From PID Controllers, 2nd Edition

In this section we illustrate how complex control systems can be built from simple components by using the paradigms we have discussed. The problem is quite complex. It involves selection of measured variables and control variables, and it requires significant physical understanding of the process.

The Process

The process to consider is a chemical reactor. A schematic diagram is shown in Figure 7.36. Two substances A and b are mixed in the reactor. They react to form a product. The reaction is exothermic, which means that it will generate heat. The heat is dissipated through water that is circulating in cooling pipes in the reactor. The reaction is very fast; equilibrium is achieved after a time that is much shorter than the residence time of the reactor. The flow qA of substance A is considerably larger than qB. Efficiency of the reaction and the heat generation is essentially proportional to the flow qB.

A static process model is useful in order to understand the control problem. Figure 7.37 shows the efficiency and the heat generation as a function of temperature. In the figure we have drawn a straight line that corresponds to the cooling power.

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© 1995 Instrument Society of America

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Motion controllers range from simple linear controllers to complex, user-programmable modules that act as controllers within complex integrated multi-axis motion systems.
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Temperature controllers accept inputs from temperature sensors or thermometers, and then output a control signal to keep the temperature at the desired level.
Flow Controllers
Flow controllers monitor and maintain flow-rate variables, typically in process applications.
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Universal process controllers constitute a broad area of control devices that may be employed in the monitoring and control of many different process variables, including temperature, pressure, flow and other values.
Level Controllers
Level controllers monitor, regulate, and control liquid or solid levels in a process.

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