mecn 4600 inter - bayamon lecture 8 mechanical measurement and instrumentation mecn 4600 professor:...
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LectureLecture
88Mechanical 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
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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
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Measurement of PressureMeasurement of Pressure 55
Measurement of TemperatureMeasurement of Temperature 66
Measurement of Fluid FlowMeasurement of Fluid Flow 77
Measurement of LevelMeasurement of Level 88
Measurement of Stress-StrainMeasurement of Stress-Strain 99
Measurement of Time ConstantMeasurement of Time Constant 1010
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RTD & ThermistorRTD & Thermistor
Topic 7: Measurement of Topic 7: 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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RTDRTD
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Types of RTD
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RTDRTD
RESISTANCE TEMPERATURE DETECTORSRESISTANCE TEMPERATURE DETECTORS (RTDs).- (RTDs).- RTD’s functions as a result of RTD’s functions as a result of increasing increasing
resistance resistance in proportion to in proportion to increasing increasing temperaturetemperature. i.e, with a known current, as . i.e, with a known current, as temperature increases, voltage increases. As a temperature increases, voltage increases. As a known current is placed through the RTD, the known current is placed through the RTD, the output voltage indicates RTD resistance. Since the output voltage indicates RTD resistance. Since the relationship between the resistance and relationship between the resistance and temperature is known, the temperature can thus temperature is known, the temperature can thus be determined.be determined.
The resistivity of the metal used in a RTD is The resistivity of the metal used in a RTD is dependent upon the temperature. dependent upon the temperature. PlatinumPlatinum has has the best range and is the most common metal the best range and is the most common metal used.used.
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Lecture 8Lecture 8MEC
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Suitable for Low or very High TemperaturesSuitable for Low or very High Temperatures Tolerant of Thermal ShocksTolerant of Thermal Shocks Good Vibration ResistanceGood Vibration Resistance Alpha = 0.00385Alpha = 0.00385
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Temperature Range -200 to 600°CTemperature Range -200 to 600°C Alpha = .00385 Standard Alpha = .00385 Standard RRoo = 100 = 100Ω @ 0°Ω @ 0°CC
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RTDRTD
The general equation is:The general equation is:
La ecuación general puede ser simplificada para La ecuación general puede ser simplificada para materiales comunes como platino, cobre, etc con materiales comunes como platino, cobre, etc con bajos porcentajes de error en las mediciones.bajos porcentajes de error en las mediciones.
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oo
TT1R
R
...TTTT1R)T(RR ooo
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RTDRTD
Where:Where: R= Resistance at temperature TR= Resistance at temperature T RRoo= Resistance at temperature T= Resistance at temperature Too
TToo= Temperature of reference= Temperature of reference T= TemperatureT= Temperature αα= Resistivity Coefficient= Resistivity Coefficient
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Theory Theory Experiment Experiment
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Circuit for the laboratoryCircuit for the laboratory
Where:Where: eeoo= Voltage through RTD= Voltage through RTD
RRbb= Resistance= Resistance
RRRTDRTD= Resistance RTD= Resistance RTD
eeii= Voltage of fem= Voltage of fem
D
M
M
ei
(fem)
+I
Rb
RRTD eo
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AnalysisAnalysis
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Kirchoff’s Law:Kirchoff’s Law:
Law of OhmLaw of Ohm
0RRIe
0IRIRe
RTDbi
RTDbi
RTDbRTD
oi
RTD
oRTDo
RRR
ee
R
eIIRe
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AnalysisAnalysis
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Combining previous Equations:Combining previous Equations:
RTDiRTDobo
RTDb
RTD
i
o
ReReRe
RR
R
e
e
boi
oRTD R
ee
eR
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Laboratory: Find the value of Laboratory: Find the value of αα
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Table of DataTable of Data
Setup the circuit with a eSetup the circuit with a eii=10V=10V
Measure the Measure the RRoo at T=0ºC at T=0ºC
Obtain the value of RObtain the value of Rbb
Increase temperature and measure Increase temperature and measure eeoo
In order to find In order to find α, α, use the following equationuse the following equation
Obtain the value of Obtain the value of α α using least squared methodusing least squared method Compare Compare α α with values of literature.with values of literature.
T(ºC)T(ºC) eeoo(V)(V) ()boi
oRTD R
ee
eR
o
RTD
R
R
oo
RTD TT1R
R