Loop transfer system

Topical application Kiss-roll Loop transfer system Engraved roll Nip padding system Spray system Foam application... 

Another version of finish apphcation with transfer rolls is the loop transfer system, Fig. 2.5.A loop of fabric is immersed in finish liquid and then squeezed with the fabric to be treated between squeeze rollers. The finish is transferred to the fabric at a much lower wet pickup than possible by direct immersion. These roll transfer techniques are especially useful for the backside application of finishes, for example hand builders and flame retardants, to pile fabrics (without crushing the pile). 

The elements of a closed-loop control system are represented in block diagram form using the transfer function approach. The general form of such a system is shown in Figure 4.1. 

Fig. 4.1 Block diagram of a closed-loop control system. R s) = Laplace transform of reference input r(t) C(s) = Laplace transform of controlled output c(t) B s) = Primary feedback signal, of value H(s)C(s) E s) = Actuating or error signal, of value R s) - B s), G s) = Product of all transfer functions along the forward path H s) = Product of all transfer functions along the feedback path G s)H s) = Open-loop transfer function = summing point symbol, used to denote algebraic summation = Signal take-off point Direction of information flow.

A control system may have several feedback control loops. For example, with a ship autopilot, the rudder-angle control loop is termed the minor loop, whereas the heading control loop is referred to as the major loop. When analysing multiple loop systems, the minor loops are considered first, until the system is reduced to a single overall closed-loop transfer function. 

Find the closed-loop transfer function for the system shown in Figure 4.2. 

The system element dynamic equations can now be combined in the block diagram shown in Figure 4.31. Using equation (4.4), the inner-loop transfer function is... 

Assuming that the temperature of the surroundings O it) remains constant, the closed-loop transfer function (using equation (4.130)) for the temperature control system, is... 

Find an expression for the elosed-loop transfer funetion relating 6[ s) and 6a s) for the angular positional eontrol system shown in Figure 4.41. 

The elosed-loop transfer funetion for a eontrol system is given by equation (4.4)... 

In general, the eharaeteristie equation is most easily formed by equating the denominator of the transfer funetion to zero. Henee, from equation (5.23), the eharaeteristie equation for a elosed-loop eontrol system is... 

The closed-loop transfer function for any feedback control system may be written in the factored form given in equation (5.41)... 

The position of the closed-loop poles in the. v-plane determine the nature of the transient behaviour of the system as can be seen in Figure 5.5. Also, the open-loop transfer function may be expressed as... 

A eontrol system has the following open-loop transfer funetion... 

The open-loop transfer function for a control system is... 

A control system has the open-loop transfer function given in Example 5.8, i.e. 

Find the value of the open-loop gain eonstant K to make the eontrol system, whose open-loop transfer funetion is given below, just unstable. 

Closed-loop control systems are classified according to the number of pure integrations in the open-loop transfer function. If... 

A closed-loop control system has a nominal forward-path transfer function equal to that given in Example 6.4, i.e. 

Since H =, the system has unity feedback, and the closed-loop transfer function and step response is given by... 

Note that the eommand cloop works with both eontinuous and diserete systems. Running examp74.m will produee a step response plot of the elosed-loop diserete system, and the open and elosed-loop pulse transfer funetions will be written in the eommand window... 

Evaluation of loop-test results Although the thermal loop test approximates to the conditions which obtain in a dynamic heat-transfer system, in evaluating the results it is necessary to be aware of those aspects in which the test differs from the full-scale unit, as otherwise unwarranted confidence may be placed in the data. Assuming that adequate attention has been paid to the purity and condition of components, etc., the following factors will, according to ASTM G68 1980, influence the observed corrosion behaviour ... 

The operational duties of these smaller boiler systems vary widely, and for HW closed-loop heating systems, where the boiler is periodically offline, or in indirect heating systems where pipework, valves, or final heating units are exposed to chilly winds or icy conditions, some boiler winterization may be necessary. This is usually provided by replacing some of the water with glycols or other heat transfer fluids. 

Recycling of partially reacted feed streams is usually carried out after the product is separated and recovered. Unreacted feedstock can be separated and recycled to (ultimate) extinction. Figure 4.2 shows a different situation. It is a loop reactor where some of the reaction mass is returned to the inlet without separation. Internal recycle exists in every stirred tank reactor. An external recycle loop as shown in Figure 4.2 is less common, but is used, particularly in large plants where a conventional stirred tank would have heat transfer limitations. The net throughput for the system is Q = but an amount q is recycled back to the reactor inlet so that the flow through the reactor is Qin + q- Performance of this loop reactor system depends on the recycle ratio qlQin and on the type of reactor that is in the loop. Fast external recycle has... 

Example 2.14. Derive the closed-loop transfer function C/R and C/L for the system as shown in Fig. E2.14. 

We first establish the closed-loop transfer functions of a fairly general SISO system. After that, we ll walk through the diagram block by block to gather the thoughts that we must have in synthesizing and designing a control system. An important detail is the units of the physical properties. 

In this section, we will derive the closed-loop transfer functions for a few simple cases. The scope is limited by how much sense we can make out of the algebra. Nevertheless, the steps that we go through are necessary to learn how to set up problems properly. The analysis also helps us to better understand why a system may have a faster response, why a system may become underdamped, and when there is an offset. When the algebra is clean enough, we can also make observations as to how controller settings may affect the closed-loop system response. The results generally reaffirm the qualitative statements that we ve made concerning the characteristics of different controllers. 

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... 

Example 5.1 Derive the closed-loop transfer function of a system with proportional control and a first order process. What is the value of the controlled variable at steady state after a unit step change in set point ... 

Example 5.4 Derive the closed-loop transfer function of a system with proportional-derivative control and a first order process. 

The closed-loop system remains first order and the function is that of a lead-lag element. We can rewrite the closed-loop transfer function as... 

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