Tag: instrumentation and control
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Industrial Process Temperature Control System
Let’s consider the industrial process control system shown below: The requirement is to control the temperature ϴ in the tank. The voltage r, obtained from a potentiometer, is calibrated in terms of the desired temperature ϴc. This voltage represents the input quantity to the feedback control system. The actual temperature ϴ, the output quantity, is…
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How to Perform Mass flow Measurements with DP sensors
Let’s assume we are measuring flow by differential-creating primary device for example an orifice plate and a DP cell as illustrated in Figure 1 below: The differential head across the primary device is corrected for temperature variation in the first calculation block, but there is no need for pressure correction because a liquid is virtually…
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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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Null vs. Deflection Type Instruments
Null Instrument The null technique is one of the operational modes for a measuring instrument. A null instrument employs the null method for measurement. In this technique, the instrument exerts an influence on the measured system so as to oppose the effect of the measurand. The influence and the measurand are balanced until they are…
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Analog vs. Digital Sensors
Analog Sensors Analog sensors provide a signal that is continuous in both its magnitude and its temporal (time) or spatial (space) content. Most physical variables such as, current, pressure, temperature, displacement, acceleration, speed, light intensity and strain tend to be continuous in nature and are readily measured by an analog sensor and represented by an…
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What are PLC-Based Water Treatment Plants?
Most of the water treatment plants in the previous decade were manually operated. However, they were automated to a certain degree using relays or electrical control panels but the system was not reliable and required a lot of space. In this modern era, water treatment facilities are automatically operated using PLC or Programmable Logic Controllers…
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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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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…