Windup

Fig. 9. Extmsion coating A, unwinding of substrate B, pressure roU C, chill roU D, die E, stripper roU F, edge trimmer and G, windup of coated...

In earlier years, the windup speed was 275—375 mpm (m /min) with 0.5 kg of yam per bobbin. In the 1990s, winders are designed for 10—25-kg bobbins, two or more bobbins per winder, operating at speeds up to 6000 mpm, and equipped with automatic bobbin changers. 

Godets Traverse guide Doff position Windup floor... 

No coherent threadline could be maintained and the extmdate flew off the windup as short, brittle, crystalline lengths. Not until many years later did other workers show that this polymer on cooling exhibits a mesophase transition directly from the isotropic melt to a smectic A phase. Good sources of information on Hquid crystals and Hquid crystal polymers are available (212—216). 

The use of high or low limits for process variables is another type of selective control, called an override. The feature of anti-reset windup in feedback controllers is a type of override. Another example is a distillation column with lower and upper limits on the heat input to the column reboiler. The minimum level ensures that liquid will remain... 

Process-variable feedback for the controller is achieved by one of two methods. The process variable can (I) be measured and transmitted to the controller by using a separate measurement transmitter with a 0.2-I.0-bar (3-15-psi pneumatic output, or (2) be sensed directly by the controller, which contains the measurement sensor within its enclosure. Controllers with integral sensing elements are available that sense pressure, differential pressure, temperature, and level. Some controller designs have the set point adjustment knob in the controller, making set point adjustment a local and manual operation. Other types receive a set point from a remotely located pneumatic source, such as a manual air set regulator or another controller, to achieve set point adjustment. There are versions of the pneumatic controller that support the useful one-, two-, and three-mode combinations of proportional, integral, and derivative actions. Other options include auto/manual transfer stations, antireset windup circuitry, on/off control, and process-variable and set point indicators. 

By the very nature of batch processing, it is inevitable that process equipment will have idle time between batches. The idle time also could occur if the controller is not being used at all times during the execution of the batch (e.g., a flow controller may only be used during the feed of one of the reactants). During the idle time, control considerations such as reset windup must be considered to prevent the control signal from going outside of the control limits. 

A complete extrusion hne for the tire industry also consists of various downstream machinery, including the cooling hne which reduces the extrudate temperature from about 100°C-115°C at the head exit to ambient plus 5% at the windup stations or at the tread-cutting station. 

Seagall, N.L. Taylor, P.A. "Saturation of Single-Input Single-Output Controllers Written in Velocity Form Reset Windup Protection", lEC Process Des. Dev., 1986, 25., 495. 

This is the velocity form algorithm which is considered to be more attractive than the position form. The summation of error is not computed explicitly and thus the velocity form is not as susceptible to reset windup. 

Poly[5-(alkylamino)borazines] 7-10 exhibited suitable viscoelastic and thermal stabilities to be extruded in the molten state through the monohole spinneret of a lab-scale melt-spinning apparatus. Thus, an extruded filament (diameter, 200 gm) was drawn with a windup unit, that is, a graphite spool. This provided green fibers with a wide range of diameters (16 =s (f> =s 50 gm Table 2), depending on polymer architecture. 

Because of reset windup, this control mode is not well-suited for processes that are frequently shut down and started up. 

Reset windup is an inherent disadvantage of proportional plus reset controllers that are subject to large error signals. 

Proportional plus rate controllers are useful with processes which are frequently started up and shut down because it is not susceptible to reset windup. 

Corrosion/ Erosion Rates Windup, Materials of Construction... 

When a controller with integral action (PI or PID) sees an error signal for a long period of time, it integrates the error until it reaches a maximum (usually 100 percent of scale) or a minimum (usually 0 percent). This is called reset windup. 

A sustained error signal can occur for a number of reasons, but the use of override control is one major cause. If the main controller has integral action, it wfll windup when the override controller has control of the valve. And if the override controller is a PI controller, it will windup when the normal controller is setting the valve. So this reset windup problem must be recognized and solved. 

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