Author: John Mulindi
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What is Selective Control?
In a number of process control problems, we may have more measurements (controlled variables) than manipulated variables. Hence, it is impossible to eliminate errors in all the controlled variables for arbitrary setpoint changes of disturbances by using only simple (single-input/single output) controllers. Thus selectors are used to share the manipulated variables among the controlled variables.…
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5 Control Techniques – Their Features & Applications
We have a number of control theories that have been put forward on how to design control laws to accomplish various purposes. Generally they can be classified as follows: Classical Control This control technique deals with the behaviour of dynamical systems, which typically have inputs and how their behaviour is modified by feedback, employing the…
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4 Types of Radiation & How they interact with Matter
We have four key types of radiation, namely: alpha, beta, gamma and neutron. The four types differ in mass, energy and how deep they penetrate objects. Alpha Particle The alpha particle (α) is a helium nucleus produced from the radioactive decay of heavy metals and some nuclear reactions. Alpha decay often occurs among nuclei that…
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How Photoelectric Effect Impacts p-n Junctions
When light strikes a semiconductor p-n junction, its energy is absorbed by electrons. Electrons and holes generated by light in the p-n junction are swept by the junction electrical field. Consequently, the current flows through the junction. The figure below illustrates the process of generating current in a photodiode. The figure above is a p-n…
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Gamma Spectroscopy Measurement Technique
Gamma spectroscopy is a radiochemistry measurement technique that determines the energy and count rate of gamma rays emitted by radioactive substances. A detailed analysis of gamma ray energy spectrum is used to determine the identity and quantity of gamma emitters present in a material. The apparatus used in gamma spectroscopy includes a detector, a pulse…
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Hierarchical Control Strategies for a Process Plant
In a process plant, we typically have a number of control goals that require different algorithms and types of information from the process; from the level closest to the process to the plant-wide control. All these activities ought to be connected; hence some kind of hierarchy is necessary. Local Control Local control uses information directly…
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Permanent Magnet DC Motors – Operation & Applications
Permanent magnet dc motors employ a permanent magnet instead of stationary field winding (as with the case of some other types of dc motors) for producing the required magnetic flux. These stationary magnets are normally fixed to the outer shell of the motor as illustrated in Figure 1.0. Features of a Permanent Magnet DC Motor…
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Passive vs. Active Sensors
Sensors are normally used to convert physical variables like pressure to signal variables. Sensors are also often termed to as transducers since they are devices that convert input energy of one form into output energy of another form. Sensors can be classified into two broad classes depending on how they interact with the environment they…
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Principle of Operation and Applications of a Laser Diode
Laser diodes are PN junction devices under a forward bias. LASER is an acronym for Light Amplification by Stimulated Emission of Radiation. Laser Diode Structure The laser diode structure can be divided into two categories: An example of an edge-emitting laser diode structure is shown in Figure 1.0 below. This type of structure is termed…