Category: Education
-
6.4 Other types of instruments
So far we have just looked at instruments that sense, control, and influence process variables. Transmitters, controllers, and control valves are respective examples of each instrument type. However, other instruments exist to perform useful functions for us. 6.4.1 Indicators One common “auxiliary” instrument is the indicator, the purpose of which is to provide a human-readable indication of…
-
6.3 Example: chemical reactor temperature control
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 Diagram) shows the inter-relationships of the process piping, vessels, and instruments: The purpose of this…
-
6.2 Example: wastewater disinfection
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 is not good to mix too little chlorine in the outgoing water (effluent) because we…
-
6.1 Example: boiler water level control system
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 “steam ejectors”), and augmenting chemical processes (e.g. reforming of natural gas into hydrogen and carbon…
-
Chapter 6. Introduction to industrial instrumentation
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 us. This chapter explains some of the fundamental principles of industrial instrumentation. The first step,…
-
5.7 Transfer function analysis for AC
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, we express both the output of a system and the corresponding input of that system…
-
5.6 The s variable to analyze AC circuit
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 included here. 5.6.1 Meaning of the s variable As we saw previously, Euler’s Relation allows us to express…
-
5.5 Phasors to represent AC Current
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 are based on the concept of complex numbers: combinations of “real” and “imaginary” quantities. The purpose…
-
5.4 Transformers
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 impedance matching) and even sensor circuits (sensing physical position). 5.4.1 Basic principles Before exploring the operation…
-
Chapter 5 AC electricity
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 use transformers to easily and efficiently step voltage up or down at will. If an electro-physical sensor…
-
4.13 Working of Inductors in dc circuits
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 the Henry (H). Inductors are devices expressly designed and manufactured to possess inductance. They are typically constructed of…
-
4.12 Working Of Capacitor In DC circuits
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 is measured in the unit of the Farad (F). The relationship between capacitance, stored electric charge (Q),…
-
4.11 Electromagnetism And DC Motor Principle
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 around that path. If the electric current travels in a circular path (i.e. through a…
-
4.10 Null-balance voltage measurement
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 another, used to measure light intensity. Glass pH electrodes are yet another, used to measure…
-
4.9 Bridge circuits
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 the diamond configuration is more common: The voltage source powering the bridge circuit is called…