Controller characteristics, desirable

After the type of system has been selected, many of these same factors must be considered in selecting the fluid for the system. This chapter is devoted to hydraulic fluids. Included in it are sections on the properties and characteristics desired of hydraulic fluids types of hydraulic fluids hazards and safety precautions for working with, handling, and disposing of hydraulic liquids types and control of contamination and sampling. 

Different procedures can be used in practice to activate the zeolite, and the choice of a particular method will depend on the catalytic characteristics desired. If the main objective is to prepare a very active cracking catalyst, then a considerable percentage of the sodium is exchanged by rare earth cations. On the other hand, if the main purpose is to obtain gasoline with a high RON, ultrastable Y zeolites (USY) with very low Na content are prepared. Then a small amount of rare earth cations is exchanged, but a controlled steam deactivation step has to be introduced in the activation procedure to obtain a controlled dealumination of the zeolite. This procedure achieves a high thermal and hydrothermal stability of the zeolite, provided that silicon is inserted in the vacancies left by extraction of A1 from the framework (1). The commercial catalysts so obtained have framework Si/Al ratios in the... 

Electrode geometry in controlled-potential electrolysis. When fast response and accuracy of potential control are desired, considerable attention must be paid to the design of the cell-potentiostat system, and several papers have discussed the critical parameters and made recommendations for optimum cell design.8"11 In general, to achieve stability and an optimum potentiostat rise time for a fast potential change, the total cell impedance should be as small as possible, and the uncompensated resistance should be adjusted to an optimum (nonzero) value that depends on the characteristics of the cell and potentiostat.9,12 The electrode geometry also should provide for a low-resistance reference electrode and a uniform current distribution over the surface of the... 

The goal of the above techniques is to achieve the following desirable controller characteristics ... 

Although unagitated tank crystallizers arc quite commonly used, they are greatly limited with respect to control of desired crystal product characteristics. The only variables are the initial and final temperatures and initial concentration, which determine the product yield. Rate of cooling may be controlled to some extent by the use of insulation or a tempered water jacket. The only liquor circulation which takes place is due to natural convection currents. As crystals grow and settle to the bottom of the vessel, agglomeration and occlusion of mother liquor may take place. Serious difficulties arise from the inability to control crystal product size and quality. 

One set of properties over which charcoal makers do have some control is the size and shape of the wood pieces loaded into the kiln. Many practical considerations affect the way wood pieces are cut and shaped before being put in the kiln. The first of these is the wood source. If waste wood from wood-processing industries is being used as a feedstock, then the size and shape of the wood pieces are largely predetermined. However, if the wood comes from plantations grown specifically to supply the kilns, there is greater scope for optimising size and shape characteristics. Desirable features include ... 

Product Amenable to Fabrication. (a) Products from PDPM may be available to a fabricator as either oxide, carbide, or metal. (b) Process controls may yield products with the characteristics desired for optimum fabricability. 

Modem chargers use fast acting and accurate electronic devices to control the desired output characteristics. The rectifying device can be diodes or thyristors. 

Another characteristic desirable in antiseptics used by healthcare professionals is that they act as microbiologically lethal agents. The spectmm of activity study does not allow evaluation of this characteristic since incubation exceeds 18 hours. However, the time-kill kinetic study does allow assessment of the rate of kill of an antiseptic provided certain variables are controlled [34]. 

Fast evaporation could cause hollowness and even fracture of the coating. For this reason factors affecting drying rate have to be controlled to prevent or moderate lack of uniformity of the coating depending on the characteristics desired for each product. 

Many processes require speed controls. Performance and reliabilities of these controls are very similar to those of the temperature controls—you get what you purchase. Early speed controllers, like the temperature controllers, were mechanical. Speeds were held within 5 percent, resulting in poor plastic melt control. Where better speed control is desired, the solution is the same as in temperature control only the equipment names are changed. A device is added to the motor, and an integral characteristic is provided, corresponding to the automatic reset with heat. It brings the speed closer to the set point. A derivative characteristic, corresponding to the rate in heat, ensures a prompt response to any upsets. 

Unfortunately, because self-condensation of silanols on the same silicone can occur readily, the controlled reaction of disilanol or trisilanol compounds with telechelic silanol polymers to form a three-dimensional network is not feasible. Instead, networks are derived from reactions of telechelic polymers with crosslinkers containing reactive groups such as alkoxysilanes, acyloxysilanes, silicon hydrides, or ketoximinosilanes, as in the reactions 24-27 (207). The choice of the cross-linking agent depends on the specific product characteristics desired. 

Other important operating parameters include plasticizer changes, gas type and pressure, gap length between spinneret and quench bath, line speed, and rope tension. All variables must be carefully controlled to obtain a hoUow fiber of desired characteristics. 

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