1. MMM Lecture 2

2. Inspection
Inspection is defined as a procedure in which a part or product characteristic, such as a dimension, is examined to determine whether it conforms to the design specification.
Basically inspection is carried out to isolate and evaluate a specific design or quality attribute of a component or product.
In inspection, the part either passes or fails. Thus, industrial inspection has become a very important aspect of quality control.

3. Inspection Inspection essentially encompasses the following:
Ascertain that the part, material, or component conforms to the established or desired standard.
Accomplish interchangeability of manufacture.
Sustain customer goodwill by ensuring that no defective product reaches the customers.
Provide the means of finding out inadequacies in manufacture. The results of inspection are recorded and reported to the manufacturing department for further action to ensure production of acceptable parts and reduction in scrap.

4. Inspection
Purchase good-quality raw materials, tools, and equipment that govern the quality of the finished products.
Coordinate the functions of quality control, production, purchasing, and other departments of the organizations.
Take the decision to perform rework on defective parts, that is, to assess the \ possibility of making some of these parts acceptable after minor repairs.
Promote the spirit of competition, which leads to the manufacture of quality products in bulk by eliminating bottlenecks and adopting better production techniques.

5. Measuring Instruments
Deflection and null type instruments
Analog and digital instruments
Active and passive instruments
Automatic and manually operated instruments
Contacting and non contacting instruments
Absolute and secondary instruments
Intelligent instruments.

6. DEFLECTION AND NULL TYPE
Physical effect generated by the measuring quantity
Equivalent opposing effect to nullify the physical effect caused by the quantity

7. ANALOG AND DIGITAL INSTRUMENTS
Physical variables of interest in the form of continuous or stepless variations
Physical variables are represented by digital quantities

8. ACTIVE AND PASSIVE INSTRUMENTS
Instruments are those that require some source of auxiliary power
The energy requirements of the instruments are met entirely from the input signal

9. Automatic and manually operated
Manually operated – requires the service of human operator
Automated – doesn't requires human operator

10. Contacting And Non Contacting Instruments
A contacting with measuring medium
Measure the desired input even though they are not in close contact with the measuring medium

11. Absolute and Secondary Instruments
These instruments give the value of the electrical quantity in terms of absolute quantities
Deflection of the instruments can read directly
A galvanometer is a type of ammeter: an instrument for detecting and measuring electric current. It is an analog electromechanical transducer that produces a rotary deflection of some type of pointer in response to electric current flowing through its coil in a magnetic field.

12. Intelligent instruments
Microprocessors are incorporated with measuring instruments

13. Characteristics of Measuring Instrument
Sensitivity
Readability
Range of accuracy
Precision

14. Definition
Sensitivity- Sensitivity is defined as the ratio of the magnitude of response (output signal) to the magnitude of the quantity being measured (input signal)
Readability- Readability is defined as the closeness with which the scale of the analog instrument can be read

15. Definition
Range of accuracy- Accuracy of a measuring system is defined as the closeness of the instrument output to the true value of the measured quantity
Precision- Precision is defined as the ability of the instrument to reproduce a certain set of readings within a given accuracy

16. Sensitivity
If the calibration curve is liner, as shown, the sensitivity of the instrument is the slope of the calibration curve.
If the calibration curve is not linear as shown, then the sensitivity varies with the input.

17. Sensitivity
This is the relationship between a change in the output reading for a given change of the input. (This relationship may be linear or non-linear.)
Sensitivity is often known as scale factor or instrument magnification and an instrument with a large sensitivity (scale factor) will indicate a large movement of the indicator for a small input change.

18. Sensitivity, K = 5 V/kN Output, Vo (V) Force, F Slope = 5 V/kN
Input, Fi (kN)
Slope = 5 V/kN
Load Cell
Force, F
Output, Vo
Block Diagram:
Input, F (kN)
Output, Vo (V) K
Sensitivity, K = 5 V/kN

19. Example
(1) A 0.01 W/A meter with 5 A fsd, Rm = W/A x A = 0.01 x 5 = 0.05 W Vmax across the Meter will be = 5 A x 0.05 W = 0.25 V for fsd. (2) A 0.1 W/A meter with 5 A fsd,will drop 2.5 V (i.e., it is 10 times less sensitive), which may bias the results

20. Readability
Readability is defined as the ease with which readings may be taken with an instrument.
Readability difficulties may often occur due to parallax errors when an observer is noting the position of a pointer on a calibrated scale

21. Readability
What is the value ?

22. Accuracy
Accuracy = the extent to which a measured value agrees with a true value
The difference between the measured value & the true value is known as ‘Error of measurement’
Accuracy is the quality of conformity

23. Example: Accuracy
Who is more accurate when measuring a book that has a true length of 17.0 cm?
A :
17.0 cm, 16.0 cm, 18.0 cm, 15.0 cm
B ::
15.5 cm, 15.0 cm, 15.2 cm, 15.3 cm

24. Precision
The precision of a measurement depends on the instrument used to measure it.
For example, how long is this block?

25. How big is the beetle? Measure between the head and the tail!
Between 1.5 and 1.6 in
Measured length: 1.54 in
The 1 and 5 are known with certainty
The last digit (4) is estimated between the two nearest fine division marks.

26. Example: Precision
Who is more precise when measuring the same 17.0 cm book? A:
17.0 cm, 16.0 cm, 18.0 cm, 15.0 cm
B ::
15.5 cm, 15.0 cm, 15.2 cm, 15.3 cm

27. Accuracy vs. Precision High Accuracy High Precision High Precision
Low Accuracy

28. The person hit the bull's-eye?
Three targets with three arrows each to shoot.
Precise but not accurate
Both accurate and precise
Neither accurate nor precise
How do they compare?
Can you define accuracy vs. precision?

29. Uncertainty
The word uncertainty casts a doubt about the exactness of the measurement results
True value = Estimated value + Uncertainty

30. Performance of Instruments
All instrumentation systems are characterized by the system characteristics or system response
There are two basic characteristics of Measuring instruments, they are
Static character
Dynamic character

31. Static Characteristics
The instruments, which are used to measure the quantities which are slowly varying with time or mostly constant, i.e., do not vary with time, is called ‘static characteristics’.

32. STATIC CHARACTERISTICS OF AN INSTRUMENTS
Accuracy
Precision
Sensitivity
Resolution
Threshold
Drift
Error
Repeatability
Reproducibility
Dead zone
Backlash
True value
Hysteresis
Linearity
Range or Span
Bias
Tolerance
Stability

33. Resolution
This is defined as the smallest input increment change that gives some small but definite numerical change in the output.

34. Threshold
This minimum value of input below which no output can be appeared is known as threshold of the instrument.
Output
input

35. Drift
Drift or Zero drift is variation in the output of an instrument which is not caused by any change in the input; it is commonly caused by internal temperature changes and component instability.
Sensitivity drift defines the amount by which instrument’s sensitivity varies as ambient conditions change.

36. Output
Output
sensitivity drift
zero drift
input
input
sensitivity drift
Output
zero drift
input

37. Error – The deviation of the true value from the desired value is called Error
Repeatability – It is the closeness value of same output for same input under same operating condition
Reproducibility - It is the closeness value of same output for same input under same operating condition over a period of time

38. Range
The ‘Range’ is the total range of values which an instrument is capable of measuring.

39. Hysteresis
This is the algebraic difference between the average errors at corresponding points of measurement when approached from opposite directions, i.e. increasing as opposed to decreasing values of the input.
Actual/ Input Value
Measured Value
Ideal
Hysteresis is caused by energy storage/ dissipation in the system.

40. Dead band
This is the range of different input values over which there is no change in output value.

41. Linearity- The ability to reproduce the input characteristics symmetrically and linearly

42. Backlash – Lost motion or free play of mechanical elements are known as backlash
True value – The errorless value of measured variable is known as true value
Bias – The Constant Error
Tolerance- Maximum Allowable error in Measurement

43. Dynamic Characteristics
The set of criteria defined for the instruments, which are changes rapidly with time, is called ‘dynamic characteristics’.

44. Dynamic Characteristics
Steady state periodic
Transient
Speed of response
Measuring lag
Fidelity
Dynamic error

45. Steady state periodic – Magnitude has a definite repeating time cycle
Transient – Magnitude whose output does not have definite repeating time cycle
Speed of response- System responds to changes in the measured quantity

46. Measuring lag
Retardation type :Begins immediately after the change in measured quantity
Time delay lag : Begins after a dead time after the application of the input
Fidelity- The degree to which a measurement system indicates changes in the measured quantity without error
Dynamic error- Difference between the true value of the quantity changing with time & the value indicated by the measurement system