P18352: Sandia Passive Vacuum Detection Team B
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Systems Design

Table of Contents

Content linked here should go in the Systems Level Design Documents directory. This directory is pre-populated with a variety of templates that are designed to help you through this phase of the design.

Team Vision for System-Level Design Phase

Summarize:

During this phase we plan on using our customer requirements to begin initial design of the sensor. This will be our chance to come up with a few different ideas and determine which one is the best. By the end of this phase we plan on having an idea on which design we would like to pursue.

During this phase we worked to prove that the concept was feasible and developed some basic concept ideas that could help us continue our design. This phase proved to be very difficult given the small magnitude of force change on any object.

Functional Decomposition

Functional Decomposition

Benchmarking

There are many different kinds of mechanical pressure switches available on the market. Diaphragms, piezoelectric actuators, pistons, springs, and snap-action switches were studied and considered for our application.

The various mechanical switches that were found on the market may present good starting points for our concept development. The lowest-reading switch found utilizes a piston/spring system, and is capable of reading down to 15 mm Hg. Given that the customer requires pressure detection of less than 0.1 mm Hg with a mechanical switch, it is clear that the desired switch does not currently exist, at least as a product that may be purchased off the shelf.

The only switch that is capable of measuring low vacuum pressure is the piezoelectric actuator, but this switch requires the use of motor controllers and computer software. The customer has affirmed that the switch must not rely on electronic components to measure pressure.

It is unclear whether or not some of these switch designs can withstand the 20-27 G-Force requirement presented by the customer. The manufacturer of the snap-action switch was the only one to claim that the sensor could falsely actuate when subjected to vibration. The other switch manufacturers could not comment on their product's ability to withstand vibrations or intense G-Forces. It is also noteworthy that none of these switches are rated to function in the customer's temperature requirement of -70 degrees Celsius.

A summary of the benchmarking research is presented below:

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Concept Development

Magnetic Popper

Magnetic Popper

Lever Piston

Lever Piston

Diaphram

Diaphram

Valve Train

Valve Train

Feasibility: Prototyping, Analysis, Simulation

The feasibility of a diaphragm system was analyzed by assuming a circular plate with a uniform load. Using this analysis, we find that a Kapton diaphragm would deflect over an eighth of an inch when subjected to vacuum on one side, and atmospheric pressure on the other side.

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Morphological Chart and Concept Selection

Morphological Table

Morphological Table

Concept Selection

  1. Sensitivity: The system has to be extremely sensitive to small changes in pressure which relate to an even smaller change in force.
  2. Cost: The system has to fall within our budget of $1000.
  3. Size: The system has to fit within the specified size and will also need to be as light as possible.
  4. Rigidity: The system has to be strong enough to withstand forces during launch which include high lateral g forces and vibrations.
  5. Resetablility: For testing purposes the system needs to be reset with ease so that the customer can confirm it is working properly.
  6. Usable Force / Motion: The design has to have enough force through it motion to actually activate the switch. A system stretched to its limits may not be able to exert enough force to activate the switch.
  7. Ease of Manufacturing: The design has to be simple enough to manufacture in a small amount of time so that ample time can be dedicated to testing it and confirming that it is calibrated well.

A decision matrix was created that rates each design against these selection criteria. Each team member gave the design a rating between 1-5. 1 is the lowest rating and 5 is the best. Whichever design received the highest rating would be selected for further research and design. For our project, we will be using the Diaphragm for proof of concept and then design a system similar to the magnetic popper for more precision.

Decision Matrix

Decision Matrix

Systems Architecture

System Architecture

Designs and Flowcharts

Initial Systems Concept

Initial Systems Concept

Risk Assessment

Project Risks

Project Risks

Plans for next phase

By the next review we plan on having a single design ready to be developed. The team will work to use engineering to prove that the design can work on paper. Some items may be fabricated or ordered and preliminary testing may take place.


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