MECN 4600 Inter - Bayamon Lecture 9 Mechanical Measurement and Instrumentation MECN 4600 Professor: Dr. Omar E. Meza Castillo Department of Mechanical Engineering Inter American University of Puerto Rico Bayamon Campus

Lecture 9 MECN 4600 Inter - Bayamon 2 Tentative Lecture Schedule TopicLecture Basic Principles of Measurements Response of Measuring Systems, System Dynamics Error & Uncertainty Analysis 1, 2 and 3 Sensor & Transducers Basic Electronics, Signal Processing 4 Measurement of Pressure 5 Measurement of Temperature 6, 7, 8 Measurement of Fluid Flow 9 Measurement of Level 10 Measurement of Stress-Strain 11 Measurement of Time Constant 12

Lecture 9 MECN 4600 Inter - Bayamon RTD & Thermistor Topic 8: Measurement of Temperature 3

Lecture 9 MECN 4600 Inter - Bayamon  To measure temperature using a RTD & Thermistor. 4 Course Objectives

Lecture 9 MECN 4600 Inter - Bayamon Thermistor 5 Types of Thermistors

Lecture 9 MECN 4600 Inter - Bayamon Thermistor  A THERMally sensitive resISTOR (THERMISTOR).-  Thermistor is a solid semiconducting material. Unlike metals, thermistors respond inversely to temperature. i.e., their resistance decreases as the temperature increases. The thermistors are usually composed of oxides of manganese, nickel, cobalt, copper and several other nonmetals. 6

Lecture 9 MECN 4600 Inter - Bayamon Precision Thermistor Series  Epoxy Encapsulated  Available with 0.1°C and 0.2°C Interchangeability  High Stability 7

Lecture 9 MECN 4600 Inter - Bayamon Thermistors 8

Lecture 9 MECN 4600 Inter - Bayamon Thermistors 9

Lecture 9 MECN 4600 Inter - Bayamon Thermistor  The resistance is generally an exponential function of the temperature. The general equation is: Where:  R o = is the resistance at a reference temperature T o  β= is a constant characteristic of the material.  T o = the reference temperature, is generally taken as 298K (25ºC). 10

Lecture 9 MECN 4600 Inter - Bayamon Thermistor  β depende del material, temperatura y construcción. Β debe ser determinado para cada sensor y debe ser dado por el fabricante.  Los termistores son empleados cuando se requiere alta sensibilidad, respuesta rápida o alto desempeño, con protección pueden ser usados en medios corrosivos, abrasivos y ácidos 11

Lecture 9 MECN 4600 Inter - Bayamon Thermistor Curve 12

Lecture 9 MECN 4600 Inter - Bayamon Theory  Experiment 13  Circuit for the laboratory Where:  E in = Input Voltage  R w = Resistance  R TH = Resistance Thermistor  E out = Output Voltage DMM E in - + P RwRw A RT H I1I1 RwRw I2I2 I4I4 RwRw B E out C I3I3

Lecture 9 MECN 4600 Inter - Bayamon Analysis Potential divider (voltage divider): Potential divider (voltage divider): 14

Lecture 9 MECN 4600 Inter - Bayamon Analysis The Wheatstone Bridge The Wheatstone Bridge 15 DMM E in - + P RwRw A R TH I1I1 RwRw I2I2 I4I4 RwRw B E out C I3I3

Lecture 9 MECN 4600 Inter - Bayamon Analysis Kirchhoff’s first rule Kirchhoff’s first rule Point A Point C Point A Point C 16 I3I3 I1I1 I out I2I2 I4I4

Lecture 9 MECN 4600 Inter - Bayamon Analysis Kirchhoff’s second rule Kirchhoff’s second rule Loop APC Loop ABC Loop APC Loop ABC Bridge Balanced Bridge Balanced 17

Lecture 9 MECN 4600 Inter - Bayamon Analysis Using Potential Divider Using Potential Divider Loop ABC Loop ABC 18

Lecture 9 MECN 4600 Inter - Bayamon Analysis 19

Lecture 9 MECN 4600 Inter - Bayamon Laboratory: Find the value of β 20  Table of Data  Setup the circuit with a E in =10V  Measure the R o at T=25ºC  Obtain the value of R w  Increase temperature and measure E out  In order to find β, use the following equation  Obtain the value of β using least squared method  Compare β with values of literature. T(ºC)E out (V)E out (V) () ()