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Questions and Answers
What is the primary purpose of thermocouples in aviation?
What is the primary purpose of thermocouples in aviation?
Which metals are used in modern engines for thermocouples?
Which metals are used in modern engines for thermocouples?
What happens when two different metals are placed in an electrically conducting liquid?
What happens when two different metals are placed in an electrically conducting liquid?
What is the unit of measure for the capacity of a lead battery?
What is the unit of measure for the capacity of a lead battery?
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Which type of battery can be recharged and reused?
Which type of battery can be recharged and reused?
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What is the process called when an electric current is passed through a liquid, leading to decomposition?
What is the process called when an electric current is passed through a liquid, leading to decomposition?
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Which of the following gases is commonly used in light bulbs to protect the filament from burning?
Which of the following gases is commonly used in light bulbs to protect the filament from burning?
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Who developed the Electron Beam Tube technology, which is foundational for modern oscilloscopes?
Who developed the Electron Beam Tube technology, which is foundational for modern oscilloscopes?
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In the context of current flow, where do electrons typically move towards when a voltage is applied?
In the context of current flow, where do electrons typically move towards when a voltage is applied?
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What does permittivity describe in relation to electrical fields?
What does permittivity describe in relation to electrical fields?
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Study Notes
Thermoelectric Voltage
- The thermoelectric voltage is dependent on the temperature difference between the junction and the free ends, and the combination of metals.
- Some common metal combinations and their voltage outputs per 100°C:
- Chromel - Alumel: 4.2 mV
- Bismuth - Antimony: 10.0 mV
- Constantan - Copper: 4.2 mV
- Platinum - Platinum-Rhodium: 1.0 mV
Thermocouples
- Thermocouples measure temperature ranging from 200°C to 2300°C.
- In aviation, they are primarily used to measure Exhaust Gas Temperatures (EGT) of engines.
- Chromel and Alumel are frequently used in modern engines.
- The thermocouple part is called the “Hot Junction” and the indicator part is called the “Cold Junction.”
- A balancing resistor is used to compensate for differences in length and resistance.
- Multiple thermocouples can be connected in parallel in a housing referred to as a “Junction Box.”
Photocells
- Photocells convert light into electrical energy.
- Voltage is generated when light hits a photocell.
Galvanic Cells
- Electrochemical reactions can generate electrical voltage.
- Two dissimilar metals immersed in an electrically conducting liquid (e.g., water with sulfuric acid) create a voltage difference.
- Galvanic cells are categorized as Primary Cells (batteries) and Secondary Cells (rechargeable power supplies).
Primary Cells
- Zinc-Carbon is a common battery material combination.
- Primary cells are not rechargeable.
Secondary Cells
- The rated voltage of a lead battery cell is 2 V.
- Lead batteries are discharged when the cell voltage reaches 1.83 V.
- Their capacity is measured in Ampere Hours (Ah) (e.g., 50 Ah is 5 A * 10 Hours).
- Aircraft commonly use Nickel-Cadmium batteries.
Static Electricity
- When a body is charged, the charges repel each other, causing an even distribution across the body's surface.
Coulomb’s Law
- Describes the force between electrical charges.
- Formula:
F = 1 / 4πε) (Q1 * Q2 / d2) -
F= Force -
Q= Charge -
ε= Permittivity -
d= Distance between the Charges -
π= pi (3.14) - Permittivity represents the ability of a medium (e.g., air) to conduct electric fields.
Electrical Conductivity
- Metals have free electrons that allow for electrical conductivity.
- Electrons flow from the negative to the positive poles when a voltage is applied.
Electrolysis
- The process of decomposing a liquid by passing an electric current through it.
- Electrolysis is used in various applications, including galvanizing and battery charging.
- The electrically conducting liquid is called an electrolyte.
- Electrons move at a speed of a few millimeters per second.
Electrical Engineering & Gases
- Gases are used in various electrical engineering applications.
- Nitrogen, Argon, or Krypton are used to prevent filament burnout, oxidation, and vaporization in light bulbs (> 60 W).
- Halogen bulbs also incorporate halogens (e.g., Iodine or Bromine).
Gas Discharge
- The process of electrical conduction through a gas.
Oscillographs/Oscilloscopes
- Visualize rapidly changing electrical processes.
- Electron beam oscilloscopes are widely used for their ease of operation, versatility, and shock resistance.
Electron Beam Tube
- Invented by K.F. Braun, a German physicist.
- Also known as the "Braun" tube.
Electron Gun
- Developed by A.R. Wehnelt, a German physicist.
- Bundled electrons for various applications, including television tubes.
Voltage Units
- 1 V = 1000 mV
- 1 mV = 0.001 V
- 1 kV = 1000 V
Common Voltages
- Radio Aerial - 0.1 uV... 5 mV
- Telephone - 1 mV... 800 mV
- Single Cell Battery - 1.5 V
- Mains Voltage - 230 V... 400 V
- Power Line - 6 kV... 380 kV
- Lightning - Several MV
Hazardous Voltages
- 50 V AC or 120 V DC
Direct Current (DC)
- Current flows constantly in one direction.
- The direction of electron flow depends on the polarity of the applied voltage.
Alternating Current (AC)
- Current periodically changes direction.
Conventional/Technical Current Flow
- Current flows from the positive pole to the negative pole.
Electron Flow
- Current flows from the negative pole to the positive pole.
Frequency
- Measured in Hertz (Hz) or Cycles Per Second (CPS)
- Represents how quickly a voltage changes direction.
Aircraft Electrical Systems
- Standard Voltage: 115 V and 200 V
- Frequency: 400 Hz
Voltage Generation Methods
- Friction
- Pressure
- Heat
- Light
- Chemical Action
- Induction
Friction
- Early Greeks observed the "Triboelectric Effect" when rubbing amber with wool or leather cloth.
- Generating static electricity through friction with insulators causing charge separation.
- Can reach high voltages in the kV range.
Pressure
- Deforming piezo crystals creates voltage.
- This is known as the "Piezoelectric Effect."
Heat
- Thermionic emission: Heat causes electrons to be emitted from a metal, resulting in voltage generation.
- This method is used to measure Exhaust Gas Temperature (EGT) in aircraft turbines.
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Description
This quiz explores the principles and applications of thermoelectric voltage and thermocouples, focusing on their metal combinations and measurement capabilities. It also briefly covers the functionality of photocells in converting light into electrical energy. Test your knowledge on these key concepts in thermoelectric and sensor technology.
