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:
• Excessive 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.
• The software is outdated:
• Alterations to or creation of protocols are
very tedious
• Only users with great programming
knowledge are capable of working with it
Background
• Hypoxia (<21% O2) is a form of respiratory
distress; responses of the neuro-respiratory
system include:
• Hyperventilation and increased CO2 production
• Release of neurotrophins and
neurotransmitters in respiratory control
neurons1
• Hyperoxia (>21% O2) is widely studied
when used during critical postnatal
developmental periods:
• Impairs carotid body chemoreceptor growth
and function in rats2
• Impair the natural response to hypoxia during
adulthood in rats3
1. Baker et al., 2003 2. Fuller et al., 2002 3. Bavis et al., 2003
Background
• Hypoxia/Hyperoxia protocols differ
greatly:
• Intensity (percentage of O2)
• Type (Continuous or Episodic)
• Duration (Minutes, Hours, or even Days)
• Occurrence (Once, Daily, etc.)
• Significance and clinical applications:
• Association with SIDS
• Obstructive Sleep Apnea
• Recovery of some respiratory control
following incomplete spinal cord injury
Mass Flow Controllers (MFCs)
• Often aid in hypoxia
research
• Alter Oxygen
concentrations to
desirable levels for
testable consequences
• Automate gas flow
rates, thus gas
concentrations, to
desired levels
Mass Flow Controllers
• Desired 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
sensor
• A 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 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.
Current Gas Control System
Components of Current System
• Two Manual Flow
Controllers
• Four Analog Mass
Flow Controllers
Components of Current System
• Computer
controlled
Command Module
(HyperTerminal
Software)
• Four Chambers
Design Specifications
• Variable gas concentrations and flow
rates through a chamber
• Software controlled with an easy to
use interface and customizable
features
• Accurate gas delivery
• Uniform tubing resistance
• Low sound level
• Capability 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).
• After further research and client
communication, analog MFCs were
reconsidered.
• CMOSens® PerformanceLine MFC was seen as
the best.
• The optimal digital MFC was also changed to
the 100 Series Smart-Trak™, by Sierra
Instruments.
MFC Specifications
Product
Accuracy
Flow
Range
ANALOG
CMOSens®
PerformanceL
ine
Mass Flow
Controller
Price
Response
Time
$1079.00 US
+/- 0.8% of
reading at
10-100% of
full scale
0-5 slpm
+/- 0.7% of
reading +
0.3% full
scale
0-7 slpm
+/- 15V
Power:
$50.00 US
15 ms to
within +/2% of
setpoint
DIGITAL
Sierra 100
Series
Smart-Trak™
Mass Flow
Controller
$1370.00 US
2 seconds to
within +/2% of
setpoint
Software

Programming Module.
• 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.
• This module is 100% complete.
Programming Mode
Software

Operational Module.
• 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.
• Currently 75% complete because the
mass flow controllers have not been
order yet.
Operational Mode
Communication: FieldPoint
• Modular distributed
I/O system
• Flexible, expandable
network
• Dual-Channel analog
or digital modules
• Transmits flow setpoints to MFCs in
real-time
National Instruments
FieldPoint Network
MFC
Potential Problems
• Compatibility issues between different
manufacturer products.
• Incomplete protocol capabilities within the
LabView program.
• Program being designed may not be userfriendly to all lab techs needing to use it.
• With such rapidly changing technology,
the system design could become outdated
sooner than anticipated.
Future Work
• Integration of a third gas, CO2, into the
system.
• Improve design of rat testing chambers to
maximize accuracy of inspired gas.
• Addition of more chambers and respective
components for more elaborate protocols.
• 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:




John G. Webster, Advisor
Brad Hodgeman, Client
Adam Sweet, National Instruments
Paul Victorey
References
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