Prof. Katherine Candler! E80 - Spring 2013!!!!! (Notes adapted from Prof. Qimin Yang s lecture, Spring 2011)!

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1 Prof. Katherine Candler E80 - Spring 2013 (Notes adapted from Prof. Qimin Yang s lecture, Spring 2011)

2 } } (just for fun): 1

3 } What sort of data might you want to collect from your rocket? 2

4 } Atmospheric phenomena Temperature Humidity Pressure Trace gas concentration Dust concentration Particle concentration } Rocket performance data Altitude Velocity Acceleration Vibration Rotation rate Internal temperatures 3

5 } Gas Sensor } Humidity Sensor } Pressure Sensor } Vibration Sensor 4

6 } What characteristics are important to consider when selecting a sensor? Input range Output range Supply voltage Sensitivity Operating temperature range Response time Accuracy Size Cost 5

} Solid electrolyte sensors [NO 2, CO 2, O 2 ] }

7 } Solid electrolyte sensors [NO 2, CO 2, O 2 ] } Metal oxide sensors [combustible & toxic gases] } Catalytic bead sensors [combustible gases] } Electrochemical sensors [toxic gases & oxygen] 6

8 } Presence of gas (e.g., CO 2 ) leads to chemical reactions Cathode: 2Li + + CO 2 + ½O 2 + 2e - = Li 2 CO 3 Anode: 2Na + + ½O 2 + 2e - = Na 2 O Overall chemical reaction: Li 2 CO 3 + 2Na + = Na 2 O + 2Li + + CO 2 } Chemical reactions generate an EMF: EMF = E c RT (Nernst Equation) 2F ln(p CO2 ) E c = constant cell potential under standard conditions [V] R = ideal gas constant = 8.31 J/(mol-K) T = absolute temperature [K] F = Faraday constant = 9.65 x 10 4 C/mol P CO2 = partial pressure of CO 2 gas 7

9 } Adsorption of gas increases conductivity of material (e.g., SnO 2 ) solidstate.pdf N. Barsan and U. Weimar, Conduction Model of Metal Oxide Gas Sensors, J. Electroceramics, Dec

10 } Presence of combustible gas increases resistance of sensor material (catalytic bead) 9

11 } Reaction with gas produces a current that is proportional to the gas concentration 10

12 } Partial pressure is a way to express the concentration of a gas: Partial pressure = (total absolute pressure) x (volume fraction of gas component) } For low concentrations, we often use ppm or ppb : 1 ppm means 1 molecule (e.g., of CO 2 ) for 1 million molecules of gas 1 ppb means 1 molecule (e.g., of CO 2 ) for 1 billion molecules of gas m } Alternate form of ideal gas law: PV = nrt = M RT Mass per volume: m m: mass V = PM RT M: molar mass 11

13 Given 1% CO 2 at atmospheric pressure ( kpa) and 25 C ( K), calculate the following: Hint: } Molar mass of CO 2 = 44 g/mol; R = m3 Pa K mol ppm = ( 0.01)*10 6 =10 4 } } Partial pressure of CO 2 = 0.01* kpa = Pa Mass per volume = PM ( RT = Pa) ( 44 g/mol) = 18 g/m m3 Pa K mol ( K ) 12

14 } Nitrogen (N 2 ): 780,840 PPM } Oxygen (O 2 ): 209,460 PPM } Argon (Ar): 9,340 PPM } Carbon dioxide (CO 2 ): 394 PPM } Methane (CH 4 ): 1.79 PPM } Hydrogen (H 2 ): 0.55 PPM } Carbon monoxide (CO): 0.1 PPM } Ozone (O 3 ): PPM * See the full list here: 13

15 } Could you use any of the gas sensors for your rocket? Consider: Recall in dry air: Minimum detection level CO 2 : 394 PPM O Response time 3 : PPM How could you compensate for long response times? Heater voltage Sensitivity ratio between gases

16 Temp:28 RH:65% [O 2 ]:21% 15

17 Temp:20 RH:65% [O 2 ]:21% R L : 20 kω 16

18 } Air quality monitoring (CO 2, O 3, CO) } Smoke alarms (CO 2 ) } Mine and tunnel warning systems (CO 2, combustible gas ) } Greenhouses (CO 2 ) } Breathalyzer (Alcohol) } Automotive applications (O 2, CO 2 ) OxygenSensorDesign.aspx sustainable_mobility/co2_sensor_1.html 17

19 } Gas Sensor } Humidity Sensor } Pressure Sensor } Vibration Sensor 18

20 Relative humidity (RH) describes the amount of water vapor in a mixture of air and water vapor. RH = e w e * w 100% = partial pressure of water vapor saturated vapor pressure of water at the given temp e * W is the maximum water vapor that the air can hold without condensing ( ) and is f T,P

21 20

} Capacitive } Resistive } } } Honeywell HCH-1000 HIH-4010 EMD-4000 http://media.digikey.

22 } Capacitive } Resistive } } } Honeywell HCH-1000 HIH-4010 EMD %20Control%20PDFs/HCH-1000%20Series.pdf ?cur=USD 21

23 Capacitive RH sensor: } } } Dielectric constant of a polymer or inorganic material changes as it absorbs water vapor Dielectric constants: 80 (water) vs. 3.4 (polyimide) More water à higher capacitance C = ε A d Honeywell%20Sensing%20&%20Control%20PDFs/ HCH-1000%20Series.pdf 22

24 Resistive RH sensor: } } } } Electrical resistance of a material changes as it absorbs water vapor Typical materials: salts, conductive polymers Less sensitive than capacitive RH sensors Material properties also tend to depend both on humidity and temperature (in practice, must be combined with temperature sensor) 23

25 } What is the input range? } What is the output range? } What is the sensitivity? } What is the response time? 24

26 } Gas Sensor } Humidity Sensor } Pressure Sensor } Vibration Sensor 25

27 } Force-based Piezoresistive: ΔR Piezoelectric: ΔV Capacitive: ΔC } Others Resonance: ΔQ (damping) Thermal (Pirani gauge) Piezoresistive pressure sensor 26

28 } What is pressure? e.g. atmospheric pressure at sea level is kpa e.g. tire pressure gauge reads 0 PSI e.g. pressure drop for flow measurement } What kind of pressure do you want to measure? Absolute pressure sensor (compares to vacuum) Gauge pressure sensor (compares to ambient) Differential pressure sensor 27

29 Method #1: ΔP = ρg Δh Assumes density is constant over all height. Is this accurate? Method #2: Using the ideal gas law, ρ = P h mass = nm volume = nrt P PV = nrt = MP RT RT h ( ) = P 0 exp Mg M: Molar Mass n: Number of moles T: Temperature P: Pressure h: Altitude Accounts for changing density, but not temperature, with height 28

30 The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. M: Molar Mass n: Number of moles T: Temperature P: Pressure h: Altitude 29

31 Method #3: The image cannot be displayed. Your computer may not have enough memory to open the image, or the image may have been corrupted. Restart your computer, and then open the file again. If the red x still appears, you may have to delete the image and then insert it again. 30

32 Method #3: 31

33 32

} What is the input range? } What is the sensitivity? } What is the supply voltage? } What is the offset voltage? } What is the full scale output? } What is the output range?

34 } What is the input range? } What is the sensitivity? } What is the supply voltage? } What is the offset voltage? } What is the full scale output? } What is the output range? } Note: the fully integrated pressure sensor has gain stage and temperature compensation inside (signal conditioning is done already) 33

35 } Gas Sensor } Humidity Sensor } Pressure Sensor } Vibration Sensor 34

Examples: Piezoelectric films (ΔV) Strain gauges (ΔR) What happens when you pull on a piece of metal? metal foil strain gauge R = ρ L A http://www.digikey.com/scripts/us/dksus.dll?

36 Examples: Piezoelectric films (ΔV) Strain gauges (ΔR) What happens when you pull on a piece of metal? metal foil strain gauge R = ρ L A

37 } Full-scale range } Number of axes } Interface (analog, digital, pulse output) } Bandwidth ( Hz) } Power consumption (supply voltage)

38 Suggestion: Use the vibration sensor in the Op Amp Lab for your rocket 37

39 } Vibration Sensing in Washing Machine } Low Power Wakeup Switch } Car Alarms } Body Movement } Security Systems } Digital Cameras } iphone 38

40 (1) What are your science/engineering goals? (2) What sensors will you use to achieve your goals? - E80 website (Final Project) has a list of potential sensors (3) What circuits will you need? - Sensors need power - Voltage regulators - Sensor outputs need to interface with the data logger - Amplifiers - Buffers - Anti-aliasing filters 39

CHAPTER 1. MEASURES OF ATMOSPHERIC COMPOSITION

1 CHAPTER 1. MEASURES OF ATMOSPHERIC COMPOSITION The objective of atmospheric chemistry is to understand the factors that control the concentrations of chemical species in the atmosphere. In this book