Thermocouple Temperature Measurement
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Questions and Answers

What is the characteristic of the resistance of a thermistor with respect to temperature?

  • Resistance changes linearly with temperature
  • Resistance decreases exponentially with temperature (correct)
  • Resistance remains constant with temperature
  • Resistance increases exponentially with temperature

    • What type of thermocouple configuration is shown in the figure?

  • Thermocouple with single reference junction
  • RTD thermocouple configuration
  • Standard thermocouple configuration
  • Thermocouple with dual reference junctions (correct)

    • What is the characteristic of the resistance of an RTD?

  • Resistance changes exponentially with temperature
  • Resistance remains constant with temperature
  • Resistance decreases with temperature
  • Resistance increases with temperature (correct)

    • What is the purpose of the internal reference junctions in a thermocouple?

    <p>To provide temperature compensation</p> Signup and view all the answers

    What type of devices are RTDs and thermistors?

    <p>Thermoresistive sensors</p> Signup and view all the answers

    What is the relationship between temperature and resistance in an RTD?

    <p>Resistance increases with temperature</p> Signup and view all the answers

    What is the characteristic of the TCR (Temperature Coefficient of Resistance) in an RTD?

    <p>It is not a constant in some cases</p> Signup and view all the answers

    What is the purpose of the equations used in RTD measurements?

    <p>To establish the relationship between temperature and resistance</p> Signup and view all the answers

    What is the characteristic of PTC thermistors compared to NTC thermistors?

    <p>More sensitive than NTC thermistors</p> Signup and view all the answers

    What is the common application of thermistors?

    <p>In digital thermometers</p> Signup and view all the answers

    What is the advantage of thermistors over RTDs?

    <p>Better accuracy</p> Signup and view all the answers

    What type of thermistors are available depending on the type of material?

    <p>PTC thermistors</p> Signup and view all the answers

    What type of thermistors are commonly used in automobiles?

    <p>NTC thermistors</p> Signup and view all the answers

    What is the main characteristic of thermistors that makes them suitable for temperature measurement?

    <p>High sensitivity to temperature</p> Signup and view all the answers

    What type of thermistors are deposited on ceramic substrate?

    <p>Deposited thermistors</p> Signup and view all the answers

    What is the primary application of thermistors?

    <p>Temperature measurement</p> Signup and view all the answers

    What is the most common principle used in temperature measurement?

    <p>Contraction or expansion of solid, liquid or gas</p> Signup and view all the answers

    What is the net source of emf between pair of points in any individual electrically conducting material due to a difference of temperature between them?

    <p>Seebeck effect</p> Signup and view all the answers

    What is the formula to calculate the emf between 2 points in a thermocouple?

    <p>∆E = σT</p> Signup and view all the answers

    What is the purpose of a thermocouple?

    <p>To produce a voltage which is proportional to the temperature of the junction</p> Signup and view all the answers

    Which of the following is NOT a type of temperature sensor?

    <p>Bourdon tube</p> Signup and view all the answers

    What is the principle of operation of an orifice type flow meter?

    <p>Change in pressure due to restriction</p> Signup and view all the answers

    Which of the following temperature sensors works on the principle of change in electric resistance of a material?

    <p>RTD (Resistive temperature devices)</p> Signup and view all the answers

    What is the purpose of a thermoelectric junction in a thermocouple?

    <p>To produce a voltage which is proportional to the temperature of the junction</p> Signup and view all the answers

    Study Notes

    Temperature Measurement

    • Thermocouples consist of two dissimilar metals (A, B) and extension leads (C, D) with internal reference junctions (A', B') for temperature compensation.
    • Thermocouples can be configured with dual reference junctions.

    Thermoresistive Sensors

    • Resistance of the sensing element changes with temperature.
    • There are two basic types of thermoresistive sensors: RTDs (Resistance Temperature Devices) and Thermistors.

    Resistance Temperature Devices (RTD)

    • The resistance of the device usually increases with temperature (PTCs).
    • RTDs are constructed of metallic wire wound around a ceramic or glass core.
    • In some cases, the TCR (Temperature Coefficient of Resistance) is not a constant, and relations have been established based on actual measurements.
    • Coefficients are specified by standards measurements.

    Thermistors

    • Thermistors are semiconductor metal oxide devices where resistance changes exponentially with temperature.
    • Usually, resistance decreases with increasing temperature (NTC thermistors).
    • There are different types of thermistors, including bead thermistors, chip thermistors, and deposited thermistors on ceramic substrate.
    • PTC thermistors are also available, depending on the type of material.
    • Thermistors are more sensitive than RTDs, but have a lower operating range.

    Position, Displacement, and Speed Measurement

    Linear Potentiometer

    • Linear potentiometers are used for rectilinear motion measurements, while rotary potentiometers are used for angular motion measurements.
    • Linear potentiometers are electromechanical devices containing a fixed resistive element and a conductive wiper that slides against the element.
    • The output is given by vo = kx, where x is the displacement, but the actual relationship is non-linear due to finite loading impedance at output terminals.

    Proximity Sensor

    • Proximity sensors generally consist of an element that changes its state when an object is close by, but not actually touching it.

    Pressure Sensors

    • Most common pressure sensing element types include Bourdon tube, diaphragm, capsule, and bellows types.

    Flow Measurement

    • Different types of techniques used to estimate the flow rate of fluids include Coriolis meters, electromagnetic principle, ultrasonic flow meters, vortex flow meters, and orifice/nozzle/venturi type flow meters.
    • Traditional method is to measure using an orifice plate, which causes a change in pressure.

    Temperature Measurement

    • Most commonly based on contraction or expansion of solid, liquid, or gas, and change in the electric resistance of a material.
    • Common sensors and techniques include thermocouples, RTD (Resistive temperature devices), pyroelectric devices, thermal imaging, and bimetallic thermometers.

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    Related Documents

    IS 1281 Engineering Measurements Lecture 10 PDF

    Description

    Learn about thermocouples, thermocouple circuits, and standard thermocouple configurations in temperature measurement.

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