o Lecture (2 hours) / week Saturday, g1: (period 1) g2: (period 2) o Lab., Sec (2 hours)/week Saturday, g1: (period 4) Wednesday, g2: (period 3)

Transcription

1 1

2 o Lecture (2 hours) / week Saturday, g1: (period 1) g2: (period 2) o Lab., Sec (2 hours)/week Saturday, g1: (period 4) Wednesday, g2: (period 3) 2

3 This course introduces the principles of instrumentation and measurements. It explores the working principles of DC & AC meters, oscilloscope and signal generators as well as the operation and application of various sensors and transducers 3

4 o Introduce the fundamentals of measurements and instrumentation o Explain the working principle of DC & AC meters and measurements o Discuss the operation of oscilloscope and signal generator o Describe the working principle of various sensors and transducers o Explain the methodology of signal conditioning and data acquisition 4

5 o Able to Explain the fundamentals of measurements and instrumentation Explain the working principle of DC & AC meters Discuss the operation of oscilloscope and signal generator Describe the working principle of various sensors and transducers 5

6 Part 1 Measurements DC Measurement AC Measurement Oscilloscope Signal generator Part 2 Instrumentation Signal conditioning Signal transmission Sensors 6

7 o Northrop R.B., Introduction to Instrumentation & Measurement, 2 nd Ed., CRC Press, 2005 o Morris A.S., Measurement & Instrumentation Principle, Butterworth-Heinemann, 2001 o Kalsi H.S., Electronic Instrumentation, 2nd Ed., Tata McGraw-Hill,

8 Distribution Final Exam (40) Med-term (20) Term activity: (40) Quiz (4) (10) Laboratory (20) Attendance, Res. (Lec. Tut.) (10) 8

9 Introduction to Instrumentation and Measurements 9

10 Process of comparing an unknown quantity with an accepted standard quantity Estimation of the magnitude of some attribute of an object relative to a unit of measurement 10

11 Measurement standards Measurement errors Accuracy vs. precision Measurement Uncertainty 11

12 Based on definition of the seven fundamental SI units of measurement Categorized into four: International standard (SI) Primary standards Secondary (transfer) standards Working standards 12

13 Quantity Symbol Unit Symbol Length l meter m Mass m kilogram kg Time t second s Temperature T kelvin o K Electric current I ampere A Amount of Substance mole mol Luminous intensity candela cd 13

14 Quantity Symbol Unit Unit Abbre. Voltage (emf) V volt V Charge Q coulomb C Resistance R Ohm Ω Capacitance C farad F Inductance L henry H Above electrical units are derived from standard unit of measure for electric current 14

15 Deviation of a reading from the expected value of the measured variable Extent of measurement error must be stated with the measurement Error in measurement is expressed as absolute error or percentage of error 15

16 (e) Absolute error The difference between the expected (Yn) and the measured (Xn) value of a variable e = Y n - X n Percentage of error Yn - X Percent error = n (100) Y n 16

17 Divided into four categories: Gross Errors Systematic Errors Random Errors Limiting Errors 17

18 Generally the fault of the person using the measuring instrument such as incorrect reading, incorrect recording, incorrect use etc Avoidable and must be identified and minimized if not eliminated 18

19 Probable causes: Instrument error Environmental effect Observational errors Causes shall be identified and corrected 19

20 o Generally an accumulation of large numbers of small inherent causes o Shall be statistically analyzed and reduced o Prompt for better accuracy and precise instrument 20

21 Limiting Errors o Manufacturing limitation to the accuracy of an instrument o Stated as percentage of full-scale deflection o Increases as measured value less than full-scale deflection 21

22 Example: A 300-V voltmeter is specified to be accurate within ±2% at full scale. Calculate the limiting error when the instrument is used to measure a 120-V source. The magnitude of the limiting error is 2/100 x 300 = 6V Therefore, the limiting error at 120 V is 6/120 x 100 = 5% (reading < full scale, limiting error increased) 22

23 Accuracy vs. Precision Accuracy The degree of exactness of a measurement compared to the expected value Y n - X n A = 1 - Y n Precision A measure of consistency, or repeatability of measurements Precision = 1 - X n - X n X n Xn = the value of the nth measurement X n = the average of the set of n measurements 23

24 The expected value of the voltage across a resistor is 5.0V. However, measurement yields a value of 4.9V. Calculate: a) absolute error (0.1) b)% error (2%) c) relative accuracy (0.98) d) % accuracy (98%) 24

25 Probability that a reading falls within the interval that contain true value Confidence level for margin of errors Statistically determined Reflect instrument imprecision 25

26 omean value/ Arithmetic Mean odeviation oaverage deviation (D) ostandard deviation (S) 26

27 x x1 x 2 x 3 x n n n i1 x i n n x n x i = total number of piece of data = the value of the nth measurement = set of number 27

28 The difference between each piece of data and arithmetic mean d n x n x * Note d tot d 1 d2 dn 0 28

29 precision of a measuring instrument - high D low precision - low D high precision D d 1 d 2 n d n 29

30 The degree to which the value vary about the average value for n n d n x x S n i i n i i 30 for n 1 2 n d S n i i

31 For the following data compute (a) The arithmetic mean (49.9) (b) The deviation of each value (0.2,-0.2,-0.3,0.3) (c) The algebraic sum of the deviation (0) (d) The average deviation (0.25) (e) The standard deviation (0.294) x 1 = 50.1 x 2 = 49.7 x 3 = 49.6 x 4 =

32 Process of establishing the relation between the indication of a measuring instrument and the value of a measurement standard Traceability to International Standard Calibration improve accuracy 32

33 33