1.1 Introduction to measurement and instrumentation 1.1.1 Measurement Measurement refers to the process of comparing unknown quantity with the standard one. It provides us with the means for describing chemical and physical parameters of materials quantitatively. Therefore, when one mentions the word measurement, what comes into the mind is the weight, length, distance, time, height, temperature, color of a material. The standard used for measurement should be accurate and internationally accepted. It also important that the experimental procedure adopted while performing the measurement should be scientifically provable. The International System of Units (SI) defined seven base units of measurement known as the SI base units. The SI base units are; Table 1. 1 The seven Base Units Quantity SI unit Symbol Length Metre m Time Second s Mass Kilogram kg Electric Current Ampere A Thermodynamic Temperature Kelvin K Luminous Intensity Candela cd Amount of Substance Mole mole The base units are the building blocks of the system. All the other units are derived from the base units and are known as SI derived units and the quantity as the SI derived quantity. There are unlimited number of SI derived quantities and units. An example of the SI derived quantity is the velocity (with the derived unit as m/s) which is derived from dividing length by time. 1.1.2 Instrumentation Instrumentation refers to the technology of using instruments to measure and control physical and chemical properties of a system. It is important for monitoring and maintaining the operation of a system within the design expectations so as to achieve good quality, safety and efficiency of the process. It helps achieve automatic control of process there by reducing the dependency on human labor. Measurement and instrumentation are very essential to system control. Be it a spaceship, air conditioner, aircraft, etc. they all rely on measurement and instrumentation in order to make a decision. We are going to construct a number of instruments for measurement and use them to achieve automatic control of systems. 1.2 Functional Elements of a Measurement System (Instrument) The functional elements of a measurement system are; 1.2.1 Sensing element This is the primary sensing object on the instrument. An element that is sensitive to the variable being measured. It is the first part of the instrument to sense or detect the measurement and then produces an output that is proportional to the measurement. 1.2.2 Transducer (Variable Conversion) element The output signal of the sensing element can be of any form. Sometimes, this output is not suited to the measurement system. The transducer element converts the signal from one physical form to another while maintaining the information content of the original signal. 1.2.3 Variable manipulation element Variable manipulation element modifies the signal presented to it while preserving the original nature of the signal. It does this by amplification, attenuation and filtration so that the desired output is produced. 1.2.4 Signal conditioning element Signal conditioning involves the removal of the unwanted noise and distortion from the signal through filtration. 1.2.5 Data transmission element In a situation whereby the elements of an instrument are physically separated, it becomes necessary to transmit data from an element to another. The data transmission element transmits data from one location to another while preserving the information content of the data. 1.2.6 Data presentation element This is the element that provides record or indication of the output on a measurement instrument. If the data is to be monitored, visual display devices are necessary. In case the data is to be recorded, recorders like SD cards, magnetic tapes, and high speed camera are necessary. 1.3 Input-Output configuration of a measurement system A measurement instrument performs an operation on measured input (i) to provide an output (o) called measurement. The performance of the instrument can be expressed in terms of the operational transfer function (G). The relationship between the input and output is characterized by the transfer function such that; There are three categories of inputs in a measurement system; 1.3.1 Desired input This is the quantity that the instrument is intended to measure during the measurement. 1.3.2 Interfering input This is the quantity that the instrument is not intended to measure but the instrument is unintentionally sensitive to the quantity. 1.3.3 Modifying input This quantity takes into account the desired and interfering inputs to modify the input-output relation. Generalization of the Measurement System The measurement system can be generalized into input stage, intermediate stage and output stage according to the figure below; Fig. 1. 1 Generalization of the measurement system 1.4 Performance characteristics of a measurement system The following terms are used to describe the performance characteristics of an instrument; 1.4.1 Accuracy Taking into account that no instrument gives the exact value of what is being measured, there is always uncertainties in the measured values. Accuracy refers to how close the measured value is to the true value. 1.4.2 Calibration These are the procedures undertaken to for checking and adjusting instrument’s scale so that the readings conform to an accepted standard. 1.4.3 Repeatability This describes how close the outputs are when the same input under the same conditions are applied repeatedly. 1.4.4 Range and Span Range is the region between the limits within which a measuring instrument is designed to operate, while the span represents the algebraic difference between those upper and lower limits. 1.4.5 Precision This is the ability of the measuring instrument to give a certain group of readings with a certain accuracy. 1.4.6 Sensitivity This is expressed as a ratio of the output signal to the input signal. 1.4.7 Speed of response This is the rapidity within which an instrument responds to the quantity being measured. 1.5 Introduction to Control Systems Before we consider a control system lets first consider the following two terms; 1.5.1 System A system is an assemblage of devices connected to form an organized structure in order to perform a specific task. 1.5.2 Control The ability to influence, direct, command or regulate the behavior of a system or course of events. 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