mecn 4600 inter - bayamon lecture 9 mechanical measurement and instrumentation mecn 4600 professor:...

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LectureLecture

99Mechanical Measurement and Mechanical Measurement and

InstrumentationInstrumentation MECN 4600 MECN 4600

Professor: Dr. Omar E. Meza CastilloProfessor: Dr. Omar E. Meza [email protected]

http://www.bc.inter.edu/facultad/omeza

Department of Mechanical EngineeringDepartment of Mechanical Engineering

Inter American University of Puerto RicoInter American University of Puerto Rico

Bayamon CampusBayamon Campus

Lecture 9Lecture 9MEC

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Tentative Lecture ScheduleTentative Lecture Schedule

TopicTopic LectureLecture

Basic Principles of MeasurementsBasic Principles of MeasurementsResponse of Measuring Systems, System DynamicsResponse of Measuring Systems, System DynamicsError & Uncertainty AnalysisError & Uncertainty Analysis

1, 2 and 31, 2 and 3

Sensor & TransducersSensor & TransducersBasic Electronics, Signal ProcessingBasic Electronics, Signal Processing

44

Measurement of PressureMeasurement of Pressure 55

Measurement of TemperatureMeasurement of Temperature 6, 7, 86, 7, 8

Measurement of Fluid FlowMeasurement of Fluid Flow 99

Measurement of LevelMeasurement of Level 1010

Measurement of Stress-StrainMeasurement of Stress-Strain 1111

Measurement of Time ConstantMeasurement of Time Constant 1212


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RTD & ThermistorRTD & Thermistor

Topic 8: Measurement of Topic 8: Measurement of TemperatureTemperature

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To measure temperature using a RTD & To measure temperature using a RTD & Thermistor.Thermistor.

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Course ObjectivesCourse Objectives


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ThermistorThermistor

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Types of Thermistors


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A A THERMTHERMally sensitive resally sensitive resISTORISTOR (THERMISTOR).-(THERMISTOR).-

Thermistor is a solid semiconducting Thermistor is a solid semiconducting material. Unlike metals, material. Unlike metals, thermistors thermistors respond inversely to temperaturerespond inversely to temperature. i.e., . i.e., their resistance decreases as the their resistance decreases as the temperature increasestemperature increases. The thermistors . The thermistors are usually composed of oxides of are usually composed of oxides of manganese, nickel, cobalt, copper and manganese, nickel, cobalt, copper and several other nonmetals.several other nonmetals.

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Precision Thermistor - 44000 SeriesPrecision Thermistor - 44000 Series

Epoxy EncapsulatedEpoxy Encapsulated Available with 0.1°C and 0.2°C InterchangeabilityAvailable with 0.1°C and 0.2°C Interchangeability High StabilityHigh Stability

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Thermistors Thermistors

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Thermistors Thermistors

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The resistance is generally an exponential The resistance is generally an exponential function of the temperature. The general function of the temperature. The general equation is:equation is:

Where:Where: RRoo= is the resistance at a reference temperature = is the resistance at a reference temperature

TToo

ββ= is a constant characteristic of the material.= is a constant characteristic of the material. TToo= the reference temperature, is generally taken = the reference temperature, is generally taken

as 298K (25ºC).as 298K (25ºC).

1010

oo

th

T

1

T

1

R

Rln

oo

th

T

1

T

1

R

Rln

oo

th

T

1

T

1exp

R

R

oo

th

T

1

T

1exp

R

R


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β β depende del material, temperatura y depende del material, temperatura y construcción. construcción. Β Β ddebe ser determinado ebe ser determinado para cada sensor y debe ser dado por el para cada sensor y debe ser dado por el fabricante.fabricante.

Los termistores son empleados cuando se Los termistores son empleados cuando se requiere alta sensibilidad, respuesta requiere alta sensibilidad, respuesta rápida o alto desempeño, con protección rápida o alto desempeño, con protección pueden ser usados en medios corrosivos, pueden ser usados en medios corrosivos, abrasivos y ácidosabrasivos y ácidos

1111


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Thermistor CurveThermistor Curve

1212


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Theory Theory Experiment Experiment

1313

Circuit for the laboratoryCircuit for the laboratoryWhere:Where:

EEinin= Input Voltage= Input Voltage

RRww= Resistance= Resistance

RRTHTH= Resistance Thermistor= Resistance Thermistor

EEoutout= Output Voltage= Output Voltage

DMM

Ein

-

+

P

Rw

A

RTH

I1

Rw

I2

I4

Rw

B

Eout

C

I3


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AnalysisAnalysis

Potential divider (voltage divider):Potential divider (voltage divider):

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AnalysisAnalysis

The Wheatstone BridgeThe Wheatstone Bridge

1515

DMM

Ein

-

+

P

Rw

A

RTH

I1

Rw

I2

I4

Rw

B

Eout

C

I3


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AnalysisAnalysis

Kirchhoff’s first ruleKirchhoff’s first rule Point A Point CPoint A Point C

1616

I3

I1

Iout

0III 3out1

I2

I4

Iout

0III 4out2


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AnalysisAnalysis

Kirchhoff’s second ruleKirchhoff’s second rule Loop APC Loop ABCLoop APC Loop ABC

Bridge Balanced Bridge Balanced

1717

0RIRIRI w2outoutw1 0RIRIRI TH3outoutw4

0Iout

w2w1 RIRI TH3w4 RIRI

31 II 42 II


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AnalysisAnalysis

Using Potential DividerUsing Potential Divider Loop ABCLoop ABC

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wTH

TH

in

out

wTH

THinout

wTH

THin

ww

winout

TH3w4out

RR

R

2

1

E

E

RR

R

2

1EE

RR

RE

RR

REE

RIRIE


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AnalysisAnalysis

1919

outin

outin

outin

outinin

outin

inw

outin

inwwTH

in

outin

in

out

wTH

TH

wTH

TH

in

out

E2E

E2E

E2E

E2EE21

E2E

E2

R

R

E2E

E2

R

R1

R

RR

1()^

E2

E2E

E

E

2

1

RR

R

RR

R

2

1

E

E

TH

THTH

outin

outinwTH E2E

E2ERR


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Laboratory: Find the value of Laboratory: Find the value of ββ

2020

Table of DataTable of Data

Setup the circuit with a ESetup the circuit with a Einin=10V=10V

Measure the Measure the RRoo at T=25ºC at T=25ºC

Obtain the value of RObtain the value of Rww

Increase temperature and measure Increase temperature and measure EEoutout

In order to find In order to find β, β, use the following equationuse the following equation

Obtain the value of Obtain the value of β β using least squared methodusing least squared method Compare Compare β β with values of literature.with values of literature.

T(ºC)T(ºC) EEoutout(V)(V) ()

outin

outinwTH E2E

E2ERR

o

TH

R

Rln

oo

TH

TTR

R 11ln

mecn 4600 inter - bayamon lecture 9 mechanical measurement and instrumentation mecn 4600 professor:...

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