1. ELECTRONIC INSTRUMENTATION(EC010704)
SNGCE
ELECTRONIC INSTRUMENTATION(EC010704)
Reference Books
Measurement System : Ernest O Doebelin
Electronic Instrumentation : H.S Kalsi
DEEPAK P

2. Electronic Instrumentation
SNGCE
Electronic Instrumentation
Instrumentation is a branch of engineering that deals with the measurement and control of different parameters. or
Instrumentation is defined as "the art and science of measurement and control". 
Measuring is used to monitor a process or operation
DEEPAK P

3. Engineering Measurement
SNGCE
UNIT 1
Objectives of
Engineering Measurement
DEEPAK P

4. Objectives At the end of this Unit Basic measuring system
Performance characteristics of instruments
Errors in measurement
Units-Dimensions Standards.
Instrument calibration.

5. Objectives Of Engineering Measurements
SNGCE
Objectives Of Engineering Measurements
Measurements of system parameter information.
Automatic control of a system.
Simulation.
Experimental design.
To perform various manipulation.
Testing of materials and quality control.
Verification of scientific theories.
DEEPAK P

6. Basic Measuring System
SNGCE
Basic Measuring System
A measurement assigns a specific value to a physical variable. The physical variable now becomes the measured variable.
A measurement system is a tool used to measure the physical variable.
Methods of measurement can be classified in to two
Direct methods
Un known quantity is directly compared against a standard
Result is expressed as a numerical number
In direct methods
In engineering application measurement systems uses this methods
DEEPAK P

7. Simple measuring system
SNGCE
Simple measuring system
Signal conditioning element
Data trans element
Data processing element
Primary sensing element
Transducer
Data display
Data recording
DEEPAK P

8. Basic Measuring System
SNGCE
Basic Measuring System
Four Parts of Measurement System
Sensor-Transducer Stage
Signal Conditioning Stage
Output Stage
DEEPAK P

9. SNGCE
Sensor
The sensor is a physical element that uses some natural phenomenon to sense the variable being measured.
The transducer changes this sensed information into a detectable signal form (electrical, mechanical, optical, etc.)
A Transducer is a device which converts one form of energy into some other form of energy
It is also known as 'Pickup Element'.
DEEPAK P

10. SNGCE
Sensor
Mainly Transducers can be classified into two types on the basis of power supply required
Active Transducers
Passive Transducers.
Active transducers are those which does not requires external power supply for their operation.
For example: Photo Voltage Cell, Piezo Electric Crystal, Generator etc.
Passive Transducers: Passive Transducers are those transducers which requires external power supply for their operation.
For Example: Resistive, Inductive and Capacitive Transducers.
DEEPAK P

11. SNGCE
Signal Conditioner
Its role comes into play when the output of transducer or primary sensing element is very low. It is used to amplify or modify the incoming signal from transducer according to output requirement.
When noise is present in signal, filters need to be used to eliminate it.
If the processor operates only on digital signal, A/D and D/A converters must be used at the input and output of the processor
In other words Signal Conditioning is done to improve the quality of output of measurement system.
DEEPAK P

12. SNGCE
Signal Conditioner
This optional intermediate stage can be used to increase
The magnitude of the signal through amplification,
Remove portions of the signal through some filtering technique,
Provide mechanical or optical linkage between the transducer and the output range.
DEEPAK P

13. SNGCE
O/P stage
The output unit of a measurement system is consists of a display and storage unit
It is used to display or analyze the final output of the measurement system.
The examples of Output unit can be any output device like CRO (Cathode Ray Oscilloscope) or XY recorder.
DEEPAK P

14. Comparison Digital Signal Analog Signal
Data Storage can be easily done
Processing of digital information is very easy
Will not interfere with other signals, so less affected with Noise. Data transmission quality is good
Repeaters are required for long distance communication
Difficult to store the signal/information
Processing of signal is difficult
Will interfere with other signals, so affected with noise. Transmission quality is comparatively poor
Repeaters are not required

15. Performance characteristics of instruments
SNGCE
Performance characteristics of instruments
JOBY JOHN
DEEPAK P

16. Performance characteristics of instruments
SNGCE
Performance characteristics of instruments
A knowledge of the performance characteristics of an instrument is essential for selecting the most suitable instrument for specific measuring jobs.
Performance characteristics of an instrument are mainly divided into two.
Static characteristics
Dynamic characteristics
DEEPAK P

17. STATIC CHARACTERISTICS
SNGCE
STATIC CHARACTERISTICS
The set of criteria defined for the instrument which are used to measure the quantities that are varying slowly with time or constant is called static characteristics. OR
The static characteristics of an instrument are considered for instruments which are used to measure an unvarying process condition.
Some criteria will be set to for the measurement of quantities that are either constant or vary slowly is called static characteristics
DEEPAK P

18. STATIC CHARACTERISTICS
SNGCE
STATIC CHARACTERISTICS
All the static performance characteristics are obtained by one form or another of a process called calibration.
It provides a opportunity to check the instrument against a known standard and to find the errors and accuracy.
Calibration involves comparison of an instrument with either primary standard or a secondary standard or an instrument with known accuracy
DEEPAK P

19. STATIC CHARACTERISTICS
SNGCE
STATIC CHARACTERISTICS
There are a number of related definitions (or characteristics) such as
Accuracy & Precision
Sensitivity
Linearity & Hysteresis
Repeatability and Reproducibility
Resolution, 
Drift,
Span
Threshold etc.
DEEPAK P

20. STATIC CHARACTERISTICS
SNGCE
STATIC CHARACTERISTICS
Accuracy: The degree of exactness (closeness) of a measurement compared to the expected (true) value.
It is expressed in terms of errors
Static error = measured value – true value
Precision: A measure of the consistency or reproducibility of measurements, i.e. successive readings does not differ.
(Precision is the consistency of the instrument output for a given value of input).
Accuracy can be improved by calibration but not precision
DEEPAK P

21. STATIC CHARACTERISTICS
SNGCE
STATIC CHARACTERISTICS
Resolution: The smallest change in a measured variable to which an instrument will respond.
Sensitivity: The ratio of the change in output (response) of the instrument to a change of input or measured variable.
Drift : Gradual shift in the meassured value ,over an extended period, when there is no change in input.
Threshold: The minimum value of input for which the device just starts to respond
Range/Span: The minimum and maximum value of quantity so that the device is capable of measuring
DEEPAK P

22. STATIC CHARACTERISTICS
SNGCE
STATIC CHARACTERISTICS
Repeatability: A measure of how well the output returns to a given value when the same precise input is applied several times. Or
The ability of an instrument to reproduce a certain set of reading within a given accuracy.
DEEPAK P

23. Linearity Input output relationship of a device must be linear
SNGCE
Linearity
Input output relationship of a device must be linear
i.e, Y= mx +C
But practical systems shows small deviations from the linear shape ( allowed within the specified limits)
DEEPAK P

24. Hysteresis
Input is increased from negative value, output increases as indicated by curve 1
Then the input is steadily decreased , output does not follow the same path , but lag by a certain value as indicated by curve 2
The difference between the two curves is called Hysterisis
JOBY JOHN

25. DYNAMIC CHARACTERISTICS
SNGCE
DYNAMIC CHARACTERISTICS
The response of instruments or systems to dynamic I/P s are also functions of time.
Instruments rarely respond instantaneously to changes in the measured variables
Instead, they exhibit slowness or sluggishness due to such things as mass, thermal capacitance, fluid capacitance or electric capacitance
DEEPAK P

26. DYNAMIC CHARACTERISTICS
SNGCE
DYNAMIC CHARACTERISTICS
The dynamic characteristics of an instrument are
Speed of response
Fidelity
Time delay or lag
Dynamic error
DEEPAK P

27. DYNAMIC CHARACTERISTICS
SNGCE
DYNAMIC CHARACTERISTICS
Speed of Response:
It is the ability of a system to respond to a sudden changes in the input signal/quantity
Fidelity:
It is the degree to which an instrument indicates the changes in the measured variable without dynamic error ( Indication of how much faithfully system responds to the changes in input).
DEEPAK P

28. DYNAMIC CHARACTERISTICS
SNGCE
DYNAMIC CHARACTERISTICS
Lag:
It is the retardation or delay in the response of an instrument to changes in the measured variable.
Two types : Process lag(process) and Control lag (Instrument)
Dynamic Error:
It is the difference between the true values of a quantity changing with time and the value indicated by the instrument, if no static error is assumed.
NOTE : The dynamic and transient behavior of the instrument is as important as the static behavior.
DEEPAK P

29. DYNAMIC CHARACTERISTICS
Inputs used to study characteristics of a system are
Impulse signal
Step Signal
Ramp signal
Exponential signal (sinusoidal signal)
Transient Response
Response exhibited by the system suddenly after an input change
Steady State response
Response exhibited by the system at infinite time after an input change

30. Time Response of a System
Peak Time
Time taken to reach the maximum overshoot
Delay Time
Time taken to reach 50% of the final expected value at the first time
Time constant
Time required to for the output to reach 63.2% of its final value
Settling Time
Time taken for the output oscillations are died out completely or diminished within the allowed limits
Rise Time
Time taken by the system to reach the desired value first time in the transient stage, when the input is changed from one state to another
Over shoot
Maximum deviation of the output from input in the transient stage.
Percentage of overshoot = (Max. Overshoot/ Final expected value)*100

31. Time Response of a System
JOBY JOHN

32. SNGCE
Error
JOBY JOHN
DEEPAK P

33. SNGCE
Error
Error is the difference between the true value of the variable and the measured value.
Errors are classified as
Gross error /Human error (human mistakes and instrument malfunctions)
Random errors (Noise/Interference)
Systematic errors (which may be either constant or variable)-Due to shortcoming of the instruments
DEEPAK P

34. Random Errors
Associated to any measurement or electronic signal we find random, non-deterministic variations as the result of different sources:
Electronic noise (Johnson, shot,..)
Interference
Even though interference is systematic ,for the easiness of modeling, it can be rendered as random.
All the random sources are independent.
JOBY JOHN

35. Gross error Instrumentation misuse, calculation errors and
SNGCE
Gross error
Instrumentation misuse, calculation errors and
other human mistakes (mistakes in reading, recording )are the main source of Gross errors.
Gross error mainly occur due to carelessness or lack of experience of a human being or incorrect adjustments of instruments
These errors can be minimized by
1.Taking great care while taking reading, recordings and calculating results.
2. Taking multiple readings preferably by different persons.
DEEPAK P

36. SNGCE
Systematic errors
A constant uniform deviation in the operation of an instrument is known as systematic error.
There are three types of systematic errors as
Instrumental errors
Environmental errors
Observational errors
DEEPAK P

37. Systematic Errors Instrumental errors
SNGCE
Systematic Errors
 Instrumental errors
These errors are mainly due to following three reasons
Short-comings of instrument
These are because of the mechanical structure of the instruments eg. Friction in the bearings of various moving parts, irregular spring tensions, hysteresis, gear backlash, variation in air gap etc.
Ellimination.
Selecting proper instrument and the transducer for the measurement.
Recognize the effect of such errors and apply the proper correction factors.
Calibrate the instrument carefully against standard.
DEEPAK P

38. Systematic errors INSTRUMENTAL ERRORS Misuse of instrument
SNGCE
Systematic errors
  INSTRUMENTAL ERRORS
Misuse of instrument
  A good instrument if used in abnormal way gives misleading results.
Poor initial adjustments,
Improper zero setting,
Using leads of high resistance.
Elimination: Use the instrument intelligently & Correctly
 Loading effects
Loading effects due to
Improper way of using the instrument
DEEPAK P

39. Systematic Errors Observational Errors
SNGCE
Systematic Errors
  Observational Errors
Error introduced by the observer
Few souces are:
Parallax error while reading the meter,
wrong scale selection,
habits of individual obsever
Elimination
Use the
instrument with mirrors,
instrument with knife edge pointers,
Instrument having digital display
DEEPAK P

40. Systematic Errors
Environmental Errors (due to the External Conditions)
The various factors : Temperature changes, Pressure, vibratons, Thermal emf., stray capacitance, cross capacitance, effect of External fields, Aging of equipments and Frequency sensitivity of an instrument.
Elimination
Using proper correction factors and using the instrument Catalogue
Using Temperature & Pressure control methods etc.
Reducing the effect of dust, humidity on the components in the instruments.
The effects of external fields can be minimized by using the magnetic or electrostatic shields of screens.

41. Error due to Other Factors
SNGCE
Error due to Other Factors
Effect of the Time on Instruments
There is a possibility of change in calibration error in the instrument with time. This may be called ageing of the instrument.
Mechanical Error
Friction between stationary and rotating parts and residual torsion in suspension wire cause errors in instruments. So, checking should be applied. Generally, these errors may be checked from time to time.
DEEPAK P