Variables, 14 controlling

Like other thermoplastics, they exhibit melt fracture (32) above certain critical shear rates. In extmsion, many variables control product quaUty and performance (33). 

Analog alarms can be defined on measured variables, calculated variables, controller outputs, and the like. For analog alarms, the following possibilities exist ... 

When solution must be pumped, consideration should be given to use of holding tanks between the dry feed system and feed pumps, and the solution water supply should be controlled to prevent excessive dilution. The dry feeders may be started and stopped by tank level probes. Variable-control metering pumps can then transfer the alum stock solution to the point of application without further dilution. Means should be provided for calibration of the chemical feeders. Volumetric feeders may be mounted on platform scales. Belt feeders should include a sample chute and box to catch samples for checking actual delivery with set delivery. Gravimetric feeders are usually furnished with totalizers only. Remote instrumentation is frequently used with gravimetric equipment, but seldom used with volumetric equipment. 

Rapid and complete mixing of chemicals, feedwater and slurry solids must be provided. This should be comparable to conventional flash mixing capability and should provide for variable control, usually by adjustment of recirculator speed. 

With a host computer allows moving on to advanced control and multi-variable control. The unit is sensitive to day/night temperature swings and the multi-variable control can track ambient changes. 

The variables that control the extent of a chromatographic separation are conveniently divided into kinetic and thermodynamic factors. The thermodynamic variables control relative retention and are embodied in the selectivity factor in the resolution equation. For any optimization strategy the selectivity factor should be maximized (see section 1.6). Since this depends on an understandino of the appropriate retention mechanism further discussion. .Jll be deferred to the appropriate sections of Chapters 2 and 4. 

Chemical equilibria being of a dynamic type, equilibrium states are altered by changes in the variables controlling them. The effect of such changes can be interpreted qualitatively on the basis of a principle which was enunciated independently by Le Chatelier in 1885 and by Braun one year later. It states that when a system in a state of dynamic equilibrium is subjected to a stress imposed by variation in anyone of the variables controlling the equilibrium state, the system will tend to adjust itself in such a way as to minimize the effect of the stress. The variables of interest in this connection are temperature of the system, pressure on the system, and concentrations for the reactants and products taken individually. 

What process variables control the degree of orientation in a film manufactured via cast film extrusion and blown film extrusion ... 

In the MBR, the applicator of plate steel was an important safety feature in the possible event of vessel rupture or explosion. Temperature and pressure measurements, stirring, infinitely variable control of microwave power input, the cold-finger, as well as a pressure relief valve, have all contributed significantly to the safety and reliability of the system. 

Arnorsson, S., E. Gunnlaugsson and H. Svavarsson, 1983, The chemistry of geothermal waters in Iceland, II. Mineral equilibria and independent variables controlling water compositions. Geochimica et Cosmochimica Acta 47, 547-566. 

Process parameters of primary importance include roll speed, differential roll speed, roll gap, metal flow rate, metal stream velocity, and melt superheat. The mass median diameter of particles diminishes exponentially as the roll speed increases. It is possible to obtain a smaller mass median diameter when one of the rolls is kept stationary rather than rotating the two rolls at the same speed. Metal flow rate seems to have a negligible effect on the mass median diameter. However, the mass median diameter increases with increasing metal stream velocity, suggesting that the relative velocity of the metal stream to the periphery of the rolls may be a fundamental variable controlling the mass median diameter. The size distribution is approximately constant for the conditions studied. 

The data tend to be imprecisely gathered (often because researchers are unsure of what they are looking for), and therefore possess extreme within-group variability. Control and historical data are not used to adjust for variability or modify test performance. 

Put this solution in a cuvette and then insert it in a colorimeter previously warmed up to 25 °C. Set the wavelength at 340 nm. Carefully adjust the absorbance of this solution to 0.1 by making use of the proper variable control as explained earlier,... 

Example 1.5. For a binary distillation column (see Fig. 1.6), load disturbance variables might include feed flow rate and feed composition. Reflux, steam, cooling water, distillate, and bottoms flow rates might be the manipulated variables. Controlled variables might be distillate product composition, bottoms product composition, column pressure, base liquid level, and reflux drum liquid level. The uncontrolled variables would include the compositions and temperatures on aU the trays. Note that one physical stream may be considered to contain many variables ... 

A host of gadgets and software are available to perform a variety of computations and logical operations with control signals. For example, adders, multipliers, dividers, low selectors, high selectors, high limiters, low limiters, and square-root extractors can all be implemented in both analog and computer systems. They are widely used in ratio control, in computed variable control, in feedforward control, and in override control. These will be discussed in the next chapter. 

The system is really unstable in the classic linear sense. The nonlinear bounds or constraints on the manipulated variable (control-valve position) keep it in a limit cycle."... 

Computed variable control, (a) Maas flow rate (b) heat input (c) composition (piessure-compcnBated temperature). 

In the cat reforming process, two important variables control toluene make the composition of the feed and the operating conditions in the reactors. As to the first, some compounds are more suitable for reforming into... 

Adams, R. J., J. M. Buffergton, A. G. Sparks, and S. S. Banda. 1994. Robust multi-variable control, advances in industrial control. London Springer-Verlag. 

Quantity Measured Variable Controlled Name of method... 

The ITL4 variable controls how many times the step size can be reduced during a simulation. The default value is 10, so after the step size has been reduced 10 times the simulation will stop. If the value of the option is not set to 100 then change the value to 100. 

Structural Variables Controlling the Mechanical Properties of Thermoplastics... 

Known Variables — Controllable In any experimental situation, cettain conditions are held constant during the course of the experiment. A batch of copolymer may be made with a measured quantity of catalyst, at a given reaction temperature, and reacted for a certain definite time. The vessel is free of water, die monomers are charged in a definite proportion, and any other conditions that may affect the result are held fixed. The next portion of the experiment may involve one of these conditions controlled at a new level while the others remain fixed. Proper design of experimental programmes presupposes ability to control the important factors so that the variation due to these factors can be calculated. In Chapter VI, experimental designs for various situations are coveted. 

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