454 REGULATORY CIRCUITS 



are equivalent in a mathematical sense, but practically the arrangement of 

 the physical equipment is entirely different, and, depending on the appli- 

 cation, the mechanization can create discrepancies between the theoretical 

 and realized loop performance. In fact, in many control loops the mecha- 

 nization characteristics, which are incidental to the primary loop function, 

 may prevent the realization of a workable system. Therefore, it is necessary 

 to know as much as possible about equipment characteristics before a 

 design is finalized. Unfortunately, component characteristics vary widely 

 depending on the application, and it is impossible to discuss them in detail. 

 However, the general principles of operation are outlined below for three 

 different systems. 



Rate Gyro Stabilization Loop. The rate gyroscope^"* is a self- 

 contained unit which produces an electrical signal, usually a voltage, 

 proportional to a space rate about a particular axis. In the stabilization 

 loop design shown in Fig. 8-37a two rate gyros are used, one to measure 

 space rates about the elevation axis and the other to measure space rates 

 about the azimuth axis of the antenna. Both gyros are mounted on the 

 antenna dish^^ where the antenna space rates are measured directly. As 

 shown in the figure, the space rate {Atl) of the antenna tracking line 

 angle, Atl, is measured by gyro and converted to a voltage proportional 

 to Atl- This voltage is compared with an antenna rate command voltage 

 Vr and the voltage difference, the rate error Er, is used to control the 

 antenna actuators through appropriate amplifiers in a direction which will 

 reduce the rate error. 



Although only one channel is shown, two control loops are needed — one 

 for each antenna motion — and these loops are interconnected, not only 

 through the common space platform and antenna structure but through 

 the gyroscopes as well, because space accelerations in one channel influence 

 the gyro output voltage in the other channel to a degree which is determined 

 by the gyro characteristics and the gyro orientation. However, unless the 

 stabilization loop is of very large bandwidth, this effect can be made 

 negligible by selecting the proper gyro and by choosing the optimum gyro 

 axis mounting.^^ 



As shown in the figure, motion of the aircraft angle, Aa^ is also detected 

 by the gyro and converted to a voltage, essentially a rate error, which is 

 used to move the antenna at a rate in space opposite to the aircraft space 



34See Locke, Guidance, Chap. 9, pp. 350-353. 



^^Note that the effective azimuth gyro gain in volts per unit of velocity is proportional 

 to the cosine of the elevation angle and that it will change during normal operation. For 

 computational purposes this is often desired, but it may affect the stability of the azimuth 

 stabilization loop if the elevation angle becomes large. 



^A complete discussion of this problem is given in a paper, "Analysis of Gyro Orientation," 

 by Arthur Mayer in the Transactions of the Professional Group on Automatic Control, PGAC-6, 

 December 1958, p. 93. 



