Tag: Industrial control
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Key Requirements for Industrial Control Computers
A computer is often used as part of a control system. The input data is typically from the operator’s commands and signals from the plant (flows, pressure, temperatures, limit switches, etc.). The output data comes in form of control actions to the plant and status displays to the operator. The instructions fed into the computer…
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A Basic Introduction to Ladder Diagrams for PLC Programming
The ladder diagram which is a special type of wiring diagram consists of two power rails, which are placed vertically on each side of the diagram, and rungs, which are placed horizontally between the power rails. The power rails are the source of power in the circuit (ac or dc), where the left rail is…
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What are Control and Instrumentation Cables?
While power cables are what we can refer to the “arteries” of industry, control and instrumentation cables are its “nerves” and are used for the control of equipment and data collection. They range from switch-core cables utilized in the wiring of control panels and switchgear, to the complex control and instrumentation cables employed in power…
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Key Causes of Uncertainty in Control Systems
One of the objectives of a control system is to achieve good plant performance in the face of uncertainty. The major sources of uncertainty in control are: Unmeasurable Perturbations Unmeasurable perturbations produce output deviations. With a controller in place, the achieved deviations must be below a user-defined bound. Modelling Errors Modelling errors can be classified…
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How Synchros are used as Position Transducers
Let’s consider the transformer in Figure 1.0 whose secondary winding can be rotated with the respect to the primary winding. At an angle ϴ, the output voltage will be given by: Vo = KVicosϴ where K is a constant The output amplitude is dependent on the angle, and the signal can be in phase or…
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Centralised vs. Decentralised Control Systems
Centralised control is usually carried out via computer software, having as inputs all the available sensors and producing signals for all the available actuators in the system. This control strategy is the most powerful, at least in theory, capable of extracting “optimal” performance. However, in practice, it requires non-standard apparatus (industrial computer data acquisition cards,…
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Actuators as Automation Components
An actuator is normally controlled by the controller. The actuator, in turn, changes the output of an automated process. The actuator in an automated process may in actual fact be several actuators, each of which provides an output that drives another in the series of actuators. Let’s consider the hydraulic actuator that controls the position…
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Adaptive Control System
Adaptive control system adjusts to changes and modifies its parameters to fit the prevailing circumstances. The adaptive control system is based on the use of a microprocessor as the controller. Such a device enables the control mode and the control parameters employed to be adapted to fit the prevailing circumstances, modifying them as the circumstances…
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Control Modes in Automation Systems
The mode of control is the way in which a control system makes corrections relative to an error that exists between the setpoint of a controlled variable and its actual value. We have a number of ways (i.e. control modes) by which a control unit can react to an error signal and supply an output…
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The Performance Limits for PID Controllers
PID Controllers can be applied successfully to most control problems in process control, electrical drive systems and servo mechanisms due to the fact that most of these processes have a dynamic behaviour that can be adequately approximated by a second-order process. However, the PID controller is not enough to control processes with additional complexities like…