Tag: Industrial control
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Fuses & Circuit Breakers vs. Overload Heaters for Industrial Motor Protection
A key component of any motor control circuit is some kind of device to detect a condition of excessive overload and interrupt the power to the motor before thermal damage occurs to it. An overload heater is a simple and common overload protective device that consists of resistive elements connected in series with the three…
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How PLC Systems are Protected from Plant Voltages
Internally a PLC typically operates at 5 V dc. The external devices such as solenoids, limit switches, motor starters, etc. operate at voltages up to 110 V ac. The mixing of these voltages will cause irreparable damage to the PLC electronics. A less noticeable problem may occur from electrical noise introduced into the PLC from…
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Industrial Motor Control Using Contactors
Motor contactors are large, high-current rated electromechanical relays. These are special relays in the sense that, they have heavy duty contacts that can handle the motor’s inrush current over many start and stop cycles. The contactor is actuated by an electromagnetic solenoid (coil) which pulls the contacts closed when energized. They also have an arc-suppressing…
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Advantages of Fluid Power over Electric Power Systems
Generally fluid power systems tend to be insufficient, requiring much more energy input to the fluid than what is extracted at the points of use. When large amounts of energy need to be transmitted over long distances, electricity is a more practical medium for the task. Nonetheless, fluid power systems have certain advantages over electric…
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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,…