Tag: process control
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Instrumentation and Controls for a Steam Desuperheater
A steam generator is an item of plant equipment that is found in almost every manufacturing site, and its output of steam has many critical uses in a variety of production processes. Steam has been assigned a measurement quality and a scale based on what is known as its dryness, which indicates how much “free”…
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The Instrumentation for Furnace Control
The figure below shows a typical basic furnace used to raise the temperature of a heat-transfer medium that is used on other equipment in a plant process. From the figure above, the temperature of the heat-transfer medium is the parameter that sets the demand on the heating system. The amount of heat required is manually…
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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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Electric Solenoid Actuator – Features & Operation
A typical electric solenoid actuator consists of a coil, armature, spring, and stem. This is illustrated in the figure below: The coil is connected to an external current supply. The spring rests on the armature to force it downward. The armature moves vertically inside the coil and transmits its motion through the stem to the…
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Pressure Control Valve Operation
A pressure control valve is a spring-loaded valve that is capable of maintaining a constant pressure in a system regardless of the flow rate. This is important, since most pumps e.g. gear pumps are constant-displacement types – a constant volume of fluid is pumped for each revolution of the pump shaft. If the pump were…
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Key Factors to Consider in Selection of Valves
Valves are the final element in a control loop, and are critical in providing the correct flow. The valve, usually operates in very harsh conditions, and is one of the most costly elements in the process control system. Their selection and correct installation require both knowledge and experience. Understanding system requirements and manufacturers specifications is…
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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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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 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 of inputs (both analog and digital) and control a small number of outputs or the…