Process attributes capacitance and dead time

All controllers, whether implemented as stand alone or as part of a distributed control system (DCS) application, have a switch which will allow either direct or reverse action. In general, the action of the controller is the last to be specified, since there is typically little choice in the action of the other elements in the loop. Once the other elements actions are known, the controller action may be set such that the overall loop action is reverse acting, or I/D. 

As we will see later in this chapter and elsewhere, the equations that govern the dynamics of some of the unit operations in typical process plants can be quite complex. Despite 

3 FUNDAMENTALS OF SINGLE INPUT-SINGLE OUTPUT SYSTEMS 

In this example the process consists of an oven which is storing heat to maintain a particular temperature T. The gas flow creates a flow of energy in Q. 2out is the flow of energy to the ambient or, in other words, the heat loss to the ambient. For an increase or decrease in the valve position changing the gas flow in, the temperature would 

The rate of change of volume in the tank can be written as a lumped parameter model, where all the resistance to flow is assumed to be associated with the valve, and all the capacitance of the process is assumed to be associated with the tank. This model is shown in Equations 3.1 and 3.2. The basis of Equation 3.1 is the principle of conservation, mass balance in this case (i.e. what goes in must come out or get accumulated in the system). 

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