Tag: instrumentation and control
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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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The General Principle of using a Servo Motor for Position Control
Servo motors are typically employed in closed-loop position control; for example let us consider the following application, where the angular position of the output shaft is intended to follow the reference voltage (ϴref). The potentiometer mounted on the output shaft provides a feedback voltage proportional to the actual position of the output shaft. The voltage…
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Designing a System to Measure & Display a Shaft Rotation Speed
We would like to design a system to measure and display the rotational speed of a shaft. To accomplish this, we shall use a number of integrated circuits (ICs) to create the desired functionality of this system. A simple technique to measure the speed is to count the number of shaft rotations during a given…
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Analog vs. Digital Controllers
Analog signals pass continuously through a full range of values for example a measuring device converts the process variable (PV), say temperature, into a signal corresponding to this temperature. Each temperature value corresponds to a value of the electrical signal. Digital signals belong to the group of discrete signals; here the individual signals are represented…
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What is a Microsyn Transducer?
This is a variable-reluctance transducer used to detect small motions, giving output signals as low as 0.01° of changes in angles. The figure below shows an example of Microsyn: In the Microsyn transducer above, the coils are connected in such a way that at the null position of the rotary element, the voltages in coils…
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Steam-heated Reboiler Control System
When steam-heated reboilers are used in distillation columns and the heating medium is steam, a flow control loop for the steam will typically be incorporated. The control valve can then be placed either in the steam or condensate line. Steam pressure compensation is always recommended in these cases, and the controls are illustrated in the…
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Furnace Control System for a Rapidly Changing Demand
Let’s consider the figure below: In the system above, the output of temperature controller TC represents the process demand, and this signal is applied as one of the inputs, each to a high (>) and a low (<) signal selector block (module). The second input to the high (>) selector is obtained from the measurement…
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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”…