Servo system

During the thickness measurement, the steel strip is hot (1500° to 1750°F), moving (about 2000 feet per minute horizontally with possible vertical vibrations up to. several inches in amplitude), and subjected to a spray of cooling water. The measurement is accomplished through a servo system, shown schematically in Figure 3-1. 

The top and the bottom x-ray detector each contain a multiplier phototube coated with phosphor. This tube compares the intensity of the x-ray beam entering the detector with that of the light from the reference standard, a discharge lamp. The reference beam is part of a circuit that maintains the x-ray source at constant intensity. The deviation wedge comes to rest when the intensities of the transmitted x-ray beams stand in a predetermined ratio. At this point, the unbalance in the servo system has been compensated, and the position of the deviation wedge consequently indicates the thickness of the strip. In 1955, this application was made fully automatic that is, the unbalance (or error signal) just mentioned was used to readjust tandem cold reduction mills of the United States Steel Corporation. Automatic control proved significantly more effective than manual control. 

In our examples, we will take Gm = Ga = 1, and use a servo system with L = 0 to highlight the basic ideas. The algebra tends to be more tractable in this simplified unity feedback system with only Gc and Gp (Fig. 5.6), and the closed-loop transfer function is... 

With a proportional controller, Gc = Kc, the transfer function of this closed-loop servo system is... 

Figure 10.12. Block diagram of a 2 x 2 servo system. The pairing of the manipulated and controlled variables is not necessarily the same as shown in Fig. 10.11.

Figure M5.3. A sample negative feedback closed-loop generated within Simulink. This servo system has a first order process function and uses a PID controller. The output is sent to a graphing tool for plotting.

In subprograms for operating scanning devices, the primary algorithm may include a do and wait operation (for a stepper motor) or a do and look operation (for a servo system). Try to avoid problems that could arise if you move your software to a faster, newer PC. With a new PC running at a faster clock speed than an old one, the faster do operation will require a longer wait if the scanner operation is matched to the duration of do + wait. Thus, the CAM should be treated as three separate units the microscope, the interface, and the PC. The PC will become obsolete before the microscope. 

Potentiometer A component of a servo system which measures and controls electrical potential. 

No single set of electrical and physical requirements can be stated for servomechanisms intended for these diverse military applications. The characteristics of each servomechanism are determined by the function it is to perform, by the characteristics of the other devices and equipments with which it is associated, and by the environment to which it is subjected. It will often be found that two or more servo-system configurations will meet a given set of performance specifications. Final choice of a system may then be determined by such factors as ability of the system to meet environmental specifications, availability of components, simplicity, reliability, ease of maintenance, ease of manufacture, and cost... 

Hydraulic Servo-systems Mohieddine Mali and Andreas Kroll... 

Hard Disk Drive Servo Systems (2nd Ed.) Ben M. Chen, Tong H. Lee, Kemao Peng and Venkatakrishnan Venkataramanan... 

The rms linewidth of the dye laser has so far been reduced to 300 Hz relative to a reference cavity with the help of an intracavity ADP phase modulator and a fast servo system which compensates for small rapid optical path fluctuations in the liquid dye jet [24]. A perhaps even more elegant alternative is the external laser frequency stabilizer [25] which compensates for phase and frequency noise after the light has left the laser cavity. J. Hall and coworkers [26] have recently reduced the linewidth of a commercial ring dye laser to sub-Hz levels with such a device. 

Simplified electromagnetic servo system for an electronic balance. 

A servo system is a device in which a smail eiectric signal causes a mechanical system to return to a nul position. 

Servo system A device in which a small eiror signal is amplified and used to return the system to a null position. 

Homeostasis. Anyone who tries to regulate a chemical reaction system by a multitude of valves or switches (Figure 5) soon becomes frustrated with the instability of his experimental system and appreciative of automatic control devices (servo systems). For example, for the external control of preselected pH and C02 activity, an automatic titrator (pH — stat) can be used to dose continuously and automatically the quantity of C02 which is necessary to maintain constant pH. Feedback is an essential feature of such a control system there are essentially two major components, a controlling system (error detector) and a controlled system (13) (Figure Id). 

In the computations, which were only of an illustrative nature, it was assumed for simplicity that fo(J.v) depends linearly on the irradiation power density J. Taking into consideration the more complex dependences of fo on J presents no llindamental difBculties and can be carried out of analytical approximations of the tabulated fo(J,v) characteristics for several different irradiation levels. The t (x) curve shows how the automatic tracking servo system vary the design parameters Ng and Ng in the course of the day. The calculated t (x) dependences and also the J(r) curve used in the computation are shown in Fig. 8. 

Figure 4.6 Mirror spacing during successive down- and up-frequency scans of the locked cavity-servo system. The mirror spacing was monitored by a capacitance micrometer, the output being displayed on the ordinate axis vs. time, with 2 min sweep period. The glitch deviation was 2.5 pm, caused by an absorbing sample of natural isotopomer 0 CS in OCS at 13 Pa (Reprinted from Rezgui et aV with permission from Elsevier Science)...

The cause of the glitch proved to be inherent in the performance of the servo system when locking to a cavity profile whose Q was reduced by a narrower... 

The servo feedback loop functions by reducing the amplitude of the FM superposed by the cavity response onto the MMW signal to as small a value as possible. This does not mean, however, that the MMW output becomes unmodulated. Rather, the original modulation is replaced by one at twice the modulation frequency, that goes undetected by the servo system s phase-coherent detector. It may, however, be observed and converted into DC by a second phase-coherent detector responding to twice the modulation frequency. In the system so far described, this DC voltage will correspond to the second derivative of the cavity frequency profile (Section 4.1) and will therefore take on a fixed value characteristic of the cavity-g and its coupling coefficient. 

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