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

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

Problem Motivation Current mass flow controllers are too inaccurate:Current mass flow controllers are too inaccurate: Excessive drift occurs causing the client to have to constantly tweak the flow rates to obtain desired concentrationsExcessive drift occurs causing the client to have to constantly tweak the flow rates to obtain desired concentrations An undesirable variable is added from manual flow controllers in place to regulate equal flow to subsequent chambers.An undesirable variable is added from manual flow controllers in place to regulate equal flow to subsequent chambers. The software is outdated:The software is outdated: Alterations to or creation of protocols are very tediousAlterations to or creation of protocols are very tedious Only users with great programming knowledge are capable of working with itOnly users with great programming knowledge are capable of working with it

1. Baker et al., Fuller et al., Bavis et al., 2003Background Hypoxia (<21% O 2 ) is a form of respiratory distress; responses of the neuro-respiratory system include:Hypoxia (<21% O 2 ) is a form of respiratory distress; responses of the neuro-respiratory system include: Hyperventilation and increased CO 2 productionHyperventilation and increased CO 2 production Release of neurotrophins and neurotransmitters in respiratory control neurons 1Release of neurotrophins and neurotransmitters in respiratory control neurons 1 Hyperoxia (>21% O 2 ) is widely studied when used during critical postnatal developmental periods:Hyperoxia (>21% O 2 ) is widely studied when used during critical postnatal developmental periods: Impairs carotid body chemoreceptor growth and function in rats 2Impairs carotid body chemoreceptor growth and function in rats 2 Impair the natural response to hypoxia during adulthood in rats 3Impair the natural response to hypoxia during adulthood in rats 3

Background Hypoxia/Hyperoxia protocols differ greatly:Hypoxia/Hyperoxia protocols differ greatly: Intensity (percentage of O 2 )Intensity (percentage of O 2 ) 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 following incomplete spinal cord injuryRecovery of some respiratory control following incomplete spinal cord injury

Mass Flow Controllers (MFCs) Often aid in hypoxia researchOften aid in hypoxia research Alter Oxygen concentrations to desirable levels for testable consequencesAlter Oxygen concentrations to desirable levels for testable consequences Automate gas flow rates, thus gas concentrations, to desired levelsAutomate gas flow rates, thus gas concentrations, to desired levels

Mass Flow Controllers Desired input gas is divided into two different pathsDesired input gas is divided into two different paths A large fraction flows into a bypass; remaining portion (usually 5%) of gas goes into the thermal sensorA large fraction flows into a bypass; remaining portion (usually 5%) of gas goes into the thermal sensor A pair of heating coils measure the change in temperature from the beginning to the end of the tubeA pair of heating coils measure the change in temperature from the beginning to the end of the tube

Mass Flow Controllers The downstream coil, composed of thermal sensitive wiring, has a higher temperature, and thus more resistance.The downstream coil, composed of thermal sensitive wiring, has a higher temperature, and thus more resistance. The coils are part of a Wheatstone bridge circuit that has an output voltage proportional to that of the change in the two resistances.The coils are part of a Wheatstone bridge circuit that has an output voltage proportional to that of the change in the two resistances. Ultimately, the bridge is used for the resistance to voltage conversion, which can be further calibrated to a relative flow rate.Ultimately, the bridge is used for the resistance to voltage conversion, which can be further calibrated to a relative flow rate.

Current Gas Control System

Components of Current System Two Manual Flow ControllersTwo Manual Flow Controllers Four Analog Mass Flow ControllersFour Analog Mass Flow Controllers

Components of Current System Computer controlled Command Module (HyperTerminal Software)Computer controlled Command Module (HyperTerminal Software) Four ChambersFour Chambers

Design Specifications Variable gas concentrations and flow rates through a chamberVariable gas concentrations and flow rates through a chamber Software controlled with an easy to use interface and customizable featuresSoftware controlled with an easy to use interface and customizable features Accurate gas deliveryAccurate gas delivery Uniform tubing resistanceUniform tubing resistance Low sound levelLow sound level Capability for further expansionCapability for further expansion

MFC Decision Process At mid-semester, three of the best digital mass flow controllers were chosen, with a top choice (Advanced Energy – Aera® Mach One).At mid-semester, three of the best digital mass flow controllers were chosen, with a top choice (Advanced Energy – Aera® Mach One). After further research and client communication, analog MFCs were reconsidered.After further research and client communication, analog MFCs were reconsidered. CMOSens® PerformanceLine MFC was seen as the best.CMOSens® PerformanceLine MFC was seen as the best. The optimal digital MFC was also changed to the 100 Series Smart-Trak™, by Sierra Instruments.The optimal digital MFC was also changed to the 100 Series Smart-Trak™, by Sierra Instruments.

MFC Specifications ProductAccuracy Flow Range Price Response Time ANALOG CMOSens® PerformanceL ine Mass Flow Controller +/- 0.8% of reading at % of full scale 0-5 slpm $ US +/- 15V Power: $50.00 US 15 ms to within +/- 2% of setpoint DIGITAL Sierra 100 Series Smart-Trak™ Mass Flow Controller +/- 0.7% of reading + 0.3% full scale 0-7 slpm $ US 2 seconds to within +/- 2% of setpoint

Software Programming Module. Programming Module. Reads protocol specifications from the user, such as flow rate, oxygen percentages, various times, etc.Reads protocol specifications from the user, such as flow rate, oxygen percentages, various times, etc. Upon completion, the module writes the data to a file that was specified by the user.Upon completion, the module writes the data to a file that was specified by the user. This module is 100% complete.This module is 100% complete.

Programming Mode

Software Operational Module. Operational Module. This Module loads a previously written protocol and sends the instructions to the mass flow controllers.This Module loads a previously written protocol and sends the instructions to the mass flow controllers. Once the protocol is loaded, the user can choose which chambers to use in the experiment.Once the protocol is loaded, the user can choose which chambers to use in the experiment. Currently 75% complete because the mass flow controllers have not been order yet.Currently 75% complete because the mass flow controllers have not been order yet.

Operational Mode

Communication: FieldPoint Modular distributed I/O systemModular distributed I/O system Flexible, expandable networkFlexible, expandable network Dual-Channel analog or digital modulesDual-Channel analog or digital modules Transmits flow set- points to MFCs in real-timeTransmits flow set- points to MFCs in real-time

MFC National Instruments FieldPoint Network

Potential Problems Compatibility issues between different manufacturer products.Compatibility issues between different manufacturer products. Incomplete protocol capabilities within the LabView program.Incomplete protocol capabilities within the LabView program. Program being designed may not be user- friendly to all lab techs needing to use it.Program being designed may not be user- friendly to all lab techs needing to use it. With such rapidly changing technology, the system design could become outdated sooner than anticipated.With such rapidly changing technology, the system design could become outdated sooner than anticipated.

Future Work Integration of a third gas, CO 2, into the system.Integration of a third gas, CO 2, into the system. Improve design of rat testing chambers to maximize accuracy of inspired gas.Improve design of rat testing chambers to maximize accuracy of inspired gas. Addition of more chambers and respective components for more elaborate protocols.Addition of more chambers and respective components for more elaborate protocols. Incorporating a calibration mode into LabView for easily adjustable changes.Incorporating a calibration mode into LabView for easily adjustable changes.

Acknowledgements We would like to thank the following people for their help throughout the semester: We would like to thank the following people for their help throughout the semester: John G. Webster, Advisor John G. Webster, Advisor Brad Hodgeman, Client Brad Hodgeman, Client Adam Sweet, National Instruments Adam Sweet, National Instruments Paul Victorey Paul Victorey

References Advanced Energy Industries, Co. Multi-Gas Selection Capability of a DMFC. 6 February 2004.Advanced Energy Industries, Co. Multi-Gas Selection Capability of a DMFC. 6 February Agilent Technologies. Agilent VEE Pro February 2004Agilent Technologies. Agilent VEE Pro February 2004 Baker, T. L., Mitchell, G. S., Episodic but not continuous hypoxia elicits long-term facilitation of phrenic motor output in rats. J. Physiol., 521.9: 215-9Baker, T. L., Mitchell, G. S., Episodic but not continuous hypoxia elicits long-term facilitation of phrenic motor output in rats. J. Physiol., 521.9: Bernard, E. Controlling the Flow- Digitally. 14 February 2004Bernard, E. Controlling the Flow- Digitally. 14 February 2004 Boer, H. J. Precision Mass Flow Metering For CVD Applications. 6 February 2004.Boer, H. J. Precision Mass Flow Metering For CVD Applications. 6 February Chizinsky, G. Multi-Gas Selection Capability of a Digital Mass Flow Controller. 2 March 2004 Chizinsky, G. Multi-Gas Selection Capability of a Digital Mass Flow Controller. 2 March 2004 DATAQ Instruments. XControls Bring Applications to Life. 16 February 2004DATAQ Instruments. XControls Bring Applications to Life. 16 February 2004 Feldman, J. L., McCrimmon, D. R., Neural Control of Breathing. Fundamental Neuroscience, second edition., Academic Press, San Diego Feldman, J. L., McCrimmon, D. R., Neural Control of Breathing. Fundamental Neuroscience, second edition., Academic Press, San Diego Fuller, D. D., Johnson, S. M., Olsen, E. B., Mitchell, G. S., Synaptic Pathways to Phrenic Motoneurons Are Enhanced by Chronic Intermittent Hypoxia after Cervical Spinal Cord Injury. J. Neurosci., 23(7): Fuller, D. D., Johnson, S. M., Olsen, E. B., Mitchell, G. S., Synaptic Pathways to Phrenic Motoneurons Are Enhanced by Chronic Intermittent Hypoxia after Cervical Spinal Cord Injury. J. Neurosci., 23(7): Kinkead, R., Zhan, W., Prakish, Y. S., Bach, K. B., Sieck, G. C., Mitchell, G. S., Cervical dorsal rhizotomy enhances serotonergic innervation of phrenic motoneurons and serotonin-dependent long-term facilitation of respiratory motor outputs in rats. J. Neurosci., 18(20): Kinkead, R., Zhan, W., Prakish, Y. S., Bach, K. B., Sieck, G. C., Mitchell, G. S., Cervical dorsal rhizotomy enhances serotonergic innervation of phrenic motoneurons and serotonin-dependent long-term facilitation of respiratory motor outputs in rats. J. Neurosci., 18(20): Mitchell, G. S., Johnson, S. M., Plasticity in Respiratory Motor Control, Neuroplasticity in respiratory motor control. J. Appl. Physiol. 94: Mitchell, G. S., Johnson, S. M., Plasticity in Respiratory Motor Control, Neuroplasticity in respiratory motor control. J. Appl. Physiol. 94: National Instruments, LabVIEW. Austin, TXNational Instruments, LabVIEW. Austin, TX National Instruments. Serial Communication General Concepts. 27 February 2004National Instruments. Serial Communication General Concepts. 27 February 2004 Qualiflow. MFC Principles: A basic course. 14 February 2004 Qualiflow. MFC Principles: A basic course. 14 February 2004 Sierra Instruments. High Performance Mass Flow Meters and Controllers. 28 February 2004 Sierra Instruments. High Performance Mass Flow Meters and Controllers. 28 February 2004 Sweet, A. Presentation. Topics In LabVIEW. 3 March 2004Sweet, A. Presentation. Topics In LabVIEW. 3 March 2004 Zabka, A. G., Behan, M., Mitchell, G. S., 2001.Zabka, A. G., Behan, M., Mitchell, G. S., Long term facilitation of respiratory motor output decreases with age in male rats. J. Physiol : Long term facilitation of respiratory motor output decreases with age in male rats. J. Physiol :