Direct Digital Control: Developments in digital electronics have led to many industrial processes being computer controlled. The first system used was Direct Digital Control (DDC), in which a computer measured each variable in the process, these signals being used to maintain the required set points in the process. As digital electronics developed, minicomputers become more […]
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Choice of Electronic Signal Transmission: The range of air pressure used for Signal Transmission in pneumatic system is limited by the dynamic operating range of the pneumatic devices used. But the choice of electrical transmission is much wider. Since either ac or dc current may be selected. In addition, a choice may be made between
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Temperature Controls using an Analog Electronic Controller: A Temperature Controls scheme using an Analog Electronic Controller of Fig. 21.14 is as shown in Fig. 21.16. The temperature setting, derived from a slide wire, is compared with the signal from a thermocouple situated in the oven being heated. The difference between these two voltages is amplified in an
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Analog Electronics Process Controllers: An Analog Electronics Process Controllers must be capable of providing one or more of the three main methods of control, namely, Proportional, Integral and Derivative. The circuits described in this section use high gain OPAMP’S with specially designed feedback circuits. They operate with their phase inverting input as a virtual earth
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Define Offset Error: Define Offset Error – Proportional control action is characterized by a permanent residual error in the operating point of the controlled variable when a change in load occurs. This error is called the OFFSET. The offset can be reduced by selecting higher value of controller gain (KP) corresponding to narrow bandwidth. Figure 21.6
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Proportional Controller: In many processes, the cycling that occurs with the two position ON—OFF control is undesirable. Steady process controlled in the absence of noises, is possible when the controlled variable is a continuous function of the error. A most widely used form of continuous control mode is the proportional control action, in which a
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On Off Controller or Two Position Controller: The On Off Controller or two position controller is the simplest, cheapest and the most used controllers. It is used in domestic heating systems, refrigeration, water tanks, etc. When the measured variable is below the set point, the controller is ON and the output signal has maximum value.
Step Function Response: The step function response consists of applying an instantaneous change in the control means and then recording graphically the result of the change on the measured variable. This graphical record obtained in response to the step excitation is called the Process Reaction curve. Two typical process reaction curves are shown in Fig.
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Basic Automatic Control: Multivariable systems are used more commonly in this age of Basic Automatic Control. Control parameters are becoming more complex by the day and the range of applications wider. In such complex systems, there are more than one input along with noise signals which are also present and there are more than one
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Standing Wave Ratio Measurements: Standing wave are created along the length of a transmission line due to the mismatch between the characteristic impedance Z0 and the terminating impedance of the transmission line. The actual voltage E on the line at any point is the sum (Ei + Er) of the voltage of the incident and
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