Category: Control Systems
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Analog vs. Digital Controllers
Analog signals pass continuously through a full range of values for example a measuring device converts the process variable (PV), say temperature, into a signal corresponding to this temperature. Each temperature value corresponds to a value of the electrical signal. Digital signals belong to the group of discrete signals; here the individual signals are represented…
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Position Control System using a Microprocessor-Based Controller
Consider the following figure illustrating a position control system employing a microprocessor-based controller with parallel ports: The system above has one output port and three input ports (each port has its own address). The output port is partitioned: Six bits are converted in a Digital Analog Converter (DAC) to provide the analog motor-drive signal, the…
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Analog Proportional Controller
An analog controller typically employs op-amps to provide the necessary gain and signal processing. Let’s consider the flow control system below: In the system above, the controller’s function is to maintain the flow of a liquid through a pipe at 6 gallons/minute. This system consists of: The flow valve is operated with a signal…
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Basic Steps to Consider in Designing a Control System
Typically a control system should be designed to work together with an already existing process. The control design problem can be stated at local, supervisory or even plant-wide level. If we consider the local level, the typical steps in designing the control are: Most of these activities should be performed iteratively. For example, if the…
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Fuzzy Controller and its Industrial Applications
Fuzzy logic is a human model, potentially applicable to a wide range of processes and tasks that require human instinct and experience. In computer, truth-values are either 1 or 0, which corresponds to true/false duality. In fuzzy logic, truth is the matter of degree, hence truth-values ranges between 1 and 0 in a continuous manner.…
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Transfer Functions and Block Diagrams of Control Systems
Transfer Functions A transfer function is a mathematical formulation that relates the output variable of a device to the input variable. For linear devices, the transfer function is independent of the input quantity and solely dependent on the parameters of the device together with any operations of time, such as differentiation and integration that it…
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A Digitally Controlled Drill Press
The diagram below shows a digital control system for a drill press that includes: the input, digital processor, drill-positioning mechanisms, and sampled-data position control system. The process is controlled as follows: The processor receives the input data and determines the sequence of operations while storing both the sequence and the hole positions in the memory.…
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Basic Elements of a Digital Controller for a Steam-Turbine Driven Generator
The block diagram below illustrates the basic elements of a minicomputer system for speed and voltage control as well as data acquisition of a steam-turbine driven generator unit. Typical output variables of the generator are speed, rotor angle, terminal voltage, field (excitation) current, armature current, and real & reactive power. A number of output variables…
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How to Tune the PID Controller
Before we discuss how to tune the PID controller, let’s look at some basic facts about PID Controller. Basic Facts about PID Controller Many control systems use a combinational of three types of control i.e. Proportional + Integral + Derivative (PID) control. The foundation of the system is the Proportional Control, adding Integral Control provides…
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Ratio Control
In some processes, it is a common requirement for two flows to be kept in precise ratio to each other for example, a gas or oil and air in combustion control, and reagents being fed to a chemical reactor hence the need for ratio control. In simple ratio control, one flow is declared to be…