Author: John Mulindi
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Combustion & Temperature Control for a Direct-Fired Process Heater
The figure below shows the control schemes applied to a direct-fired process heater. From the diagram above, the heat from the burning fuel is applied directly to the tubes carrying the process fluid in similar way as the water tubes in a steam generator. This type of heater is usually used as a reboiler in…
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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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Key Facts about RS-485 Industrial Network
RS-485 network is used in many industrial applications to gather data and control addressable motor drives, PLCs, cameras, time clocks, barcode scanners for process control and other factory automatic apparatus. RS-485 devices can be connected to a computer and multi-dropped at various locations in a network style configuration. The devices can be up to 4000…
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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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How to Minimize Water Vapor in Instrument Air/Pneumatic Systems
Water is one of the most common contaminants in instrument air systems, causing corrosion of metal components and as a result clogging of orifices. Special devices referred to as air dryers installed in instrument air systems use solid materials called desiccants to absorb water entrained in the compressed air. The desiccant material is “regenerated” by…
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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…