Analog Mode• Produce the signals that vary in continuous way. Infinite number of values

in any given range.

• Example: Analog Oscilloscope

Digital Mode- Produce the signals that vary in discrete steps.Finite different values in a

given range.

- Example : Digital Oscilloscope

Instrument ModelInstrument Model

Instrument Model …continuedInstrument Model …continued

•• Important element isImportant element is sensorsensor which canwhich canconvert the physical variable into signalconvert the physical variable into signalvariable.variable.

•• Signal variable can be displayed, recordedSignal variable can be displayed, recorded•• Signal variable can be displayed, recordedSignal variable can be displayed, recordedor integrated in the secondary instrumentor integrated in the secondary instrumentsystem.system.

•• Signal variable may also be used as anSignal variable may also be used as aninput signal of a control system.input signal of a control system.

Elements of ElectronicElements of ElectronicInstrumentation …continuedInstrumentation …continued

Source: [Dally1993] pg. 2Source: [Dally1993] pg. 2

Elements of ElectronicElements of ElectronicInstrumentationInstrumentation

•• TransducersTransducers–– Device that converts a change in physical quantityDevice that converts a change in physical quantity

into a change of a electric signal quantity.into a change of a electric signal quantity.

•• Power SupplyPower Supply•• Power SupplyPower Supply–– Provide energy to drive the transducers.Provide energy to drive the transducers.

•• Signal Conditioning CircuitsSignal Conditioning Circuits–– Electronic circuits that manipulate, convert theElectronic circuits that manipulate, convert the

output from transducers into more usableoutput from transducers into more usableelectrical signal.electrical signal.•• Eg. Filters, compensators, modulators, demodulators,Eg. Filters, compensators, modulators, demodulators,

integrators and differentiatorsintegrators and differentiators

Elements of ElectronicElements of ElectronicInstrumentation …continuedInstrumentation …continued

•• AmplifiersAmplifiers–– Amplify low voltage signal from transducers or signal conditioningAmplify low voltage signal from transducers or signal conditioning

circuit.circuit.

•• RecordersRecorders–– Used to display the measurement for easy reading andUsed to display the measurement for easy reading and–– Used to display the measurement for easy reading andUsed to display the measurement for easy reading and

interpretation.interpretation.•• Recorders can be analog or digital. The voltage from amplifier is anRecorders can be analog or digital. The voltage from amplifier is an

analog signal that is the input to recorder. Analog recorders, such asanalog signal that is the input to recorder. Analog recorders, such asOscilloscopes or magnetic tape display or store the analog signal.Oscilloscopes or magnetic tape display or store the analog signal.Digital recorders accept an analog input and convert this signal to aDigital recorders accept an analog input and convert this signal to adigital code that is then displayed in a numerical array or stored ondigital code that is then displayed in a numerical array or stored onmagnetic media.magnetic media.

•• Data ProcessorsData Processors–– Can be a microprocessor or microcontroller.Can be a microprocessor or microcontroller.

•• Incorporate analogIncorporate analog--toto--digital converters (A/D) and provide the outputdigital converters (A/D) and provide the outputsignal representing the measurement in digital code.signal representing the measurement in digital code.

Elements of ElectronicElements of ElectronicInstrumentation …continuedInstrumentation …continued

•• Process ControllersProcess Controllers–– Used to monitor and adjust any quantity at the specifiedUsed to monitor and adjust any quantity at the specified

level or value.level or value.•• Signal from instrumentation system is compared with aSignal from instrumentation system is compared with a

command signal that reflects the required value of thecommand signal that reflects the required value of thequantity in the process.quantity in the process.quantity in the process.quantity in the process.

•• The process controller accepts both the command signal andThe process controller accepts both the command signal andthe measured signal and forms the difference to give an errorthe measured signal and forms the difference to give an errorsignal. The error signal is automatically adjust the process.signal. The error signal is automatically adjust the process.

•• Command GeneratorCommand Generator–– Provide control voltage that represents the difference ofProvide control voltage that represents the difference of

the parameter in a given process.the parameter in a given process.•• Eg. The timeEg. The time--temperature profile for an oven must betemperature profile for an oven must be

controlled in curing plastics. The command generatorcontrolled in curing plastics. The command generatorprovides a voltage signal that varies with time in exactprovides a voltage signal that varies with time in exactproportion to the timeproportion to the time--temperature profile required of thetemperature profile required of thecuring oven.curing oven.

Areas of ApplicationAreas of Application

•• Engineering AnalysisEngineering Analysis–– To validate new design of structure, component orTo validate new design of structure, component or

system by theoretical and experimental approach.system by theoretical and experimental approach.

•• Process ControlProcess Control–– Monitoring processMonitoring process –– provide onprovide on--line (realline (real--time) datatime) data–– Monitoring processMonitoring process –– provide onprovide on--line (realline (real--time) datatime) data

that allow operator to response and makethat allow operator to response and makeadjustments to control the process.adjustments to control the process.

–– Automatic processAutomatic process –– provide onprovide on--line (realline (real--time)time)operating data that are used as feedback signal inoperating data that are used as feedback signal inclosedclosed--loop control systems to continuously controlloop control systems to continuously controlthe process.the process.

ContentsContents

•• InstrumentInstrument

•• Basic MeasurementBasic Measurement

–– Standard UnitsStandard Units–– Standard UnitsStandard Units

–– Errors in MeasurementErrors in Measurement

Basic MeasurementBasic Measurement

•• Measurement …definitionMeasurement …definition

–– Determination of magnitude of a given quantity byDetermination of magnitude of a given quantity bycomparison between quantity and standard value.comparison between quantity and standard value.

•• Measurement is a process of translating theMeasurement is a process of translating the•• Measurement is a process of translating theMeasurement is a process of translating thephysical parameters into numerical value.physical parameters into numerical value.

•• Numerical must accompanied with unit toNumerical must accompanied with unit toidentify the property and the characteristics ofidentify the property and the characteristics ofmeasurand.measurand.

Measurement MethodsMeasurement Methods•• Indirect MethodIndirect Method

–– Measurand is determined by measuring other functionally relatedMeasurand is determined by measuring other functionally relatedquantities and calculating the desired quantity.quantities and calculating the desired quantity.

–– Indirect measurement is a technique that is used when it is eitherIndirect measurement is a technique that is used when it is eitherdifficult or impossible to measure a quantity by direct methods.difficult or impossible to measure a quantity by direct methods.

–– ExamplesExamples

•• The volume of a rectangular prism (such as a shoebox) can be found quite easily byThe volume of a rectangular prism (such as a shoebox) can be found quite easily bymeasuring the length, width, and height, and then finding the product of thesemeasuring the length, width, and height, and then finding the product of theseamounts. A rectangular prism with dimensions of length 4 inches, 11 inches, and 6amounts. A rectangular prism with dimensions of length 4 inches, 11 inches, and 6amounts. A rectangular prism with dimensions of length 4 inches, 11 inches, and 6amounts. A rectangular prism with dimensions of length 4 inches, 11 inches, and 6inches has a volume of 4 in. x 11 in. x 6 in. = 264 in.3. An object that is not wellinches has a volume of 4 in. x 11 in. x 6 in. = 264 in.3. An object that is not welldefined, such as a rock, presents a problem because geometric formulas cannot bedefined, such as a rock, presents a problem because geometric formulas cannot beapplied. In such cases, indirect measurements must be used. One indirect method ofapplied. In such cases, indirect measurements must be used. One indirect method ofmeasurement is liquid displacement. Suppose you had an aquarium in the shape of ameasurement is liquid displacement. Suppose you had an aquarium in the shape of arectangular prism, with a base of length 15 inches and width 8 inches. You can placerectangular prism, with a base of length 15 inches and width 8 inches. You can placea rock of unknown volume in the water and measure how much the water rises. Ifa rock of unknown volume in the water and measure how much the water rises. Ifthe water rises inch, the volume of the rock is calculated asthe water rises inch, the volume of the rock is calculated as

15in. x 8in. x = 60 in.3.15in. x 8in. x = 60 in.3.

In other words, the volume of the rock is equal to the volume of water that isIn other words, the volume of the rock is equal to the volume of water that isdisplaced.displaced.

Indirect Method…Cont…Indirect Method…Cont…

Indirect MethodIndirect Method –– Resistance MeasurementResistance Measurement

Direct MethodDirect Method

•• Measurand is directly compared against a standard.Measurand is directly compared against a standard.Most widely used in engineering practice.Most widely used in engineering practice.

•• Example : Measurement of temperature withExample : Measurement of temperature with•• Example : Measurement of temperature withExample : Measurement of temperature withthermocouplethermocouple

ContentsContents

•• InstrumentInstrument

•• Basic MeasurementBasic Measurement

–– Standard UnitsStandard Units–– Standard UnitsStandard Units

–– Errors in MeasurementErrors in Measurement

Standard UnitsStandard Units

•• The International System of Units (SI)The International System of Units (SI)

•• Base unitsBase units

–– LengthLength –– meter (m)meter (m)

–– MassMass –– kilogram (kg)kilogram (kg)–– MassMass –– kilogram (kg)kilogram (kg)

–– TimeTime –– second (s)second (s)

–– Electric currentElectric current –– ampere (A)ampere (A)

–– TemperatureTemperature –– kelvin (K)kelvin (K)

–– Luminous intensityLuminous intensity –– candela (cd)candela (cd)

–– Amount of substanceAmount of substance –– mole (mol)mole (mol)

Standard Units …continuedStandard Units …continued

•• Derived unitsDerived units–– Electric chargeElectric charge –– coulomb (C)coulomb (C)

–– Electric potential differenceElectric potential difference –– volt (V)volt (V)

–– Electric resistanceElectric resistance –– ohm (ohm (ΩΩ))–– Electric resistanceElectric resistance –– ohm (ohm (ΩΩ))

–– Electric capacitanceElectric capacitance –– farad (F)farad (F)

–– Electric inductanceElectric inductance –– henry (H)henry (H)

–– EnergyEnergy –– joule (J)joule (J)

–– ForceForce –– newton (N)newton (N)

–– Magnetic fluxMagnetic flux –– weber (Wb)weber (Wb)

–– PowerPower –– watt (W)watt (W)

ContentsContents

•• InstrumentInstrument

•• Basic MeasurementBasic Measurement

–– Standard UnitsStandard Units–– Standard UnitsStandard Units

–– Errors in MeasurementErrors in Measurement

STATIC CHARACTERISTICSTATIC CHARACTERISTIC

•• AccuracyAccuracy –– The degree of exactness (closeness) of a measurementThe degree of exactness (closeness) of a measurementcompared to the expected (desired) valuecompared to the expected (desired) value

•• ResolutionResolution –– The smallest change in a measured variable to which anThe smallest change in a measured variable to which aninstrument will respondinstrument will respond

•••••••• PrecisionPrecision –– A measure of the consistency or repeatability of measurementsA measure of the consistency or repeatability of measurements

•• Expected ValueExpected Value –– The design value; i.e The most probable value thatThe design value; i.e The most probable value thatcalculations indicate one should expect to measurecalculations indicate one should expect to measure

•• ErrorError –– The deviation of the true value from the desired value.The deviation of the true value from the desired value.

•• SensitivitySensitivity –– The ratio of the change in output (response) of the instrumentThe ratio of the change in output (response) of the instrumentto a change of input or measured variableto a change of input or measured variable

Errors in MeasurementErrors in Measurement

•• Deviation of measurand value from trueDeviation of measurand value from truevalue.value.

•• Usually expressed in percentage.Usually expressed in percentage.•• Usually expressed in percentage.Usually expressed in percentage.

•• Broadly defined in three categories;Broadly defined in three categories;

–– Gross errorsGross errors

–– Systematic errorsSystematic errors

–– Random errorsRandom errors

Gross ErrorsGross Errors

•• Errors occur because of the humanErrors occur because of the humanmistakes.mistakes.

–– Improper or incorrect installation ofImproper or incorrect installation of–– Improper or incorrect installation ofImproper or incorrect installation ofmeasurement instrument.measurement instrument.

–– Failure to eliminate parallax during reading orFailure to eliminate parallax during reading orrecording the measurement.recording the measurement.

–– Cannot be remedied mathematically.Cannot be remedied mathematically.

Systematic errorsSystematic errors

•• Errors occur constantlyErrors occur constantly•• Two types of systematic errors;Two types of systematic errors;

–– Instrumental errorsInstrumental errors•• Inherent in the instrument due to their mechanical structure, calibrationInherent in the instrument due to their mechanical structure, calibration

or operation.or operation.

–– Environmental errorsEnvironmental errors••

–– Environmental errorsEnvironmental errors•• Unpredictable due to the using an instrument at different locations orUnpredictable due to the using an instrument at different locations or

conditions.conditions.

–– Observational ErrorsObservational Errors•• Introduced by the observer and estimation when obtaining a readingIntroduced by the observer and estimation when obtaining a reading

from a meter scale.from a meter scale.

•• Systematic errors divided into static and dynamic errorsSystematic errors divided into static and dynamic errors–– Static errorsStatic errors

•• caused by limitations of the measuring device or the physical lawscaused by limitations of the measuring device or the physical lawsgoverning its behaviourgoverning its behaviour

–– Dynamic errorsDynamic errors•• Caused by the instrument not responding fast enough to follow theCaused by the instrument not responding fast enough to follow the

changes in a measured variablechanges in a measured variable

Random errorsRandom errors

•• Occur when different results in magnitudeOccur when different results in magnitudeor sign obtained on repeatedor sign obtained on repeatedmeasurement of one or the samemeasurement of one or the samequantity.quantity.quantity.quantity.

•• The effect can be minimised by taking theThe effect can be minimised by taking themeasurement many times.measurement many times.

•• This error can be handle mathematically.This error can be handle mathematically.

Error in MeasurementError in Measurement

•• Error may be expressed either as absolute or as percentage of error.Error may be expressed either as absolute or as percentage of error.

•• Absolute error defined as the difference between the expected value ofAbsolute error defined as the difference between the expected value ofthe variable and the measured value of the variable.the variable and the measured value of the variable.

•• Formula:Formula:

XnYne

100%

,,

xvalueExpected

valueabsoluteError

valuemeasuredXnvalueExpectedYnerrorabsolutee

XnYne

Yn

XnYnA

AAccuracyrelative

1

,

%100

%%100

),(%

Aa

errora

aAccuracy

Eg.1.1Eg.1.1

The expected value of the voltage across a resistor is80V. However, the measurement gives a value of 79V.Calculate:(i) absolute error(i) absolute error(ii) % error(iii) relative accuracy(iv) % of accuracy

Solution 1.1Solution 1.1

XnYne

7980

9875.0

80

798011

Yn

XnYnA

(i) Absolute error, (iii) Relative Accuracy,

V1

%25.1

10080

7980

100%

x

xYn

XnYnerror

(ii) % error,(iv) % of Accuracy,

%75.98

%25.1%100%%100

%75.989875.0100100

errorofa

xAxa

Solution 1.3Solution 1.3

kmAI

VR

T

TT 8

10

80(i) The total circuit resistance, RT

(iI) The voltmeter resistance equals, RV

kxVRV 150150/1000

kk

k

kk

kxk

RR

RxRR

TV

VTx 45.8

142

1200

8150

1508 2

(iI) The voltmeter resistance equals, RV

(iii) % error, (Actual value – Apparent value)/Actual value

actual value of unknown resistance, Rx

%3.5100053.010045.8

845.8

xx

k

kk

Solution 1.3 (Cont…)Solution 1.3 (Cont…)

506.0

30

T

TT

I

VR

kxVRV 150150/1000

(i) The total circuit resistance is given by,

(ii) The voltmeter resistance RV equals

167.50

5.149

7500

50150

15050

k

k

k

kx

RR

RxRR

TV

VTx

Neglecting the resistance of the mili-ammeter,the value of unknown resistance = 50

%33.0

100167.50

167.0

100167.50

50167.50%

x

xerror