Tag: control systems
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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 … Read more
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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. Figure (a) computer control of a turbo generator unit Typical output variables … Read more
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How Controllers are used in Industrial Automation Systems
In many process control systems, microprocessor based programmable logic controllers are used for decision making due to the sophistication of the system and the large number of process variables involved. The PLC can be configured to receive a small number … Read more
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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 … Read more
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Basic Features of Modern PID Controllers
Most modern PID controllers have the following features: Manual versus automatic modeOutput trackingSetpoint trackingAlarm capabilitiesProcess variable (PV) characterization and dampingSetpoint limitsOutput limitsPID tuning security Manual and Automatic Modes When the controller manually calculates … Read more
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Direct Digital Control (DDC)
In direct digital control (DDC) a single computer is able to carry out PID control for multiple loops at the same time make that loop data accessible between loops for purposes of cascade control, feedforward control, ratio control… Read more
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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 … Read more
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Feedforward Control
Feedforward control is based on principle of pre-emptive load counter-action i.e. if all major loads (i.e. disturbances) on a process variable are monitored, and their effects on that process variable are well-understood, a control system programmed to take the appropriate … Read more
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Benefits of Cascade Control
We know very well that closed loop control provides increased performance over open loop control. So it would be rational to expect benefits from adding inner control loop around plant items that have degrading overall performance. The Figure (a) below … Read more
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The Basics of Ladder Diagrams for Programming PLCs
The ladder diagrams are universally used as a symbolic and schematic way to represent the interconnection between the elements in a Programmable Logic Controller (PLC). The ladder network is also used as a tool for programming the operation of PLC. … Read more