Exhaust Emissions Analyzer

Introduction

In a day when global CO2 levels are one of the greatest concerns of society, surprisingly few advances have been made in the field of portable CO2 emission analyzers. Such a product has the potential for tremendous marketability and could drastically change the way people view their cars.

Design

May08-25 Client: Ben Weatherman (National Instruments)Advisor: Dr. Arun Somani

Joshua Lichti, CprEJonathan Langford, CprE

Phil Nguyen, EEKet-Bing Yong, EE

Requirements

Plan

Implementation

Conclusion

ProblemNational Instruments asked Team May08-25 to design, implement, and test an exhaust emission sensor that could be used on a moving vehicle.

System Block DiagramThe exhaust emission analyzer system will take the output signal from the CO2 sensor circuit, interpret the data with the microcontroller, and display it on a user interface.

Operating EnvironmentThe system was designed to be able to generate valid, CO2 emission-level readings while being exposed to a wide range of environmental conditions:

• 0°C to 70°C• 0% to 80% humidity• rain, ice, and snow

User InterfaceThe user interface will display the level of CO2

concentration in the automobile’s exhaust emission for the user to see in real time.

Work BreakdownThe design team was composed of two Electrical Engineers and two Computer Engineers. The work was divided up as follows:

Electrical Engineers: System Hardware, Sensor Circuit, and PCB layoutComputer Engineers: System Software, LabVIEW Embedded, and Microcontroller

Resource Requirements• CO2 sensor chip • Parts for sensor circuit• Gold mirror• LabVIEW Embedded• Microcontroller

Non-Functional Requirements4. The software shall detect lost hardware and

display an error within 1 minute of the loss.5. The system shall function at a temperature

range of 0°C to 70°C.

Market SurveyFrom the market research found, wireless and

portable exhaust gas analyzers are available.

Prices range from $4000 to $5000, which is too expensive for a car owner. The goal of the design team was to build a portable exhaust analyzer at a much more affordable cost.

Functional Requirements1. The system shall contain a sensor to measure

CO2 emission from a moving automobile.2. The system shall contain a hardware device to

communicate information to a user interface.3. The system shall contain a microprocessor

that will run LabVIEW Embedded software to interpret and display the data.

DeliverablesThe completed exhaust emission analyzer project

will be composed of:• CO2 sensor circuit• CO2 measurement hardware device• CO2 level calculation LabVIEW software

The system consists of electrical and mechanical aspects, as well as a software interface.

MethodBuilding a compact exhaust sensor challenges for the team because most analyzers are bulky and require high power.

Input/Output SpecificationsInput to sensor circuit: Emission exhaust Input to MCU: Voltage between 0V and 5VOutput: CO2 percentage

Hardware SpecificationsSensor: up to 50% CO2, 0-50°C, <200mWMicrocontroller: 0-50°C, <200mW, >2 inputs

TestingComponent Testing

• Test all major components individually• Ensure power consumption and temperature specifications are met

System Testing• Test full circuit with multi-meter, then Data Acquisition Card• Vary temperature and concentration levels to ensure correct operation for all

environments.

Test ResultsComponent testing – SuccessSystem testing – In Progress

Team May08-25 successfully planned and designed an exhaust emission analyzer as requested by National Instruments.  The team also created a prototype of the system.  However, the team was not able to bring the prototype to full functionality.  

Functional components of the prototype:• Sensor circuit• Mirror and mirror stand• LabVIEW software

The electronics of the sensor are very sensitive to electrical and environmental change and getting the prototype to function properly under actual environment conditions will be something to work toward in the future.  Other possible, future improvements will include an air flow measurement unit in which the system will be able to calculate the percent of CO2 concentration as a function of time and a system to cool the exhaust air before it reaches the analyzer. 

Software SpecificationsDeveloped with NI LabVIEWWindows OS supportFilter and display real-time CO2 readings

User Interface SpecificationsGraphical display of CO2 value

+ReadInput()

InputProcesser

+ReadFile()+StartLogging()+StopLogging()

FileOps

+UpdateUI()

UserInterface

+FilterInput()

Filter

Mechanical Design

Mirror Stand and Mirror Holder

Circuit Schematic

PCB Layout

Software Class Diagram

Part Vendor Cost

Sensorchip CO2 ICX $ 150.00

Gold Mirror Edmund $ 40.00

Small Electrical Components Various $ 16.98

NI USB-6009 DAQ National Instruments $ 242.00

Phytec phyCORE®-ARM7/LPC2294 Phytec $ 300.00

Labor Breakdown13%

20%

12%

37%

18%

Planning

Design

Implementing

Testing

Documentation

Total Hours603.5

The configuration for the Wheatstone bridge allows for a 2 independent controlled sensing scheme. A voltage is applied across pin 6 and 22 which results in Joule heating of Element #1 (R3). The change in resistance for our purpose will come from the presence of gas which will exhibit itself as a change in temperature to the exposed Element.

The circuitry allows for a 2 pixel sensing scheme where the filament of the sensor is one leg of the bridge and a precision matched pair resistor network of 10K ohms is the bridge reference. A set point bias is set to adjust signal size, but the use of high signal increases aging of the device. The final Op Amp amplifies the signal with depending on R16, with the Gain = 1 + 49.9K/R16.

Project SchedulePlanning – Due 11/30/08Design – Due 11/30/08Implementation – Due 3/22/08Testing – Due 4/8/08Documentation – Due 4/8/08

RisksCreating the system involved several risks:

• Moisture build-up• Vibration disturbance• Temperature outside range specified• Degradation of device from repetitive high concentration of CO2

Non-functional components of the prototype:• Sensor's ability to accurately measure

CO2 in all environments• Optics and electronics of the analyzer