both the down and left 



