Control loops basic elements

What are the basic hardware components of a feedback control loop Identify the hardware elements present in a feedback loop for the temperature control of a stirred tank heater. 

A safety instrumented system, like a basic process control system, is also composed of sensors, controUer(s), and final elements. Although much of the hardware appears to be similar, safety instrumented systems and basic process control systems differ very much in function. The primary function of a control loop is generally to maintain a process variable within prescribed limits. A safety instrumented system monitors a process variable and initiates action when required. 

Process piants are composed of hundreds of control loops. These control loops are used to maintain pressure, temperature, flow, level, and analytical process variables. The basic elements of a control loop are ... 

Determine the An element of the relative gain array for each of the basic distillation control configurations (i.e. the LV, DV and LB configurations). Consider only the composition control loops so that the problem reduces to a 2 x 2 system. 

Some of the earliest work in multivariable control involved the use of decouplers to remove the interaction between the loops. Figure 16.7 gives the basic structure of the system. The decoupling matrix is chosen such that each loop does not affect the others. Figure 16.8 shows the details of a 2 x 2 system. The decoupling element Dy can be selected in a number of ways. One of the most straightforward is to set I>n = D22 = 1 and design the 0 2 and Dji elements so that they cancel... 

The basic controller in the feedback loop is designed for load disturbances Ui) A precompensator is used on the setpoint signal. This element is designed so that the response to setpoint changes, with the compensator in service, is the desired one. The precompensator is defined as I>ss(z) ... 

We will start by recalling the typical computer loop for direct digital control shown in Figure 26.5. For presentational purposes only we simplify the loop to that shown in Figure 27.8 by retaining its basic four components process, A/D converter with the associated sampler, digital controller, and D/A converter with the associated hold element. We... 

Fig. 2.8-19 Basic logical elements of open-loop control technology.

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