1. principles of measurement

These slides describes the deifintion of measurement, Classification of instruments and methods of measurement.

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1. Introduction
•Principles of Measurement
•Classification of instruments
•Methods of measurement

2. Principles of Measurement
What is Measurement?
•Measurement tell us about property of something.
•Measurement provide us with a means of describing
various phenomena in quantitative terms.
•Measurement is the process by which one can
convert physical parameter to meaningful numbers.
•Measurement are always made by using an
instrument (tool) of some kind. (Example: Ruler,
Thermometer, Stop watch, Weighing machines)
•Measurement gives a number to that property.

3. Principles of Measurement
What is Measurement?
Result of measurement contains two parts
i) Unit of measurement
ii) Number

4. Principles of Measurement
What is Measurement?
Measurement is the act or the result of a quantitative
comparison between the quantity (whose magnitude is
unknown) and a predefined standard.
Measurand: Physical parameter or variable to be
measure.
Standard: A quantity of the same kind chosen as a
unit or basis for comparison of quantitative value to
measure.

5. Principles of Measurement
BASIC REQUIREMENTS OF MEASUREMENT
•The standard used for comparison purposes must be
accurately defined & should be commonly accepted
•The standard must be of the same character as the
measurand
•The apparatus used & the method adopted must be
provable.

6. Principles of Measurement
MEASURINGINSTRUMENT:
It may be defined as a device for determining the v alue or
magnitude of a quantity or variable.
Electronic instrument :
•An electronic instrument is the one which is based on
electronic or electrical principles for its measurement
function.
•Themeasurementofanyelectronicorelectricalquantityor
variableistermedasanelectronicmeasurement.

7. Principles of Measurement
Advantages of Electronic Measurement :
1.
Most of the quantities can be converted by transducers
intotheelectricalorelectronicsignals.
2. An electrical or electronic signal can be amplified,
filtered,multiplexed,sampledandmeasured.
3. The measurement can easily be obtained in or converted
intodigitalformforautomaticanalysisandrecording.
4. The measured signals can be transmitted over long
distances with the help of cables or radio links, without any
lossofinformation.
5. Electronic circuits can detect and amplify very weak
signalsandcanmeasuretheeventsofveryshortdurationas
well.

8. Principles of Measurement
FUNCTIONAL ELEMENTS OF AN INSTRUMENT
Most of the measurement systems contain three main functional ele ments. They are:
i) Primary sensing element
ii) Variable conversion element
iii) Data presentation element.

9. Principles of Measurement
FUNCTIONAL ELEMENTS OF AN INSTRUMENT
•Primary sensing element:which senses thequantity under
measurement
•Variable conversion element:which modifies suitably the output of
the primary sensing element
•Variable Manipulation Element:The signal gets manipulated here
preserving the original natureof it
•Data Transmission Element:The transmission of data from one
another is done by the datatransmission element
•Data presentation element: The display or readout devices which
display the required informationabout themeasurement.

10. Principles of Measurement Just take an example of analoguemeter used to
measure current (Ammeter), all necessary
elements are shown in blockdiagram.

11. Classification of Instruments
Instruments can classified into many
categories, one classification is given as under.
1.
Active/Passiveinstruments
2.
Null or deflectiontype
3.
Monitoring or controltype
4.
Analogue ordigital
5.
Absolute orsecondary

12. 1.
Active/Passive
Passive Instruments: (Easy design,cheap)
•In which the output is produced completely
by the quantity that is measured.
•An example of a passive instrument is the
pressure measuring device. The pressure of
the fluid is translated into movement of a
pointeragainstascale.Theenergyexpended
in moving the pointer is derived entirely
fromthe change in pressure measured; there
arenootherenergyinputstothesystem.

13. ActiveInstruments:(Difficulttodesign, costly)
Inwhichthequantitybeingmeasured activatesthe
magnitude of some external power input source,
whichinturnproducesthe measurement. Example:Float-typepetrol-tanklevelindicator
•Changeinpetrollevelmoves a potentiometerarm
•Outputsignalconsistsof a
proportionof theexternalvoltagesource.
•Theenergyintheoutputsignal
comes fromtheexternalpower source.
•The primary transducer float system is merely modulating
thevalueof thevoltagefromthisexternalpower source.

14. 2.
Null/Deflection
Nulltypeinstruments:
In which a zero or null indication leads to the
determination of magnitude of the quantity being
measured.
Example:DC potentiometer,WheatstoneBridge
Deflectiontype instrument:
In which the quantity being measured produces some
effect dueto whichpointer deflects.
Example:PMMC instrument.

15. 3.
Monitoring /Control
Monitoring typeinstruments:
In which some indication or condition of
parameter value under study is obtained.
Example: All deflection type or digital instruments
Control type instruments:
These are used in automatic control systems in the
feedback path, to send a feedback signal from the
output of a process to its input.
Example: Automatic air-conditioning system.

16. 4.
Analogue/digital
Analoguetypeinstruments:
In which output varies in continuous fashion as quantity
beingmeasured, havinginfinite valuesinagiven range.
Example: Deflecting Instruments are good examples of
analogue instruments.
DigitalInstruments:
In which output varies in discrete step and
thus give finite values in a given range.
Example: DigitalMulti-meter

17. 5.
Absolute/Secondary
AbsoluteInstruments:
In which magnitude of quantity is measured in terms of
physicalconstantsof the instrument.
Example:Tangentgalvanometer
Secondarytypeinstruments:
In which the reading shown by the instrument gives
directly the measurement of the quantity being
measured.
Example: Voltmeter, ammeter, wattmeter.

18. There are two methods ofmeasurement. 1.
Directmeasurement
2.
IndirectMeasurement
DirectMeasurement:
Indirectmeasurementthequantitybeing measured
produce certain effect which gives the indication
onmeter.
Example:Measurementofcurrentbyammeter.

19. Direct methods are classifiedas 1.
Deflectionmethods
2.
Comparisonmethods
“Deflection
pointer on
measured.
method”includes the deflection of
a scale due to the quantity to be
Example: Wattmeter, ammeter voltmeter
“Comparison method”include the comparison of the
quantity under measurement with a pre-defined standard
quantitywhichgives measurement.
Example: potentiometer.

20. Indirectmeasurement:
In which the quantity to be measured is not measur ed directly,
but other parameter related to the quantity are mea sured.
Example 1:
For measurement of power (P) we measurevoltage
(V) and current (I) then P = V*I
Example 2:
For measurement of resistance (R) we measure (V) a nd current
(I) then R=V/I