Chapter 7 — BASIC FIRE CONTROL 



other words, this test determines the time re- 

 quired for the computer to arrive at correct 

 relative motion rates. Time required must be 

 small, but smoothness of tracking must also be 

 considered. The rate control system is a com- 

 promise between these two factors. 



Rate control tests consist of tracking a 

 hypothetical motionless target with the computer 

 set for a selected sensitivity of rate error 

 detection. Sensitivity is controlled by the time 

 constant input to the rate control system. Initially 

 a large error is introduced and the time motor 

 is started. Time required to reduce the error 

 by a preselected percentage is timed by a stop- 

 watch. This stopwatch reading is a measure of 

 the actual time constant or sensitivity of the 

 system. It is compared against the theoretical 

 value for the test. 



RANGE 



^. ' j T' J ' .<-\ .-■ '»'h. ' i . ' in r 



TACTICAL RANGE RECORDER 



The tactical range recorder (TRR) shown in 

 figure 7-16 is among the oldest underwater fire 

 control instruments in the Navy. In the event 

 of a casualty to the primary fire control system, 

 the TRR is a fairly reliable auxiliary means of 

 directing depth charge and hedgehog attacks. The 

 introduction of newer fire control systems and 

 such weapons as ASROC, however has resulted 

 in a deemphasis on using the TRR as an aid in 

 firing weapons. The TRR still is a useful aid, 

 though, for classifying sonar contacts as sub- 

 marine or nonsubmarine, and for determining 

 target motion. Because of the broad scope of the 

 subject of classification, only a brief discussion 

 of the TRR is given here. More detailed informa- 

 tion on the use of the TRR is contained in Sonar 

 Technician G 3&2. NP 10131. 



Range Rate 



The traces on the recorder paper show target 

 range versus time. From the traces you can 

 determine range rate and target aspect. Range 

 rate is the relative speed at which your ship is 

 closing the target. Target aspect is the target's 

 heading in relation to your ship. 



The recorder paper moves downward at a 

 constant rate, representing time. The stylus is 

 synchronized with the sound pulse transmissions, 

 and moves across the paper from left to right. 

 When a target echo is received, the stylus burns 

 a trace on the paper that represents target 

 range, as illustrated in figure 7-17. 



To determine range rate, turn the plotter 

 bar until the parallel lines on the plotter bar 



71.64 

 Figure 7-17.— TRR target traces. 



extension match the slope of the traces, then 

 read the speed on the range rate scale. When 

 measuring range rate, use only the latest 200 

 yards of traces, that is, only those traces 

 nearest the top of the paper. Refer to figure 

 7-18. 



Because range rate is a clue to target aspect, 

 which gives an indication of the target's heading, 

 you may wonder about the reliability of range 

 rate. For the greatest accuracy in determining 

 range rate, you must know your ship's speed, 

 and the ship must be headed at the target. 

 Meeting these two conditions is not always 

 possible, consequently you must have some other 

 means of determining aspect. 



Figure 7-18. 



71.65 

 Determining range rate. 



127 



