Measurements & Instrumentations

1. Measurements & Instrumentations Module 1

2. Grading policy • Participation 10 marks • Preparation, Promptness, Level of Engagement, Behavior • HWs 10 marks • Quizzes 10 marks • Practical 30 marks • Lab activities and Practical exam • IAT competency exams (practical and knowledge ) 40 marks

3. Preparation marks • Print the modules and cover it and bring it to every class with you • Calculator • Stationary • Lab coat

4. Participation Marks • Promptness: On time or Late • Level of Engagement • Behavior

5. Objectives • What is measurements • Measurements elements • Measurement methods / types

6. Introduction to measurements • All physical parameters are measurable, and the first step in any engineering process is measurement. • Measurement of abstract quantities like intelligence. • If we cannot measure something, we can not control it. This ‘something’ is referred to as a ‘physical quantity’.

7. Measurements forms • Physical dimensions of an object • Count of an object • Temperature of an object • Fluid pressure / flow rate / volume • Electrical voltage / current / resistors • Machine position / speed

8. What we are trying to measure ?

9. What is measurements ? • Measurement is the process of determining the magnitude of a physical quantity such as length or mass, relative to a standard unit of measurement, such as the meter. • It could be also defined as a comparison between a standard and a physical quantity to produce a numeric value Measurements Elements

10. Measuring Devices • The measuring devices could be sensors, transducers or instruments. • A ruler (length) • A thermometer (temperature) • A light dependent resistor (LDR) measures (light intensity)

11. Skill 1: Identify the measurement elements

12. Methods of measurement • The two basic methods of measurement are • Direct measurement • Indirect measurement.

13. Direct Measurement • In direct measurement, the physical quantity is compared directly with a standard.

14. Indirect Measurement • In an indirect type of measurement, the physical quantity measured is converted to an analog form that can be processed and presented. • For example, the mercury in the mercury thermometer expands and contracts based on the input temperature, which can be read on a calibrated glass tube. A bimetallic thermometer

15. Question

16. Recap • Define measurements • Measurements elements • Measurement types / methods

17. Warm up • Give an example of an error that occur when you are taking a measurement.

18. Objectives • Definition of the error • Types of the errors • Error analysis – mean & standard deviation • Calibration

19. Definition of the error • Error = Instrument reading – true value • Error types • Systematic errors • Random errors

20. Systematic Errors • The zero error of the instrument • The shortcomings of the sensor • Improper reading of the instrument due to the improper position of the person’s head/eye (Parallax error) • The environmental effect Parallax error demonstration

21. Systematic Errors • Systematic errors can be corrected by calibration. • Systematic errors can be traced and reduced

22. Random errors • Measuring the same quantity using the same instrument and every time you get different reading • Example of random error is • measuring the mass of gold on an electronic scale several times, and obtaining readings that vary in a random fashion.

23. Random errors • The reasons for random errors are not known and therefore can not be avoided • They can be estimated and reduced by statistical operations

24. Skill 2: Identify the type of measurement

25. Error analysis • Error analysis are done for the random error • Average / Mean • Standard Deviation

26. Error analysis • Measuring the same input variable a number of times, keeping all other factors affecting the measurement the same, the measured value would differ in a random way. • The readings normally follow a particular distribution and the random error may be reduced by taking the average or mean. • The average/mean gives an estimate of the ‘true’ value

27. Error analysis

28. Example 1 • A mass of gold is measured 5 times find the mean • Mean / Average =

29. Standard Deviation • The standard deviation, denoted by the letter ‘σ’ tells us about how much the individual readings deviate or differ from the average/mean of the set of readings.

30. Example 2

31. Example 3 • A diameter of a wire is measured by a group of students with a micrometer, and the reading are shown below: • Assuming that only random errors are present, calculate the following: • mean / Average • Standard deviation

32. Excersice

33. Recap • Error • Systematic Error • Random Error • Mean • Standard deviation

34. Warm Up • Define measurements • Measurements type • Error • Systematic Error • Random Error • Mean • Standard deviation

35. Instrument Performance Evaluation • Any measuring instrument/device has a set of specifications that inform the user of its function. • These characteristics are described in the catalogue or datasheet provided by the manufacturer

36. Accuracy • Accuracy of an instrument is how close a measured value is to the true value.

37. Precision • The ability of an instrument to give the similar reading when the same physical quantity is measured more than once • The closer together a group of measurements are, the more precise the instrument. • A smaller standard deviation result indicates a more precise measurement.

38. Small STD Large STD

42. Precision of the instrument Which one is more precise ?

43. Precision of the instrument Which instrument is more precise ?

45. Bias • The difference between the true value (TV) and average value (AV). • Ideally, the bias should be zero. • 𝑩𝒊𝒂𝒔 = 𝑻𝑽 − 𝑨𝑽

46. Example • A mass of silver is measured four times and the values are shown below. If it the true value is 6 kg, find the bias

47. Range • The range of an instrument defines the minimum and maximum values that the instrument can measure. Min value = -40oF Max value = 120 oF Range = 120oF – (-40oF) = 160oF

49. Sensitivity • The sensitivity of a measuring instrument is its ability to detect small changes in the measured quantity. • Sensitivity = Change in output (y-axis)/Change in input (x-axis)

50. Linearity • Some measuring instruments/devices output a signal that is proportional to the input physical quantity. • These instruments are called linear devices. • Other instruments that don’t have a proportional relationship between the output signal and the input are non-linear devices.