AbstractAbstract

A mass flow controller network was A mass flow controller network was made more user-friendly by the made more user-friendly by the creation of a LabView software creation of a LabView software program. In addition, extensive program. In addition, extensive research of commercial MFC types research of commercial MFC types yielded potential models that will yielded potential models that will inevitably produce more accurate inevitably produce more accurate results. results.

Problem StatementProblem Statement

The purpose of this project is to The purpose of this project is to design a system that can create a design a system that can create a reproducible and accurate gaseous reproducible and accurate gaseous environment with the capability of environment with the capability of oscillating between various oscillating between various concentrations of oxygen and concentrations of oxygen and nitrogen inducing states of hypoxia nitrogen inducing states of hypoxia or hyperoxia. or hyperoxia.

Problem MotivationProblem Motivation• Current mass flow controllers are too Current mass flow controllers are too

inaccurate:inaccurate:• Excessive drift occurs causing the client to Excessive drift occurs causing the client to

have to constantly tweak the flow rates to have to constantly tweak the flow rates to obtain desired concentrationsobtain desired concentrations

• An undesirable variable is added from An undesirable variable is added from manual flow controllers in place to manual flow controllers in place to regulate equal flow to subsequent regulate equal flow to subsequent chambers.chambers.

• The software is outdated:The software is outdated:• Alterations to or creation of protocols are Alterations to or creation of protocols are

very tediousvery tedious• Only users with great programming Only users with great programming

knowledge are capable of working with itknowledge are capable of working with it

1. Baker et al., 2003 2. Fuller et al., 2002 3. Bavis et al., 20031. Baker et al., 2003 2. Fuller et al., 2002 3. Bavis et al., 2003

BackgroundBackground• HypoxiaHypoxia (<21% O (<21% O22) is a form of respiratory ) is a form of respiratory

distress; responses of the neuro-respiratory distress; responses of the neuro-respiratory system include:system include:

• Hyperventilation and increased COHyperventilation and increased CO22 production production• Release of neurotrophins and Release of neurotrophins and

neurotransmitters in respiratory control neurotransmitters in respiratory control neuronsneurons11

• HyperoxiaHyperoxia (>21% O (>21% O22) is widely studied when ) is widely studied when used during critical postnatal developmental used during critical postnatal developmental periods:periods:

• Impairs carotid body chemoreceptor growth Impairs carotid body chemoreceptor growth and function in ratsand function in rats22

• Impair the natural response to hypoxia during Impair the natural response to hypoxia during adulthood in ratsadulthood in rats33

BackgroundBackground

• Hypoxia/Hyperoxia protocols differ greatly:Hypoxia/Hyperoxia protocols differ greatly:• Intensity (percentage of OIntensity (percentage of O22))• Type (Continuous or Episodic)Type (Continuous or Episodic)• Duration (Minutes, Hours, or even Days)Duration (Minutes, Hours, or even Days)• Occurrence (Once, Daily, etc.)Occurrence (Once, Daily, etc.)

• Significance and clinical applications:Significance and clinical applications:• Association with SIDSAssociation with SIDS• Obstructive Sleep ApneaObstructive Sleep Apnea• Recovery of some respiratory control Recovery of some respiratory control

following incomplete spinal cord injuryfollowing incomplete spinal cord injury

Mass Flow Controllers (MFCs)Mass Flow Controllers (MFCs)

• Often aid in hypoxia Often aid in hypoxia researchresearch

• Alter Oxygen Alter Oxygen concentrations to concentrations to desirable levels for desirable levels for testable consequencestestable consequences

• Automate gas flow Automate gas flow rates, thus gas rates, thus gas concentrations, to concentrations, to desired levelsdesired levels

Mass Flow ControllersMass Flow Controllers• Desired input gas is Desired input gas is

divided into two divided into two different pathsdifferent paths

• A large fraction flows A large fraction flows into a bypass; into a bypass; remaining portion remaining portion (usually 5%) of gas goes (usually 5%) of gas goes into the thermal sensorinto the thermal sensor

• A pair of heating coils A pair of heating coils measure the change in measure the change in temperature from the temperature from the beginning to the end of beginning to the end of the tubethe tube

Mass Flow ControllersMass Flow Controllers

• The downstream coil, composed of thermal sensitive wiring, The downstream coil, composed of thermal sensitive wiring, has a higher temperature, and thus more resistance. has a higher temperature, and thus more resistance.

• The coils are part of a Wheatstone bridge circuit that has an The coils are part of a Wheatstone bridge circuit that has an output voltage proportional to that of the change in the two output voltage proportional to that of the change in the two resistances. resistances.

• Ultimately, the bridge is used for the resistance to voltage Ultimately, the bridge is used for the resistance to voltage conversion, which can be further calibrated to a relative conversion, which can be further calibrated to a relative flow rate.flow rate.

Current Gas Control SystemCurrent Gas Control System

Components of Current SystemComponents of Current System

• Two Manual Flow Two Manual Flow Controllers Controllers

• Four Analog Mass Four Analog Mass Flow Controllers Flow Controllers

Components of Current SystemComponents of Current System

• Computer Computer controlled controlled Command Module Command Module (HyperTerminal (HyperTerminal Software)Software)

• Four ChambersFour Chambers

Design SpecificationsDesign Specifications

• Variable gas concentrations and flow Variable gas concentrations and flow rates through a chamberrates through a chamber

• Software controlled with an easy to Software controlled with an easy to use interface and customizable use interface and customizable featuresfeatures

• Accurate gas deliveryAccurate gas delivery• Uniform tubing resistanceUniform tubing resistance• Low sound levelLow sound level• Capability for further expansionCapability for further expansion

MFC Decision ProcessMFC Decision Process

• At mid-semester, three of the best digital At mid-semester, three of the best digital mass flow controllers were chosen, with a top mass flow controllers were chosen, with a top choice (Advanced Energy – Aera® Mach One).choice (Advanced Energy – Aera® Mach One).

• After further research and client After further research and client communication, analog MFCs were communication, analog MFCs were reconsidered. reconsidered. • CMOSens® PerformanceLine MFC was seen as the CMOSens® PerformanceLine MFC was seen as the

best. best. • The optimal digital MFC was also changed to the The optimal digital MFC was also changed to the

100 Series Smart-Trak™, by Sierra Instruments.100 Series Smart-Trak™, by Sierra Instruments.

MFC SpecificationsMFC SpecificationsProductProduct AccuracyAccuracy Flow Flow

RangeRangePricePrice Response Response

TimeTime

ANALOGANALOG

CMOSens® CMOSens® PerformancePerformanceLineLine

Mass Flow Mass Flow ControllerController

+/- 0.8% of +/- 0.8% of reading at reading at 10-100% of 10-100% of

full scalefull scale

0-5 slpm0-5 slpm$1079.00 US$1079.00 US

+/- 15V +/- 15V Power:Power:

$50.00 US$50.00 US

15 ms to 15 ms to within +/- 2% within +/- 2%

of setpointof setpoint

DIGITALDIGITAL

Sierra 100 Sierra 100 Series Smart-Series Smart-Trak™ Mass Trak™ Mass Flow Flow ControllerController

+/- 0.7% of +/- 0.7% of reading + reading + 0.3% full 0.3% full

scalescale

0-7 slpm0-7 slpm $1370.00 US$1370.00 US 2 seconds to 2 seconds to within +/- 2% within +/- 2%

of setpointof setpoint

SoftwareSoftware

Programming Module.Programming Module.• Reads protocol specifications from the Reads protocol specifications from the

user, such as flow rate, oxygen user, such as flow rate, oxygen percentages, various times, etc.percentages, various times, etc.

• Upon completion, the module writes the Upon completion, the module writes the data to a file that was specified by the data to a file that was specified by the user.user.

• This module is 100% complete.This module is 100% complete.

Programming ModeProgramming Mode

SoftwareSoftware

Operational Module.Operational Module.• This Module loads a previously written This Module loads a previously written

protocol and sends the instructions to protocol and sends the instructions to the mass flow controllers.the mass flow controllers.

• Once the protocol is loaded, the user Once the protocol is loaded, the user can choose which chambers to use in can choose which chambers to use in the experiment.the experiment.

• Currently 75% complete because the Currently 75% complete because the mass flow controllers have not been mass flow controllers have not been order yet.order yet.

Operational ModeOperational Mode

Communication: FieldPointCommunication: FieldPoint

• Modular distributed Modular distributed I/O systemI/O system

• Flexible, expandable Flexible, expandable network network

• Dual-Channel analog Dual-Channel analog or digital modulesor digital modules

• Transmits flow set-Transmits flow set-points to MFCs in points to MFCs in real-timereal-time

MFCNational Instruments FieldPoint Network

Potential ProblemsPotential Problems

• Compatibility issues between different Compatibility issues between different manufacturer products.manufacturer products.

• Incomplete protocol capabilities within the Incomplete protocol capabilities within the LabView program.LabView program.

• Program being designed may not be user-Program being designed may not be user-friendly to all lab techs needing to use it.friendly to all lab techs needing to use it.

• With such rapidly changing technology, With such rapidly changing technology, the system design could become outdated the system design could become outdated sooner than anticipated. sooner than anticipated.

Future WorkFuture Work

• Integration of a third gas, COIntegration of a third gas, CO22, into the , into the system.system.

• Improve design of rat testing chambers to Improve design of rat testing chambers to maximize accuracy of inspired gas.maximize accuracy of inspired gas.

• Addition of more chambers and respective Addition of more chambers and respective components for more elaborate protocols.components for more elaborate protocols.

• Incorporating a calibration mode into Incorporating a calibration mode into LabView for easily adjustable changes. LabView for easily adjustable changes.

AcknowledgementsAcknowledgements

We would like to thank the following We would like to thank the following people for their help throughout the people for their help throughout the semester:semester:

John G. Webster, AdvisorJohn G. Webster, Advisor Brad Hodgeman, Client Brad Hodgeman, Client Adam Sweet, National InstrumentsAdam Sweet, National Instruments Paul VictoreyPaul Victorey

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