Optoelectronic and Miscellaneous Devices (Unit 9) - PDF
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Uploaded by FabulousMoldavite6621
Lambton College of Applied Arts and Technology
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This document provides an overview of optoelectronic and miscellaneous devices, including topics such as LEDs, semiconductor lasers, detectors, waveguides, and optical disks. It also covers thermistors, thermocouples and RTDs, which are temperature sensing devices.
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Unit 9 Optoelectronic and Miscellaneous Devices - 4 Active Optical Devices LEDS Semiconductor lasers Detectors Passive Optical Devices Waveguides Optical Disk Passive Optical Devices Waveguides Waveguides for DVD Players Plastic Optical Fiber Optical cables are used for digital audio...
Unit 9 Optoelectronic and Miscellaneous Devices - 4 Active Optical Devices LEDS Semiconductor lasers Detectors Passive Optical Devices Waveguides Optical Disk Passive Optical Devices Waveguides Waveguides for DVD Players Plastic Optical Fiber Optical cables are used for digital audio connections PMMA (polymethyl methacrylate) core Features: - Application light wavelength 655 + or - 30 nm - Attenuation less than or equal to 0.25 dB per meter - Bend Radius greater than or equal to 17 mm - Connection loss less than or equal to 0.5 dB 350 Unit 9 F2013 IC 1 Thermistors Thermistors – a temperature-sensitive resistor (are resistors whose value changes with temperature = temperature-to-voltage conversion). It is not a junction device and is constructed of germanium, silicon, or a mixture of oxides of cobalt strontium or manganese. The compound employed determines whether the device has a positive or a negative temperature coefficient. Thermistors are negative coefficient devices - their resistance decreases as the temperature increases. Note: in particular that at room temperature (200C) the resistance of the thermistor is aprox. 5000 Ω and at 1000C the resistance decreased to 100 Ω A temperature span of 800C therefore results in a 50:1 change in resistance. The change in resistance is typically 3% to 5% per degree change in temperature. Example: 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. 350 Unit 9 F2013 IC 2 THERMOCOUPLE In 1821, Thomas Seebeck discovered if metals of two different materials were joined at both ends and one end was at a different temperature than the other, a current was created. This phenomenon is known as the Seebeck effect and is the basis for all thermocouples (a conductor generates a voltage when subjected to a temperature gradient.). A thermocouple is a type of temperature sensor, which is made by joining two dissimilar metals at one end. The joined end is referred to as the Hot Junction. The other end of these dissimilar metals is referred to as the Cold End or Cold Junction. The cold junction is actually formed at the last point of thermocouple material Certain combinations of metals must be used to make up the thermocouple pairs. - If there is a difference in temperature between the hot junction and cold junction, a small voltage is created. This voltage is referred to as an EMF and can be measured and in turn used to indicate temperature. - The voltage created by a thermocouple is extremely small and is measured in terms of millivolts. (the human body creates a larger millivolt signal than a thermocouple) - To establish a means to measure temperature with thermocouples, a standard scale of millivolt outputs was established. This scale was established using 320F (0°C) as the standard cold junction temperature (320F (0°C) = 0 mV output). 350 Unit 9 F2013 IC 3 Base metal thermocouples (T/C): Base metal thermocouples are known as Types E, J, K, T and N (≈1000°C) and comprise the most commonly used category of thermocouple. The conductor materials in base metal thermocouples are made of common and inexpensive metals such as Nickel, Copper and Iron. Noble metal types: (≈1700°C) Platinum, Rhodium. Metal-sheathed thermocouple (partially sectioned). Thermocouple terminations: Enclosed head (Open head and Plug and Jack are also available) Resistance Temperature Detectors - RTD Many manufacturing plants require accurate monitoring and control of process temperature. Resistance temperature detectors are sensors with resistance values that are proportional to temperature. They can withstand temperatures from – 2000 C (- 328 F) to those approaching 10000 C (1,800 F). Typically manufactured from platinum, RTDs are highly stable and tolerate aggressive conditions, making them suitable for most industrial environments. RTDs are characterized by a linear positive change in resistance with respect to temperature. 350 Unit 9 F2013 IC 4 They exhibit the most linear signal with respect to temperature of any electronic sensing device. Adopted worldwide, the European standard for RTDs specifies a nominal 100 Ω resistance and a uniform temperature coefficient of resistance between zero and 100 C. There are some other typical base resistance values available for platinum thin-film RTDs includes 100Ω, 500Ω and 1000Ω. For other element types, typical base values include 120Ω for nickel (1000Ω or 1500Ω for Balco= nickel-iron alloy) 350 Unit 9 F2013 IC 5