Optoelectronic Devices and Thermistors Quiz

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Questions and Answers

What type of optical fiber is used in waveguides for DVD players?

Metallic Optical Fiber

Plastic Optical Fiber (correct)

Ceramic Optical Fiber

Glass Optical Fiber

What characteristic of a thermistor is true as temperature increases?

Resistance increases rapidly

Resistance remains constant

Resistance decreases (correct)

Resistance doubles

What is the primary function of a thermocouple?

To control fuel flow

To convert temperature differences into voltage (correct)

To amplify signal strength

To measure pressure variations

At room temperature (20°C), what is the approximate resistance of the thermistor?

5000 Ω Signup and view all the answers

What does PMMA stand for in the context of optical cable cores?

Polymethyl methacrylate Signup and view all the answers

What is the expected attenuation rate for the optical cable mentioned?

0.25 dB per meter Signup and view all the answers

What happens to the output voltage of a thermistor-based circuit when temperature increases?

It increases Signup and view all the answers

What is the significance of the bend radius being greater than or equal to 17 mm in optical fibers?

Prevents fiber fracture Signup and view all the answers

What is the output voltage of a thermocouple at the standard cold junction temperature of 0°C?

0 mV Signup and view all the answers

Which of the following thermocouple types is classified as a base metal thermocouple?

Type J Signup and view all the answers

Resistance Temperature Detectors (RTDs) are known for which characteristic in relation to temperature?

Linear positive change in resistance Signup and view all the answers

Which of the following base resistance values is standard for platinum RTDs?

100 Ω Signup and view all the answers

What temperature range can Resistance Temperature Detectors (RTDs) typically withstand?

-200°C to 10000°C Signup and view all the answers

Which material is commonly used to manufacture RTDs for their stability?

Platinum Signup and view all the answers

What is an example of a noble metal thermocouple type?

Type R Signup and view all the answers

What characteristic does a metal-sheathed thermocouple offer?

Improved durability in harsh environments Signup and view all the answers

Study Notes

Optoelectronic and Miscellaneous Devices

Active Optical Devices: Include LEDs, Semiconductor lasers, and Detectors.

Passive Optical Devices

Waveguides: Used in DVD players, and for digital audio connections. Optical cables use waveguides for digital audio.
Optical Disk: A type of passive optical device.

Plastic Optical Fiber

Structure: This includes a core, cladding, and buffer.
Total Internal Reflection: Light rays are reflected within the fiber due to the difference in refractive index.
Material: PMMA (polymethyl methacrylate) is used for the core
Features: Applications wavelengths at 655nm +/- 30nm, attenuation less than or equal to 0.25 dB/meter, bend radius greater than or equal to 17mm, connection loss less than or equal to 0.5 dB.

Thermistors

Definition: Temperature-sensitive resistors whose resistance changes with temperature.
Construction: Made of germanium, silicon, or a mixture of oxides of cobalt, strontium, or manganese.
Temperature Coefficient: Negative temperature coefficient; resistance decreases as temperature increases.
Typical values: at 20°C approx, 5000Ω and at 100°C resistance decreases to 100Ω.
Resistance Change per Degree: Typically 3% to 5% per degree change in temperature.
Applications: Industrial temperature control system. The output voltage of the circuit is proportional to the thermistor resistance. The output voltage goes to an valve interface to control the flow of the fuel to the burner based on voltage.

Thermocouples

Discovery: Invented by Thomas Seebeck in 1821
Seebeck Effect: When two different metals are joined at both ends and one end is at a different temperature than the other, a current is created.
Hot Junction: The joined end where the two dissimilar metals are joined
Cold Junction: The other end of the dissimilar metals
Voltage Generation: When there's a temperature difference between the hot and cold junctions, a voltage is created (EMF).
Measurement: This voltage (EMF) is measured in millivolts (mV). The human body produces a larger millivolt signal than a thermocouple.
Standard Scale: Established using 32°F (0°C) as the standard cold junction temperature (0 mV output).

Base Metal Thermocouples (T/C)

Types: Types E, J, K, T, and N (approx 1000°C)
Materials: Common/inexpensive metals like nickel, copper, and iron

Noble Metal Thermocouples

Types: Platinum, Rhodium (approx 1700°C)

Resistance Temperature Detectors (RTDs)

Purpose: Used for monitoring and controlling process temperature in many manufacturing plants.
Mechanism: Resistance values proportional to temperature.
Temperature Range: Can withstand -200°C to 1000°C.
Material: Typically made from platinum.
Characteristics: Highly stable and tolerate aggressive industrial environments. Linear positive change in resistance with respect to temperature.
Standard: European standard for RTDs specifies a nominal 100 Ω resistance and a uniform temperature coefficient between zero and 100°C.
Other values: 100Ω, 500Ω, 1000Ω, 1202 for nickel are common values.

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Description

Test your knowledge on optoelectronic devices, including active optical devices like LEDs and semiconductor lasers, as well as passive devices like waveguides and optical disks. This quiz also covers the structure and features of plastic optical fibers and thermistors. Dive into the fascinating world of optics and electronics!