Discontinuous controller modes

Key words control algorithms, discontinuous control modes, continuous control modes, composite control modes, analog and digital processing, pH measurement and control, dyeing control. 

In this mode of eontrol, the eontroller appUes high power to the heater if the temperature is well below the setpoint, and the applied power decreases as the temperature approaehes the setpoint. Proportional control is also referred to as stepless control, since it avoids the sharp ehanges inherent in a discontinuous control mode. This mode of control can be represented as shown in Fig. 7.6. 

This chapter considers a simple boost converter often used in power electronic systems. Figure 8.1 depicts its circuit schematic. In this circuit, the MOSFET transistor and the diode may be considered non-ideal switches. The transistor is a controlled power switch. Boost converters are designed that they operate either in so-called continuous conduction mode or in discontinuous conduction mode. In continuous conduction mode the inductor current never falls to zero. Accordingly, the converter assumes two states per switching cycle. When the transistor is on, the diode is off and vice versa. The diode commutates autonomously and oppositely to the transistor. Hence, there are two system modes in a healthy boost converter. 

These control methods can be used in aU of the PWM converter configurations. The converters can operate in either continuous current mode (CCM) or discontinuous current mode (DCM). If the current through the output inductor (e.g., refer to the circuit shown in Fig. 10.80(a)) never reaches zero, then the converter operates in CCM, otherwise DCM occurs. 

The operation of a discontinuous-mode, flyback converter is quite different from that of a forward-mode converter, and likewise their control-to-output characteristics are very different. The topologies that fall into this category of control-to-output characteristics are the boost, buck/boost, and the flyback. The forward and flyback-mode converters operating under current-mode control also fall into this category. Only their dc value is determined differently. Their representative circuit diagram is given in Figure B-12. 

The use of stirred fermenters with automatic control of the culture environment is the most suitable technique to evaluate bacterial or fungal kinetics. Cultures can be operated in discontinuous mode (batch cultures). 

It is possible to vary the load or, in hard machines, the displacement, either in ramp mode or with a discontinuous increment (step mode). The ramp function needs to be smooth, as well as linear, and there is evidence (Mayo Nix, 1988) that if the ramp is digitally controlled, the data will vary for the same mean loading rate according to the size of the digitally produced load increments, unless these are very small. 

Yasaee M, Bond LP, Trask RS, Greenhalgh ES. Mode II interfacial toughening through discontinuous interleaves for damage suppression and control. Compos Part A Appl Sci Manuf 2012 43 121-8. http //dx.doi.Org/10.1016/j.compositesa.2011.09.026. 

The fermentations were carried out in stirred tank reactors with 10 L woiidng volume in discontinuous fed-batch mode which means that carbon and nitrogen sources were fed to the media in several portions but not continuously. The temperature was maintained at 30 C. The pH was regulated automatically to maintain 7 0.1 by addition of 20 wt% NaOH and 20 wt% H3PO4 respectively. Agitation and aeration were controlled manually. 

Strength, unlike elastic modulus, is not even theoretically a readily determinable quantity. Overall elastic-plastic deformation in a structural adhesive might be describable in terms of intermolecular forces and models of viscous flow, but not at the discontinuous moment of fracture. In fact overall behaviour loses sight of the fact that it is normally isolated phenomena that control the magnitude of joint strength and the locus of failure (see Stress distribution mode of failure). The term isolated phenomena refers to voids, cracks, second phase material, and so on, which can act as stress concentrators. Clearly, it would be unwise to suggest that an adhesive bond tester should merely locate and size voids and cracks, as whether or not such a defect is active depends upon where it lies in the working stress pattern of the structure. 

Rock is the main material in a rock slope, and failure is controlled by the condition and orientations of discontinuities. Rock fall, wedge failure, and plane failure are typical modes of failure. 

Figure 3 Fermentation modes for recombinant bacteria, yeast, and animal cells. On the left-hand side, the feed streams and harvesting streams are schematically shown for the batch, fed-batch, and continuous cultivation of microorganisms. On the right-hand side, the product concentration and the cell density are shown. For batch and fed-batch a discontinuous product concentration profile is obtained. With constitutive expression of a product, the product concentration is dependent on the cell density. Product is present in the culture supernatant during the whole production cycle and thus more susceptible to degradation. When the product formation is induction controlled, the production concentration raises sharply after addition of the inductor. The residence time of the product in the bioreactor is reduced. For continuous culture a constant product concentration profile is maintained over the entire production cycle. The residence time of the product in the bioreactor depends on the harvesting time and is shortest tor all fermentation modes when harvesting is continuously performed. Changing the mode of production can highly influence the composition of feed for preparative chromatography.

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