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Reliability and Safety Analysis

Reliability and Safety Analysis. Team 4: Shicheng Guo , Kyle Haver , Ethan Price, Wesley Tso. Overview. Device that automatically roasts coffee beans based on a roast level selected by user via GUI. Device uses base popcorn popper, as well as a variety of sensors, to achieve automation.

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Reliability and Safety Analysis

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  1. Reliability and Safety Analysis Team 4: ShichengGuo, Kyle Haver, Ethan Price, Wesley Tso

  2. Overview • Device that automatically roasts coffee beans based on a roast level selected by user via GUI. • Device uses base popcorn popper, as well as a variety of sensors, to achieve automation. • Safety is a major concern due to high power usage and heat generated by device being the main possible causes of critical failures.

  3. PSSCs • An ability to achieve different levels of roasting based on user input. • An ability to detect the temperature of the beans. • An ability to monitor the color of the beans • An ability to interact with the user via GUI • An ability to shut off the device if unusual conditions (dangerously high temperatures, unusual color in roasting area, or timeout) are detected.

  4. Components Chosen • Components listed in order of “closeness” to power and heat of device. • AC Relay (ST24D12): controls heating coil. • DC Relay (LCA717S): controls cooling fans and rotates beans. • Microprocessor (ATMEGA8A-AU): controls overall operation, including the relays and safety checks. • Voltage Regulator (LM7805CT): regulates power to microprocessor, therefore indirectly affecting relays. • Transformer (273-1512): supplies power to microprocessor circuit, including voltage regulator, relays, voltage regulator, and microprocessor.

  5. AC Relay • λp = λb * πQ * πE Failures/10^6 hours. • λp = 1.6 Failures/10^6 hours.

  6. DC Relay • λp = λb * πQ * πE Failures/10^6 hours. • λp = 1.6 Failures/10^6 hours.

  7. Microprocessor • λp = (C1 * π T + C2 * π E) * xQ * xL Failures/10^6 hours. • λp = 0.2818 Failures/10^6 hours.

  8. Voltage Regulator • λp = λb * πT * πS * πC * πQ * πEFailures/10^6 hours. • λp = 0.02448 Failures/10^6 hours.

  9. Transformer • λp = λb * πQ * πE Failures/10^6 hours. • λp = 0.057 Failures/10^6 hours.

  10. Other Components • Sensors (Microphone, Camera, Thermometer) • Rotary Encoder • LED • Display

  11. Summary • Most prone to critical failures are the relays. • Possible design alternatives: • Have two relays ORed together for each current relay. For AC Relay, OR for off functionality. For DC relay, OR for on functionality. • Spend way more money on higher grade relays. • Neither are very appealing.

  12. Links • AC Relay Data Sheet: http://www.teledynerelays.com/pdf/industrial/st.pdf • DC Relay Data Sheet: http://www.clare.com/home/pdfs.nsf/www/LCA717.pdf/$file/LCA717.pdf • Microprocessor Web Link: http://www.atmel.com/devices/atmega168a.aspx • Voltage Regulator Data Sheet: http://www.fairchildsemi.com/ds/LM/LM7805.pdf • Transformer Web Link: http://www.radioshack.com/product/index.jsp?productId=2102703

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