Temperature Measurement and SI Units

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Questions and Answers

What is a primary advantage of thermocouples?

Cost-effectiveness (correct)

Ability to measure absolute temperatures

Low sensitivity to external factors

High accuracy in all temperature ranges

What is a significant drawback of thermocouples?

They can operate at very high temperatures.

They can only measure temperature differences. (correct)

They require a power supply.

They provide real-time digital output.

Which factor can affect the accuracy of thermocouples?

Thermal expansion of materials

Calibration of reference temperature (correct)

Frequency of the measurement

Type of thermocouple wire used

In what types of systems are thermocouples commonly used?

Temperature control systems Signup and view all the answers

Which of the following is a type of sensor mentioned that is not a thermocouple?

Optical sensor Signup and view all the answers

What value is fixed to define the standard unit of mass, the kilogram?

6.62606 x 10^-34 m^2.kg/s Signup and view all the answers

What constant is used to redefine the mole in the International System of Units?

Avogadro's constant Signup and view all the answers

How is the unit 'second' defined in the most recent SI units update?

Based on the hyperfine transition frequency of cesium 133 Signup and view all the answers

What is the fixed numerical value of the Boltzmann constant used to define the kelvin?

1.3806 x 10^-23 J/K Signup and view all the answers

Which of the following quantities is not a base unit in the International System of Units?

Resistance Signup and view all the answers

Which quantity is defined by the fixed numerical value of the luminous efficacy in the SI units?

Candela Signup and view all the answers

Which type of sensor can be classified as resistive and sensitive to temperature changes?

Thermistor Signup and view all the answers

In the SI unit redefinition, what value is fixed to determine the speed of light?

299,792,458 m/s Signup and view all the answers

What is the behavior of NTC (negative temperature coefficient) materials with regard to resistance and temperature?

Resistance decreases as temperature increases. Signup and view all the answers

How do PTC (positive temperature coefficient) materials react to changes in temperature?

They show increased resistance with increasing temperature. Signup and view all the answers

What is the primary operating principle of a Linear Variable Differential Transformer (LVDT)?

It detects changes in inductance caused by core displacement. Signup and view all the answers

Which property of a Force Sensitive Resistor (FSR) is responsible for its measurement capabilities?

Resistance changes due to dimensional alterations upon applying pressure. Signup and view all the answers

What is the effect of light intensity on the resistance of a light dependent resistor (LDR)?

Resistance decreases with increasing light intensity. Signup and view all the answers

What is the key characteristic of eddy current sensors?

They utilize a fixed core with alternating current to create a fluctuating magnetic field. Signup and view all the answers

Which type of sensor utilizes the piezoresistive effect as a fundamental principle?

Force Sensitive Resistors (FSR) Signup and view all the answers

Which wavelength of light does an LDR exhibit maximum sensitivity towards?

Red light around 680nm Signup and view all the answers

Study Notes

Thermocouples

Used for temperature control systems, industrial furnaces, and research laboratories
Cost-effective and offer a wide temperature measurement range
Limited by their inability to measure absolute temperature; they require a reference temperature and are sensitive to external factors

Units

The International System of Units (SI) establishes base units for fundamental quantities
Base SI units: length (meter), mass (kilogram), time (second), electric current (ampere), temperature (kelvin), luminous intensity (candela), amount of substance (mole)
The definition of the kilogram is based on Planck's constant
The definition of the ampere is based on the elementary charge
The definition of the kelvin is based on the Boltzmann constant
The definition of the mole is based on Avogadro's constant
The second is defined based on the hyperfine transition frequency of Cesium-133
The meter is defined based on the speed of light
The candela is defined based on the luminous efficacy of monochromatic radiation

Types of Sensors

Resistive Sensors

Thermistors (NTC & PTC): Resistance varies with temperature; NTC exhibits decreasing resistance with increasing temperature due to increased free electrons, while PTC exhibits increasing resistance with increasing temperature due to increased molecular vibration.
Light Dependent Resistors (LDR): Resistance varies based on light intensity.
- High resistance in darkness, low resistance when illuminated.
- Cadmium sulfide is an example of LDR material.
Force or Pressure Sensors (FSR): Resistance changes with applied force or pressure.
- Based on the piezoresistive effect (resistivity changes due to pressure).
- Strain gauges use the piezoresistive effect, commonly in bridge circuits.
Displacement Sensors: Measure small distances using potentiometers.

Inductive Sensors

Inductance Changes: Detecting metals by inductance variation with magnetic fields.
Based on Inductance/Mutual Inductance Changes:
- Displacement: Changing inductance by moving the core within an inductor.
- Linear Variable Differential Transformer (LVDT): Measures position, displacement, force, or acceleration by changing inductance of multiple coils around a core.
- Eddy Current Sensors: Use a coil with a fixed core and alternating current to generate a magnetic field.

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Description

Explore the principles of thermocouples used in temperature control systems and their characteristics. Additionally, review the International System of Units (SI) and the base units defining fundamental quantities. This quiz covers essential concepts vital for understanding temperature measurement and unit definitions in science.