• Sometimes we encounter a diversity of instrument signal standards in one control system. Such is the case with the following chemical reactor temperature control system, where three different signal standards convey information between the instruments. A P&ID (Process and Instrument…

  • The final step in treating wastewater before releasing it into the natural environment is to kill any harmful microorganisms (e.g. viruses, bacteria) in it. This is called disinfection, and chlorine gas is a very effective disinfecting agent. However, just as it…

  • Steam boilers are very common in industry, principally because steam power is so useful. Common uses for steam in industry include doing mechanical work (e.g. a steam engine moving some sort of machine), heating, producing vacuums (through the use of…

  • Instrumentation is the science of automated measurement and control. Applications of this science abound in modern research, industry, and everyday living. From automobile engine control systems to home thermostats to aircraft autopilots to the manufacture of pharmaceutical drugs, automation surrounds…

  • An extremely important topic in engineering is that of transfer functions. Simply defined, a transfer function is the ratio of output to input for any physical system, usually with both the output and input being mathematical functions of s. In other words,…

  • A powerful mathematical concept useful for analyzing practically any physical system – electrical circuits included – is something called the s variable. The s variable is closely related to Euler’s Relation and phasor expressions of waveforms, which is why a discussion of it is…

  • Phasors are to AC circuit quantities as polarity is to DC circuit quantities: a way to express the “directions” of voltage and current waveforms. As such, it is difficult to analyze AC circuits in depth without using this form of mathematical expression. Phasors…

  • The transformer is one of the most important components in all of AC circuitry. Principally used to “step” between different values of AC voltage and current in power systems, transformers find uses in many other types of circuits including electronic amplifiers (for…

  • While direct current (DC) refers to the flow of electrical charge carriers in a continuous direction, alternating current (or AC) refers to a periodic reversal of charge flow direction1 . As a mode of transferring electrical power, AC is tremendously useful because it allows us to…

  • Any conductor possesses a characteristic called inductance: the ability to store energy in the form of a magnetic field created by an electric current flowing through that conductor. Inductance is symbolized by the capital letter L and is measured in the unit of…

  • Any two electrical conductors separated by an insulating medium possess the characteristic called capacitance: the ability to store energy in the form of an electric field created by a voltage between those two conductors. Capacitance is symbolized by the capital letter C and…

  • The fundamental principle of electromagnetism is that an electric current will create a magnetic field at right angles to the direction of the current. If the electric current travels in a straight path, the lines of magnetic flux will form concentric circles…

  • A number of different sensors used in instrumentation generate DC voltage signals proportional to the process variable of interest. We call such sensors potentiometric, which literally means “voltage-measuring”. Thermocouples are one type of potentiometric sensor, used to measure temperature. Photodiodes are…

  • A bridge circuit is basically a pair of voltage dividers where the circuit output is taken as the difference in potential between the two dividers. Bridge circuits may be drawn in schematic form in an H-shape or in a diamond shape, although…

  • Perhaps the most valuable skill an instrument technician can possess is the ability to efficiently diagnose malfunctioning systems: determining in as short a time as possible the cause of a system’s malfunction. Since most instrumentation and control systems are based…

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