Servo control

If the acceleration is variable, as in sinusoidal movement, piezoelectric systems are ideal. In case of a constant acceleration, and hence a force that is also constant, strain gages may be employed. For petroleum applications in boreholes, however, it is better to use servo-controlled accelerometers. Reverse pendular accelerometers and single-axis accelerometers are available. 

Figure 4-219 shows the schematic diagram of a servo-controlled inverted pendular dual-axis accelerometer. A pendulum mounted on a flexible suspension can oscillate in the direction of the arrows. Its position is identified by two detectors acting on feedback windings used to keep the pendulum in the median position. The current required to achieve this is proportional to the force ma, and hence to a. ... 

Figure 4-220 shows the schematic diagram of a servo-controlled single-axis accelerometer. The pendulum is a disk kept in position as in the case of the reverse pendulum. Extremely efficient accelerometers can be built according to this principle in a very limited space. The Sunstrand accelerometer is seen in Figure 4-221. 

Figure 4-219. Sketch of principle of a servo-controlled inverted pendular dual-axis accelerometer.

Figure 4-220. Schematic diagram of a servo-controlled single-axis accelerometer.

Figure 4-221. Servo-controlled single-axis Sunstrand accelerometer (a) accelerometer photograph (b) exploded view of the accelerometer. (Courtesy Sunstrand [102].)...

Figure 9.5 shows a main servo controlled by two thermostatic pilots sensing load temperature (type CVT) and a solenoid valve (type EMV). Any of these pilots may be used separately with the servo valve. 

Figure 11. Principle of servo control system for optical paths stabilization in a fibre linked interferometer.

When we change a specific operating condition, meaning the set point, we would like, for example, the pH of the bioreactor to follow our command. This is what we call servo control. 

Example 5.7 We have to design a servo-controller for a mixing system. A blue dye for making denim is injected into a stream of water. The injected dye is blended into the pipe flow with the aid of in situ static mixers. A photodetector downstream is used to monitor the dye concentration. The analog output of the detector is... 

The simulations involve the solution of the rigorous tray-by-tray model of each sequence, given by equations 1 to 6, together with the standard equations for the PI controllers for each control loop (with the parameters obtained through the minimization of the lAE criterion). The objective of the simulations is to And out how the dynamic behavior of the systems compare under feedback control mode. To carry out the closed-loop analysis, two types of cases were considered i) servo control, in which a step change was induced in the set point for each product composition under SISO feedback control. 

In another elongational rheometer (221), the specimen is suspended on the end of a flexible tape, which is wound onto a wheel turned by a servo-controlled torque motor. This design is the basis for the Gottfert Rheostrain instrument, with which strain rates of 5 x 10 3 to 2 s-1 are possible. 

Normally the guidance includes sensing, computing, directing, stabilizing and servo-control components... 

The light generator is servo-controlled by the DSC software, which permits a choice of both light intensity and duration of the irradiation. The source can be filtered by sapphire disks in order to cut off wavelengths lower than 300 nm and thus to be representative of outdoor aging conditions. 

Positioning systems can use either an open-loop or a closed-loop control system. In closed-loop motion control, such as the optimized positioning of solar collectors based on measuring their shadows, the positions of both the collector and the shadow are continuously detected. Based on this feedback, the position and velocity of the collector can both be controlled. The reported position is continuously compared to the desired one, and the collector is moved to reduce the error between the two. This is called servo control (Figure 3.154). 

Figure 1 Apparatus of Oxford experiment [6]. LI, L2 tunable dye lasers. UV ultra violet radiation (243 nm). RF radiofrequency dissociation of flowing molecular hydrogen. PI signal photomultiplier (Lyman-a detector). P2 photomultiplier for cavity locking and signal normalisation. SI cavity length servo-control. C conrouter. AOM acousto-optic modulator. T heated quartz cell containing tellurium. S2 laser frequency servo-control. D fast photodiode...

FIG. 15.23 Extensional rheometer, designed by Miinstedt (1979). A servo control system is used to maintain a specified extensional rate of strain or a specified tensile stress. Courtesy Society of Rheology. For a modern version, see Miinstedt et al., 1998. 

Fig.1 Mechanical resonances of a 4-pL rotor filled with a specially shaped solid, simulating cylindrical and conical asymmetry Rotation speed was slowly increased by servo-controlled drive pressure. Cylindrical imbalance (long dash) enables corresponding modes of resonance to be identified. The ratio of jerk positions closely corresponds to the theoretical ratio of two different resonance modes. Higher bearing pressure increases the force constant and the frequencies of the mechanical resonances...

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