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Process capacity and dead time

Prior to attempting this workshop, you should review Chapter 3 in the book. [Pg.275]

This workshop will illustrate the effect on the process response of the three key process dynamic parameters process gain, process time constant and process dead time. You will also explore the impact that capacitance or Tag has on these process parameters. [Pg.275]

1 Process gain is the key process parameter affecting the extent (magnitude) of the response of a process or process element. [Pg.275]

3 The time constant is the key dynamic parameter that determines the ability of a process to reject, or attenuate, disturbances. [Pg.275]


WORKSHOP 3 PROCESS CAPACITY AND DEAD TIME Table W3.2 Attenuation for level at 5 per cent... [Pg.279]

Workshop 5 Controller tuning for capacity and dead time processes... [Pg.291]

From Fig. 2.2 it can be seen that the interacting multicapacity process differs from the dead time plus single-capacity process in the smooth upturn at the beginning of the step response. This curvature indicates that the dead time is not pure, but instead is the result of many small lags, and therefore the process will be somewhat easier to control. By the same token, derivative action will be of more value than it was in the case of dead time and a single capacity. Nonetheless, if we choose to estimate the necessary controller settings on the basis of a single-capacity plus dead-time representation we will err on the safe side. [Pg.42]

Because all the heat leaving the reactor flows through the walls and into the coolant, the capacities of reactants, walls, and coolant interact. But in view of the slight heat capacity of the bulb, its time constant does not significantly interact with the others. Basically the process is four-capacity plus dead-time. [Pg.75]

Again, processes do not fall into such neat classifications as two-capacity or single-capacity plus dead-time. The bulk of difficult processes lie between these limits. But the same control function described by Fig. 5.16 and Eq. (5.10) can be adjusted to accommodate dead time in addition to two capacities. Equation (5.11) indicates the required settings for optimal switching ... [Pg.141]

Make step changes in the steam rate for three different tank level set points of 5, 50, and 95 per cent. Calculate the gain, time constant, and dead time for the three different process capacities. Present your results in Table W3.1 and then plot the time constant and gain in Figure W3.3. [Pg.277]

Figure 6.2. Illustration of fitting Eq. (6-2, solid curve) to open-loop step test data representative of self-regulating and multi-capacity processes (dotted curve). The time constant estimation shown here is based on the initial slope and a visual estimation of dead time. The Ziegler-Nichols tuning relation (Table 6.1) also uses the slope through the inflection point of the data (not shown). Alternative estimation methods are provided on our Web Support. Figure 6.2. Illustration of fitting Eq. (6-2, solid curve) to open-loop step test data representative of self-regulating and multi-capacity processes (dotted curve). The time constant estimation shown here is based on the initial slope and a visual estimation of dead time. The Ziegler-Nichols tuning relation (Table 6.1) also uses the slope through the inflection point of the data (not shown). Alternative estimation methods are provided on our Web Support.
The first order function with dead time is only appropriate for self-regulating and multi-capacity processes. In other controller design methods, we should choose different functions to fit the open-... [Pg.106]

On increasing the adsorption temperature, shorter dead-times are observed in Fig. 35 (respectively 280, 220, 190 and 140 s for rads = 50, 100, 150 and 200°C) thus the amount of NH3 adsorbed onto the catalyst surface is reduced, in line with the exothermic NH3 adsorption process. Likewise the TPD runs, whose areas decrease on increasing the adsorption temperature, also confirm the lower storage capacity of the system at higher temperatures. [Pg.169]

Postulate a model. In Example 12.1 we observed that a jacketed cooler is a multicapacity process. For our problem we can identify the following three interacting capacities in series (1) heat capacity of tank s content, (2) heat capacity of the coolant in the jacket, and (3) heat capacity of the tank s wall. Therefore, our first suggestion is to use a third-order overdamped model without significant dead time. A closer examination of the physical system reveals that the tank s wall does not possess significant capacity for heat storage and could be omitted. Consequently, we suggest a second-order model without dead time of the form... [Pg.696]

Another important factor must be brought out. By definition of the primary and secondary capacities, t2 is never greater than n, regardless of their relative positions in the loop. This means that the most difficult two-capacity process will be one where n/n = 1.0. For J. -ampIitude damping, P would be 16 percent. By comparison, the dead-time process is 20. g or 12.5 times more difficult to control than the most difficult two-capacity process. [Pg.29]

Between the most and least difficult elements lies a broad spectrum of moderately difficult processes. Although most of these processes are dynamically complex, their behavior can be modeled, to a large extent, by a combination of dead time plus single capacity. The proportional band required to critically damp a single-capacity process is zero. For a dead-time process. It Is Infinite. It would appear, then, that the proportional band requirement Is related to the dead time in a process, divided by Its time constant. Any proportional band, hence any process, would fit somewhere In this spectrum of processes. A discussion of multicapacity processes In Chap. 2 will reaffirm this point. [Pg.31]

It is interesting to note the comparison between the controllability of this process and the two-capacity process. Taken on the basis of an equal ratio of secondary to primary element, the dead-time plus capacity process is TOO/ttIO or 8 times as difficult to control. Recall that the pure dead-time process was 12.5 times as difficult to control as the most difficult two-capacity process. [Pg.33]

As pointed out in Chap. 1, it is doubtful whether any real process consists exclusively of dead time or single capacity or even a combination of the two. But having become familiar with the properties of these elements, we now can proceed to identily their contributions to complex processes. Some processes are difficult to control-particularly where dead time is dominant. But many processes are poorly controlled because their needs are not understood and therefore not satisfied. [Pg.37]

Anyone who has tried to control composition in a stirred tank knows that it is not a single-capacity process. It would only be single-capacity if the contents of the vessel were perfectly mixed. But no mixer can move material from the inlet pipe to the exit pipe in zero time-it is impossible. Consequently some dead time must exist, i.e., that time required for the agitator to transport a particle of fluid from inlet to outlet. The presence of any dead time changes the control situation entirely, for now the process is capable of oscillating in a closed loop, which places a limitation on both controller gain and speed of response. [Pg.81]

Figure 1.26 shows the required proportional band for j i-amplitude damping for any combination of dead time and capacity. A band of 100 percent (proportional gain of 1.0) is seen to be required for a process whose Td/ri = 1.2. But with (mmplomentary feedback, the same proportional gain could produce criti( al damping. Complementary feedback is, by this token, of advantage in the most difficult processes. [Pg.105]

A single-capacity process can tolerate zero proportional band and zero reset time. Compared to a dead time process, it can be concluded that the easier the process is to control, the less critical are its mode adjustments. [Pg.107]

The example that has been employed is a more severe test than would ever be encountered in a plant. Pure dead time is the most difficult process to control, and it is best compensated by an equal sample interval. Processes dominated by capacity are better controlled continuously if sampled, the interval should be as short as practicable. Then the uncer tainty in load response will be small because the sampling interval is small with respect to total response time. [Pg.117]

Both of these processes have similar characteristics, in that they are typically comprised of one large and many small capacities, i.e. valve actuator, transmitter, etc. The net result is a response indicative of a process with a dominant capacitance plus a dead time. Both of the above categories will be investigated and their specific differences and similarities will be identified. [Pg.163]

Recognize the open-loop response of capacity-dominated processes, with and without dead time. [Pg.271]

Feedback control is easiest and most successful for low-capacity processes without dead time. [Pg.283]


See other pages where Process capacity and dead time is mentioned: [Pg.275]    [Pg.276]    [Pg.277]    [Pg.278]    [Pg.280]    [Pg.281]    [Pg.275]    [Pg.276]    [Pg.277]    [Pg.278]    [Pg.280]    [Pg.281]    [Pg.41]    [Pg.43]    [Pg.129]    [Pg.90]    [Pg.16]    [Pg.160]    [Pg.16]    [Pg.6568]    [Pg.891]    [Pg.896]    [Pg.6567]    [Pg.886]    [Pg.32]    [Pg.107]    [Pg.299]    [Pg.67]    [Pg.44]    [Pg.70]    [Pg.153]   


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