468 REGULATORY CIRCUITS 



any control loop design, based on a mathematical analysis, should be 

 verified with actual equipment tests, and the approximate equations may 

 be used to give an extremely useful preliminary design even if the exact 

 mathematical description of the actual equipment is not known. 



8-34 STABILIZATION LOOP MECHANIZATION 



The type and size of the antenna actuators are chosen largely from the 

 search loop requirements; and to save space and weight, the same antenna 

 and actuators are used in the stabilization loop. However, the remaining 

 components in the loop are not identical; they are selected according to 

 type of configuration desired in Fig. 8-37. Actually each of the three 

 designs has different mechanization problems and a complete discussion 

 of the details is beyond the scope of this text. However, a few important 

 considerations, common to the designs, will be given. 



In Fig. 8-37a two rate gyros provide electrical signals proportional to 

 antenna space rates about the azimuth and elevation gimbals. The signal 

 from each gyro is compared with an azimuth and elevation reference voltage 

 from a track loop amplifier, and the resulting difference voltage (passed 

 through appropriate compensating networks) is then used to move the 

 antenna in its channel through a power amplifier and actuator. Usually 

 the same power amplifiers serve the search loop and the stabilization loop, 

 but the compensating networks are different and relays convert the search 

 loops to stabilization loops. To prevent transients during this brief tran- 

 sition period, it is often necessary to short-circuit the capacitors in the 

 compensating networks. The rate gyro is a self-contained unit obtainable 

 in various sizes and with various degrees of accuracy. It is important that 

 the rate gyros have low threshold voltages and a dynamic range large 

 enough to measure the highest space rates due to vibration, antenna 

 unbalance, and aircraft motion expected in normal operation. The gyros 

 are mounted securely on the antenna after being carefully aligned; but 

 although they are on the antenna during the search mode, they are not 

 usually used to provide space rate stabilization in the search mode. As 

 discussed in Paragraph 8-27, search stabilization must be derived from a 

 space position reference. Therefore, the dynamic range of the gyros need 

 not be so large as to measure the higher velocities that occur during the 

 search loop transients. On the other hand, the gyros must be sturdy enough 

 to withstand the extra forces that occur incident to rapid changes in 

 direction of motion. Integrating rate gyros such as the HIG gyros with 

 gimbals floating in highly viscous fluid provide considerable damping, and 

 the problem is not as serious as it is with gyros for which damping is 

 provided only by electrical feedback loops. This is a necessary considera- 

 tion also in configuration (b); it is not important in configuration (c) 



