Electronic measurements and instrumentation notes

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LECTURE NOTES ON EI1202 – MEASUREMENTS AND INSTRUMENTATION Ms.B.DEVI, L/ EEE N.P.R. COLLEGE OF ENGINEERING AND TECHNOLOGY, NATHAM. SYLLABUS UNIT I FUNDAMENTALS Functional elements of an instrument – Static and dynamic characteristics – Errors in measurement– Statistical evaluation of measurement data – Standards and calibration UNIT II ELECTRICAL AND ELECTRONICS INSTRUMENTS Principle and types of analog and digital instruments –Voltmeters – Ammeters - Multimeters – Single and three phase wattmeters and energy meters – Magnetic measurements – Determination of B-H curve and measurements of iron loss – Instrument transformers – Instruments for measurement of frequency and phase. UNIT III COMPARISON METHODS OF MEASUREMENTS D.C and A.C potentiometers – D.C and A.C bridges – Transformer ratio bridges – Self-balancing bridges – Interference and screening – Multiple earth and earth loops – Electrostatic and electromagnetic interference – Grounding techniques. UNIT IV STORAGE AND DISPLAY DEVICES Magnetic disk and tape – Recorders, digital plotters and printers – CRT display – Digital CRO, LED, LCD and dot-matrix display – Data Loggers UNIT V TRANSDUCERS AND DATA ACQUISITION SYSTEMS Classification of transducers – Selection of transducers – Resistive, capacitive and inductive transducers – Piezoelectric, optical and digital transducers – Elements of data acquisition system – A/D, D/A converters – Smart sensors. TEXT BOOKS 1. Doebelin, E.O., ―Measurement Systems – Application and Design‖, Tata McGraw Hill Publishing Company, 2003. 2. Sawhney, A.K., ―A Course in Electrical and Electronic Measurements and Instrumentation‖, Dhanpat Rai AND Co, 2004 REFERENCES 1. Bouwens, A.J., ―Digital Instrumentation‖, Tata McGraw Hill, 1997. 2. Moorthy, D.V.S., ―Transducers and Instrumentation‖, Prentice Hall of India, 2007. 3. Kalsi, H.S., ―Electronic Instrumentation‖, 2nd Edition, Tata McGraw Hill, 2004. 4. Martin Reissland, ―Electrical Measurements‖, New Age International (P) Ltd., 2001. 5. Gupta, J.B., ―A Course in Electronic and Electrical Measurements‖, S.K.Kataria and Sons, 2003. UNIT I FUNDAMENTALS Functional elements of an instrument – Static and dynamic characteristics – Errors in measurement– Statistical evaluation of measurement data – Standards and calibration QUESTIONS FUNCTIONAL ELEMENTS OF AN INSTRUMENT PART – A 1. What are the functional elements of an instrument? (2) 2. What is meant by accuracy of an instrument? (2) 3. Define international standard for ohm? (2) 4. What is primary sensing element? (2) 5. What is calibration? (2) 6. Define the terms precision & sensitivity. (2) 7. What are primary standards? Where are they used? (2) 8. When are static characteristics important? (2) 9. What is standard? What are the different types of standards?(2) 10. Define static error. Distinguish reproducibility and repeatability. (2) 11. Distinguish between direct and indirect methods of measurements. 12. With one example explain “Instrumental Errors”. (2) 13. Name some static and dynamic characteristics. (2) 14. State the difference between accuracy and precision of a measurement. (2) 15. What are primary and secondary measurements? (2) 16. What are the functions of instruments and measurement systems? (2) 17. What is an error? How it is classified? (2) 18. Classify the standards of measurement? (2) 19. Define standard deviation and average deviation. (2) 20. What are the sources of error? (2) 21. Define resolution. (2) 22. What is threshold? (2) 23. Define zero drift. (2) 24. Write short notes on systematic errors. (2) 25. What are random errors? (2) PART – B 1. Describe the functional elements of an instrument with its block diagram. And illustrate them with pressure gauge, pressure thermometer and D’Arsonval galvanometer. (16) 2. (i) What are the three categories of systematic errors in the Instrument and explain in detail. (8) (ii) Explain the Normal or Gaussian curve of errors in the study Of random effects. (8) 3. (i) What are the basic blocks of a generalized instrumentation system. Draw the various blocks and explain their functions. (10) (ii) Explain in detail calibration technique and draw the Calibration curve in general. (6) 4. (i) Discuss in detail various types of errors associated in Measurement and how these errors can be minimized? (10) (ii) Define the following terms in the context of normal Frequency distribution of data (6) a) Mean value b) Deviation c) Average deviation d) Variance e) Standard deviation. 5. (i) Define and explain the following static characteristics of an instrument. (8) a) Accuracy b) Resolution c) Sensitivity and d) Linearity (ii) Define and explain the types of static errors possible in an instrument. (8) 6. Discuss in detail the various static and dynamic characteristics of a measuring system. (16) 7. (i) For the given data, calculate a) Arithmetic mean b) Deviation of each value c) Algebraic sum of the deviations (6) X1 = 49.7, X2 = 50.1, X3 = 50.2, X4 = 49.6, X5 = 49.7 (ii) Explain in detail the types of static error. (7) (iii) Give a note on dynamic characteristics. (3) 8. (i) What is standard? Explain the different types of standards(8) (ii) What are the different standard inputs for studying the Dynamicresponse of a system. Define and sketch them. (8) UNIT II ELECTRICAL AND ELECTRONICS INSTRUMENTS Principle and types of analog and digital instruments –Voltmeters – Ammeters - Multimeters –Single and three phase wattmeters and energy meters – Magnetic measurements – Determinationof B-H curve and measurements of iron loss – Instrument transformers – Instruments formeasurement of frequency and phase. Principle and types of analog and digital instruments A multimeter ora multitester, also known as a volt/ohm meter or VOM, is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. Multimeters may use analogor digital circuits—analog multimeters and digital multimeters (often abbreviated DMM or DVOM.) Analog instruments are usually based on amicroammeter whose pointer moves over a scale calibration for all the different measurements that can be made; digital instruments usually display digits, but may display a bar of a length proportional to the quantity measured. A multimeter can be a hand-held device useful for basic fault finding and field service work or a bench instrument which can measure to a very high degree of accuracy. They can be used to troubleshoot electrical problems in a wide array of industrial and household devices such as electronic equipment, motor controls, domestic appliances, power supplies, and wiring systems. Multimeters are available in a wide ranges of features and prices. Cheap multimeters can cost less than US10, while the top of the line multimeters. History The first moving-pointer current-detecting device was the galvanometer. These were used to measure resistance and voltage by using a Wheatstone bridge, and comparing the unknown quantity to a reference voltage or resistance. While useful in the lab, the devices were very slow and impractical in the field. These galvanometers were bulky and delicate. The D'Arsonval/Weston meter movement used a fine metal spring to give proportional measurement rather than just detection, and built-in permanent field magnets made deflection independent of the 3D orientation of the meter. These features enabled dispensing with Wheatstone bridges, and made measurement quick and easy. By adding a series or shunt resistor, more than one range of voltage or current could be measured with one movement. Multimeters were invented in the early 1920s as radio receivers and other vacuum tube electronic devices became more common. The invention of the first multimeter is attributed to United States Post Office (USPS) engineer, Donald Macadie, who became dissatisfied with having to carry many separate instruments required for the maintenance of 1 the telecommunications circuits. Macadie invented an instrument which could measure amperes (aka amps), volts and ohms, so the multifunctional meter was then 2 named Avometer. The meter comprised a moving coil meter, voltage and precision resistors, and switches and sockets to select the range. Macadie took his idea to the Automatic Coil Winder and Electrical Equipment 2 Company (ACWEEC, founded in 1923). The first AVO was put on sale in 1923, and although it was initially a DC. Many of its features remained almost unaltered through to the last Model 8. Pocket watch style meters were in widespread use in the 1920s, at much lower cost than Avometers. The metal case was normally connected to the negative connection, an arrangement that caused numerous electric shocks. The technical specifications of these devices were often crude, for example the one illustrated has a resistance of just 33 ohms per volt, a non- linear scale and no zero adjustment. The usual analog multimeter when used for voltage measurements loads the circuit under test to some extent (a microammeter with full-scale current of 50ampere, the highest sensitivity commonly available, must draw at least 50 milliamps from the circuit under test to deflect fully). This may load a high-impedance circuit so much as to perturb the circuit, and also to give a low reading. Vacuum Tube Voltmeters or valve voltmeters (VTVM, VVM) were used for voltage measurements in electronic circuits where high impedance was necessary. The VTVM had a fixed input impedance of typically 1 megohm or more, usually through use of a cathode follower input circuit, and thus did not significantly load the circuit being tested. Before the introduction of digital electronic high-impedance analog transistor and field effect transistor (FETs) voltmeters were used. Modern digital meters and some modern analog meters use electronic input circuitry to achieve high-input impedance—their voltage ranges arefunctionally equivalent to VTVMs. Additional scales such as decibels, and functions such as capacitance, transistor gain, frequency, duty cycle, display hold, and buzzers which sound when the measured resistance is small have been included on many multimeters. While multimeters may be supplemented by more specialized equipment in a technician's toolkit, some modern multimeters include even more additional functions for specialized applications (e.g., temperature with a thermocoupleprobe, inductance, connectivity to a computer, speaking measured value, etc.). Quantities measured Contemporary multimeters can measure many quantities. The common ones are:  Voltage, alternating and direct, in volts.  Current, alternating and direct, in amperes. The frequency range for which AC measurements are accurate must be specified.  Resistance in ohms. Additionally, some multimeters measure:  Capacitance in farads.  Conductance in siemens.  Decibels.  Duty cycle as a percentage.  Frequency in hertz.  Inductance in henrys.  Temperature in degrees Celsius or Fahrenheit, with an appropriate temperature test probe, often a thermocouple Digital multimeters may also include circuits for:  Continuity; beeps when a circuit conducts.  Diodes (measuring forward drop of diode junctions, i.e., diodes and transistor junctions) and transistors (measuring current gain and other parameters).  Battery checking for simple 1.5 volt and 9 volt batteries. This is a current loaded voltage scale. Battery checking (ignoring internal resistance, which increases as the battery is depleted), is less accurate when using a DC voltage scale. Various sensors can be attached to multimeters to take measurements such as:  Light level  Acidity/Alkalinity(pH)