Introduction To Instrumentation And Measurements

Question: Explain what a measurement system is with the aid of a block diagram. You need to explain the main system elements and the process of the system. The primary sensor: Signal Conditioning: Data transmission : Display or Presentation: An example of how a measuring system works : Compare the following types of transmission systems and give examples of their usage: (a) Coaxial cable (b) Twisted-pair cable (c) Flat cable (d) Fibre-optic Answer: The measuring system: A system which is designed to specify anything which can be measured is called a measuring system. It involves the selection of unit of measurements comparing the quantity with the standard unit. The standard chosen should be of the same of nature as the quantity to be measured. Examples of measuring systems: Temperature: reservoir temperature, Building temperature. Measurement System: resistance thermocouple is used to measure the reservoir temperature and QAA made sensor is used to measure the building temperature. Pressure: High pressure, vacuum Measurement system: for vacuum measurement ionization gauge is used and high pressure is measured using gauges. Measuring System Elements Primary sensing elements: Primary sensing element is the first element which makes first contact in measurement system. Then, the signal is converted into electrical signal but it is limited to theoretical purpose only. Transducers are the elements which converts physical signals into electrical signals. Variable conversing element: The signal output from the primary sensing element may be of any kind. It may be electrical or any mechanical signal. Sometimes there is an error in output signal and we are not able to get output. For any instrument it is very important to convert the output signal in specified or desired results. Variable manipulation elements: It is just a change of numerical value to the electrical signals. Its main function is to makes the duplicate signal and preserving the original signals. Voltage amplifier is the perfect example of variable manipulation elements. Signal conditional element: Signals received from transducer have some information which is further verified in the system. There can be some signal distortions which are then purified with the help of amplifiers. In the amplification process, the amplitude of the signal is increased with the help of levers, gears, and electronic, pneumatic, and hydraulic amplifiers. This increase in the amplitude is named as gain. Data transmission elements: The signal element carried from the signal conditioning elements produces an output later with the help of transmission elements. If we take the examples of air traffic controls air planes are separated by the control system but they are connected by data transmission elements. Data presentation elements: It is the last stage of presenting the data transmission. At this step all the signal wave forms are presented on virtual display on TV screen or LED monitor. CRT and oscilloscope are also the examples of display. Here is the block diagram of measuring elements : Functional elements of pressure gauge: If we take the example of pressure gauge there is bourdon tube, which is very good example of measurement system. In this, air is entered through bourdon tube then air reaches through a link. Here, with the help of air link is jerked which affects the sector pinion. The Pressure will be indicated on the gauge with the help of these gears moves. Functional elements of thermometer: Thermometer is another example of measuring system. In thermometer, mercury act sas a primary sensing element. When mercury comes in contact with heat it expands and due to this reason mercury rises up we get the desired reading. Co axial cable: It consists of centre conductor surrounded by dielectric core. The braided shield surrounds the core and jacket protects the shield. This type of cable is generally used for communication purpose. It can be also used for the transmission purpose of data. Sometimes telephones companies also used these types of cables. It is called so just because of it carries the signal surrounded by another concentric channel. Twisted pair cables: The most common wire in the data communication is the twisted pair cable. It is a medium transmission cable consisting of two insulated wire arranged in regular spiral pattern. These cables can also be used for telephonic communication. It can supports to 10 TO 1000 Mbps. It can be used in Ethernet networks. It helps to lower the cable susceptibility most modern Ethernet networks. Flat cables: Flat cables are also known as ribbon cable. It is most widely used in computer data transmission. It consists of plastic base film with metallic wire inside. NASA also used these cables in space mission so that it would be easy for the data transmission made contact with astronauts. Fibre cable: Flat cables are long thin strands of very pure glass. They are arranged in bundles called optical cables used to transmit the light signals. There are 3 parts: Core: the centre of fibre where the light travels. Cladding: outer optical material surrounding the core. Buffer coating: plastic coating that protects the fibre from damage. Optical fibre cable Comparission Of Transmission Systems FACTORS COAXIAL CABLES TWISTED CABLES FLAT CABLES FIBRE CABLES Capacity It can transfer data 10 to 1000 Mbps It is having wide bandwidth In this quantity of band width is low It is having ling bandwidth. Uses It can be used for internet connection For telephonic purpose Can be used for TV transmission It can be used for high band width Shapes size Copper wire with metal jacket In single circuit two conductors Two conductor cable Fibre made of glass Advantage High data transfer Very thin cable Smaller than co-axial cable Only for long distance communications Disadvantage Signal leakage problem is there Electromagnetic interference It must be kept away from metal objects Complex structure of wire References: Introduction to instrumentation and measurements, Northrop Robert B Second edition. CRC Taylor Francis, USA; 2005. ISBN 0-8493-3773-9 Principles of Measurement and Instrumentation, A. S. Morris, Prentice Hall, 1993, Second Edition, ISBN 0-13-489709-9. Craig, E. (1993). Electronics via waveform analysis. New York: Springer-Verlag. Christopoulos, C., Wright, A. and Wright, A. (1999). Electrical power system protection. Dordrecht, Netherlands: Kluwer Academic. Bird, J. (2003). 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