Gas Pressure Meter (Engineering World Health) Advisor: Prof. Ken Gentry Client: Prof. John Webster, Engineering World Health Engineering World Health Team Members: Ksenija Bujanovic- BSAC Claire Edlebeck- Communications Mike Oldenburg- Team Leader Chris Webster- BWIG

Background Information Background on Engineering World Health Background on Engineering World Health EWH Design Program EWH Design Program – EWH specifications – Submission of design – Approval => money for prototype – Mass-production Limiting factors Limiting factors cost cost

Problem Statement Gas Pressure Meter Gas Pressure Meter – Engineering World Health (EWH) – Different gasses – Compatibility with machines Generally found inside machines (anesthesia, ventilators, etc.) Generally found inside machines (anesthesia, ventilators, etc.) – Ours will be external

Design Constraints Measure pressure of medical gas (i.e. O 2, CO 2, Anesthetic gasses). Measure pressure of medical gas (i.e. O 2, CO 2, Anesthetic gasses). Measure in the range of -35 mmHg to 75 mmHg. Measure in the range of -35 mmHg to 75 mmHg. Digital interface. Digital interface. Minimum accuracy is within 10% of true value, though 1% would be ideal. Minimum accuracy is within 10% of true value, though 1% would be ideal. Reusable. Reusable. Flexible connection capabilities (still unknown what machines they will be incorporated with). Flexible connection capabilities (still unknown what machines they will be incorporated with). Cost less than $2 in quantities of 500 or $5 in quantities of 20. Cost less than $2 in quantities of 500 or $5 in quantities of 20.

Current Tech (Basic Principles) Manometer Manometer U shaped column filled with water or mercury. U shaped column filled with water or mercury. Pressure in one side results in difference in level (x). Pressure in one side results in difference in level (x). Great for analog, not ideal for digital. Great for analog, not ideal for digital. Bourdon Gauge Bourdon Gauge Coiled tube that expands under pressure. Conjoined with a gear train, can rotate a dial relative to pressure. Again, great for analog, less effective for digital All images taken from Wikipedia.org

Current Tech (cont.) Strain Gauge Strain Gauge – As the object is deformed, electrical resistance is changed and produces a voltage difference. – Change in resistance usually measured with a Wheatstone bridge then related to gauge factor. Lessons In Electric Circuits copyright (C) Tony R. Kuphaldt

Design 1- Propeller Insert an axial fan into a tube with known diameter. Insert an axial fan into a tube with known diameter. Voltage output related to speed of rotation and force of the gas on the blades. Voltage output related to speed of rotation and force of the gas on the blades. Through calibration and the use of known air pressures, we can create a curve that will reveal an unknown pressure based on voltage output. Through calibration and the use of known air pressures, we can create a curve that will reveal an unknown pressure based on voltage output.

Pros and Cons of Design 1 Pros Pros –Inexpensive –Simple calculations –Components can be easily obtained Cons Cons –Requires flow –Requires calibration –Malfunction might obstruct airway

Design 2- Piezoelectric Material Responds to mechanical stimulus with a change in voltage Responds to mechanical stimulus with a change in voltage

Pros and Cons of Design 2 Pros Pros – More accurate than propeller design – Safety – Easier circuit design compared to propeller Cons Cons – Only responds to changes in pressure (static conditions could not be measured) – Expensive

Design 3- Strain Gauge Responds to strain with a change in voltage over one of the resistors in the circuit Responds to strain with a change in voltage over one of the resistors in the circuit Lessons In Electric Circuits copyright (C) Tony R. Kuphaldt

Pros and Cons of Design 3 Pros Pros – Commercially available (pressure transducers, strain gauges) – Very accurate – Can measure static pressures – Inexpensive Cons Cons – Requires calibration – More components that can malfunction

Design Matrix DesignPiezoelectricPropeller Strain Gauge Patient Safety 868 Size334 Cost4810 Ease of production 334 Durability354 Client requirements 6610 Total273140

Future Work Design the Wheatstone bridge circuit Design the Wheatstone bridge circuit Design the interface between the strain gauge and the digital display Design the interface between the strain gauge and the digital display Write a proposal for EWH based on the design Write a proposal for EWH based on the design Use current strain gauge to build a prototype for testing Use current strain gauge to build a prototype for testing Design testing procedure and calculate a calibration curve Design testing procedure and calculate a calibration curve Improve accuracy of the prototype Improve accuracy of the prototype Lower cost of device Lower cost of device

QUESTIONS?