Intrumentation and Control Engineering Handouts
THERMAL DETECTORS
INSTRUMENTATION AND CONTROL ENGINEERING MODULE 1
INTRODUCTION
• Temperature
– Is a measure of the kinetic energy of the material in question
• Kinetic energy is a measure of the activity of the atoms of any material
– The measure of the speed of an atom or molecules which they move. – expressed in terms of any of several arbitrary scales, such as Fahrenheit, Celsius, or Kelvin
Measuring Device
• Thermal Detectors
– An instrument or device which quantifies temperature
• Types
– Thermometer – Resistance temperature detector (RTD) – Thermocouples
RTD
• The resistance of certain metals will change as temperature changes. This characteristic is the basis for the operation of an RTD. • a temperature sensor which measures temperature using the principle that the resistance of a metal changes with temperature.
Theory Behind RTD
• Classification of materials:
– Conductors – tends to increase their resistivity with an increase in temperature – Insulators – tends to decrease resistivity with an increase in temperature
• Free electrons - migrates
– Conductors – many free electrons – Insulators – hardly any free electrons
• The effect of heat – makes atom vibrates
– Conductors
• Causes collisions between the free electrons and the captive electrons • Collision uses up some energy from the free electrons, thus cause increasing in resistance • Therefore, at high temperature, resistance is greater
– Insulators
• If heated sufficiently, the atoms vibrates violently enough to shake some of their captive electrons free, creating free electrons • Therefore, at high temperature, resistance is lower
As temperature increases, resistance increases and, conversely, as temperature decreases, resistance decreases
RTD Construction
• RTDs act like an electric transducer, converting changes in temperature to voltage signals by the measurement of resistance. • The metals that are best suited for use as RTD sensors are pure,
INSTRUMENTATION AND CONTROL ENGINEERING MODULE 1
INTRODUCTION
• Temperature
– Is a measure of the kinetic energy of the material in question
• Kinetic energy is a measure of the activity of the atoms of any material
– The measure of the speed of an atom or molecules which they move. – expressed in terms of any of several arbitrary scales, such as Fahrenheit, Celsius, or Kelvin
Measuring Device
• Thermal Detectors
– An instrument or device which quantifies temperature
• Types
– Thermometer – Resistance temperature detector (RTD) – Thermocouples
RTD
• The resistance of certain metals will change as temperature changes. This characteristic is the basis for the operation of an RTD. • a temperature sensor which measures temperature using the principle that the resistance of a metal changes with temperature.
Theory Behind RTD
• Classification of materials:
– Conductors – tends to increase their resistivity with an increase in temperature – Insulators – tends to decrease resistivity with an increase in temperature
• Free electrons - migrates
– Conductors – many free electrons – Insulators – hardly any free electrons
• The effect of heat – makes atom vibrates
– Conductors
• Causes collisions between the free electrons and the captive electrons • Collision uses up some energy from the free electrons, thus cause increasing in resistance • Therefore, at high temperature, resistance is greater
– Insulators
• If heated sufficiently, the atoms vibrates violently enough to shake some of their captive electrons free, creating free electrons • Therefore, at high temperature, resistance is lower
As temperature increases, resistance increases and, conversely, as temperature decreases, resistance decreases
RTD Construction
• RTDs act like an electric transducer, converting changes in temperature to voltage signals by the measurement of resistance. • The metals that are best suited for use as RTD sensors are pure,