Typical control systems

Decide on the type of control instrument that will be used, including whether it will be a local instrument or tied into the plant computer control system. Also decide on the type of actuator that can be used, the signal system, and whether the instrument will record data. This step should be done in conjunction with steps 1 to 4. 

Decide on the alarms and interlocks needed this would be done in conjunction with step 3 (see Chapter 9). 

In step 1 it is important to remember the following basic rules of process control  

Some simple examples of control schemes for common unit operations are given in the next section. 

Flow control is usually associated with inventory control in a storage tank or other equipment. There must he a reservoir to take up the changes in flow rate. 

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The gas turbine is a complex system. A typical control system with hierarchic levels of automation is shown in Figure 19-3. The control system at the plant level consists of a D-CS system, which in many new installations is connected to a condition monitoring system and an optimization system. The D-CS system is what is considered to be a plant level system and is connected to the three machine level systems. It can, in some cases, also be connected to functional level systems such as lubrication systems and fuel handling systems. In those cases, it would give a signal of readiness from those systems to the machine level systems. The condition monitoring system... 

Efficient use of electric motors requires appropriate control systems. Typical control systems for AC and DC electric motor operations are now discussed [ 10]. 

In this subsection, the reader is introduced to a number of the more typical control system configurations (briefly discussed earlier for a specific example). 

Figure 11 Screen of a typical control system for a single-pot processor. (Courtesy of Collette NV, Belgium.)...

Fig. 4.44 Failure possibilities in a typical control system with return feedback e.g. close loop control...

Figure 9.3 shows the typical control system development routes in which hardware and software requirements flow from the SIS architecture decisions. We see that application software requirements are to be defined in the knowledge of the selected embedded software. In other words you cannot specify the details of your application without knowing the operating systems and utility tools you are going to work with. 

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