Lecture#1

1

Measurement and Instrumentation

Lecture#1

Engr. M.Ubaidullah

2

Course Outline:

1. Basics Concepts

2. Essentials of Analog Instruments

3. Galvanometers, Ammeters & Voltmeters

4. Watt meters & Energy meters

5. Measurement of Resistance

6. Measurement of Inductance and Capacitance (AC Bridges)

7. Misc. Electrical Instruments

8. Electronics Instruments

9. Transducers

3

Reference Books:

Berlin, Electronic Instruments & Measurements

Modern Electronic Instrumentation & Measurement Techniques – A.D. Hell Frick and W.D Cooper.

Electronic Instrumentation & Measurements - David A Bell

A course in Electronic and electrical measurements and Instrumentation by J.B. Gupta

4

Objective of the Course:

5

Grading Scheme:

Assignments 3-4 10% Quizzes 3-4 10% Presentations 1-2 5% Midterm 25% Final Term 50%

6

1.Basics Concepts

1.1 Measurement Methods

1.2 Type of Measurement

1.3 Instruments

1.4 Classification of Instrumentations.

1.5 Terms related to measurement

1.6 Errors in measurement

1.7 Types of errors

7

Electronics:

Deals with motion of electrons

8

Measurement:

man uses his imaginative skills to identify a physical phenomena

Developed & utilized a means to understand this.

9

By measurement of a quantity, we mean “an act of comparison”

10

Instrumentation:

Deals with Science and technology of measurement of large no. of variablesUses principles in physics , chemistry & Appld. Science (Engg), Electrical. Electronics, Mech,computer, commn. etc.

11


Direct Comparison method:• Mostly used method• Unknown quantities are measured with z• comparison of known standards, e.g. length, mass etc• This is not very accurate method, as human errors are involved.

Indirect Comparison method:• More accurate than Direct method• More sensitive• Quantity is converted in analog form• Analog signal is processed and fed to the measuring instrument• The device which converts the quantity into suitable form is

called transducer.

12


13


Indirect Comparison method:• Amplification of the weak signal before giving it to the

measurement.

14


Primary Measurements: Direct measurement with comparison of respective standard. Needs no conversion in the measuring data. E.g. length, time, mass etc

Secondary Measurements: Needs one conversion. E.g. to measure pressure, 1st it will be converted into suitable

form by a transducer then fed into the instrument.

15


Tertiary Measurements: Needs two conversions. E.g. temperature measurement by thermocouples, involves

1st temperature conversion into voltage and then 2nd conversion into some readable form through a meter.

16


Tertiary Measurements: Needs two conversions. E.g. temperature measurement by thermocouples, involves

1st temperature conversion into voltage and then 2nd conversion into some readable form through a meter.

17

1.3 Instruments

An instrumentation may be defined as a device which helps

to determine value of an unknown quantity.

18


(A) Mechanical instruments.

Used to measure static and stable quantities.

E.g. force, pressure etc They cant measure

dynamic and variable quantities.

E.g. are pressure gauge, speedometer, water meter

Tire pressure gauge

19


(A) Electrical Instruments.

Faster than mechanical instruments However, their measuring part is also mechanical like

needle, springs etc They are more accurate and sensitive They can measure dynamic quantities like current (varying

at the rate of 50Hz/sec) measuring by ammeter. E.g. are ammeters, voltmeters etc

20


(A) Electronic Instruments.

Modern than the previous 2 types. Uses semiconductor devices like diodes, transistors etc

which have excellent time response and have no noise pollution.

E.g. are CRO, Power supplies etc.

21


(B) Instruments can also be classified as:

Absolute instruments. Secondary Instruments.

Analog instruments Digital Instruments

22


(B) Absolute instruments.

Which gives measurement quantity in terms of constant of the instrument.

Used in the laboratory for calibration and standardization. E.g. Tangent galvanometer

Secondary Instruments. Gives the measurement of the quantity directly on the

instrument. E.g. frequency meter, ohm meter, volt meter etc

23


(B) Secondary Instruments.

Analog instruments. Measure analog signals. E.g. temperature

Digital Instruments. Gives the digital measurement like DMM Also measure the analog signal.

24


Errors in analog instruments:

Parallax errorWhile taking reading, eye and pointer should be in

the same line, otherwise error occurs, called parallax error.

This error cant be removed completely. Human error

Reading wrongly or recorded wrongly.Parallax is also a type of human error.

25


Instrumentations can also be classified as: Indicating Instruments

Indicating instruments indicate, generally the quantity to be measured by means of a pointer which moves on a scale. Examples are ammeter, voltmeter, wattmeter etc.

Recording InstrumentsThese instruments record continuously the

variation of any electrical quantity with respect to time. In principle, these are indicating instruments but so arranged that a permanent continuous record of the indication is made on a chart or dial. Integrating instruments

26


Integrating instruments. These instruments record the consumption of

the total quantity of electricity, energy etc., during a particular period of time.

That is, these instruments totalize events over a specified period of time. No indication of the rate or variation or the amount at a particular instant are available from them.

Some widely used integrating instruments are: Ampere-hour meter: kilowatt-hour (kWh) meter, kilovolt-ampere-hour(kVARh) meter.

27


Instrument. Device to measure the value

True Value. The true or expected value of a quantity to be measured may be

defined as the average of an infinite number of measured values when the average deviation due to the various contributing factors tends to zero.

It also refers to a value of the quantity under consideration that would be obtained by a method (known as exemplar method) agreed upon by experts.

In other words, it is the most probable value that calculations indicate and one should expect to measure. Note that the value of the unknown obtained by making use of primary standards and measuring instruments is considered to be its true value.

28


Error. it is the deviation of the measured (or indicated) value from

the true (or expected) value of a quantity. In other words, error is the difference between the measured

value and the true value of the unknown quantity. It is also called absolute error are maximum possible error.

Then error of measurements is given by ∈A = Am – At ---------(1)

where Am = measured value of the quantityAt = true value of the quantity

29


Accuracy. Closeness of readings to the true value It is expresses as %age of true value.

Precision. It is measure of the consistency of reproducibility (repeatability) of

the measurement (i.e., the successive reading do not differ). For a given fixed value of an input variable, precision is a measure

of the degree to which successive measurement differ from one another.

30


Sensitivity.It is defined by the change in the output or response of the instrument for a unit change of input or measured variable.

Efficiency. Ratio of the measured quantity at full scale to the input

power taken by the instrument. Resolution or Discrimination.

Resolution is the smallest change in a measured variable (or measurand) to which the instrument will respond.

31


Fidelity. If the instrument produces the o/p exactly the replica of the input,

process is said to 100% fidelity. E.g. if a sine wave is fed to a CRO, the output of CRO should be

an exact sine wave without any distortion. Torque weight Ratio: (T/W)

Ratio of the deflecting torque produced on the moving system and weight of the moving system.

For accuracy this ratio should be less. Response speed and response time:

Rapid response of the instrument to the applied input. Time taken by the instrument to respond to the changes in the i/p.

32


1. Gross error

2. Systematic error

3. Random error

33


Gross error The class of error mainly covers human mistake in reading

instruments recording and calculating result. These can be avoided by two means :-

Great care should be taken with reading & recording the data.

2, 3 or more reading should be taker for the quantity under measurement.

some gross error can be detected & some others cannot. complete elimination is not possible.

34


Systematic error

There are divided as

Instrument Environmental Observational

35


Systematic error

These are divided as Instrumental error:

Due to inherent short comings in the instrument. Due to misuse of instrument. Due to loading effect of instrument. Cab be reduced by:

Substitution method or calibration against standard may be used for the purpose.

Correction factors should be applied after determining instrumental errors.

Instrument may be recalibrated carefully.

36


Systematic error There are divided as

Environmental due to surroundings E.g. Noise from

electrical machine. Magnetic field, temperature

Observational may be due to misreading of instruments.

37


Random Error: Errors due to unknown Causes. Magnitude and direction not known Expressed as average deviation of probable errors or

standard deviation Can be reduced by: Increasing the no. of readings and using

statically method.

38

Statistical Analysis:

Arithmetic Mean

39


Deviation from Mean

d1=x1- A.M.

d2=x2- A.M.

40


Average Deviation

D= |di| / n

41


Standard Deviation

= sqrt ( |d i| 2/ n)

For finite observations

= sqrt ( |d i| 2/ (n-1))

42


Variance

v= 2

43


Probable error

= +/- 0.6745

(obtained from Gaussian error curve)

44


Limiting error

specified by manufactures

45

Summary:



1.3 Instruments




1.7 Types of errors

Statistical Analysis

46

Lecture#1

Documents

measurement

measurement

absolute instruments

analog instruments

statistical

integrating

secondary

readable form