P18351: Sandia Passive Vacuum Detection Team A
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Systems Design

Table of Contents

Team Vision for System-Level Design Phase

During the system-level design phase our team will work to determine a high level design to address our customer and engineering requirements addressed during the previous problem definition phase. Many concepts for the system operation characteristics will be examined and the most feasible will be selected for further analysis and prototyping.

In this phase, NAMASTe was able to generate a handful of different potential sub-system designs to solve our most pressing design constraints. Using a rating system, we chose the sub-system designs that scored highest. From there, we conceptualized the best combinations of possible solutions to generate a couple feasible system concepts. Using another grading scale, we compared our system design concepts and chose the best one to pursue. This resulted in the "pressure-piston" system design concept shown below.

Functional Decomposition

Purpose

Define the total list of functions and subfunctions, based on the Customer and Engineering Requirements, that must be delivered by the final design. This establishes the need for specific concepts necessary to deliver the overall objectives of the project

public/Photo Gallery\functional Decomposition Tree.PNG

Benchmarking

There were no mechanical vacuum detecting switches currently on the market which met all of the design criteria for this project, but several pressure sensing switch devices were found from which to derive design ideas. On top of these, a syringe will be used in the prototyping phase as a benchmarking reference for the final design.

Vacuum Switch Switch Specifications

P581 Vacuum Pressure Switch

p581
  • 43.5 mmHg to 381 mmHg detection
  • Entirely mechanical operation
  • 1 million life cycles
  • Brass housing with nitrile diaphragm
  • 300 stainless steel spring
  • 2.15”x1.77” cylinder
  • 3A inductive @ 24VDC
  • 15°F to 250°F capability with nitrile diaphragm

NoShock 300 Pressure Switch

300
  • 15x10^3 mmHg to 15x10^4 mmHg detection
  • Mechanical or electrical operation
  • Zinc plated steel construction
  • 30g shock, 10g vibration handling
  • 0.1A at 30VDC

117 Series Pressure Switch

117
  • 762 mmHg to 1.81x10^5 mmHg detection
  • Mechanical activation of snap switch
  • Includes tamper-resistant set point lock
  • Die cast powder coated aluminum enclosure with stainless steel fittings
  • 15g for 10ms shock handling, 2.5g, 5-500Hz vibration handling
  • 5A at 28VDC
  • -120°F to 540°F oprating range

Concept Development

Purpose

Generate new concept options or combinations that can potentially exceed the benchmark concepts
Concept Development (placeholder image - to be updated)

Concept Development (placeholder image - to be updated)

Feasibility: Prototyping, Analysis, Simulation

Prototyping: A Syringe with atmospheric pressure will be tested in a vacuum chamber under controlled pressures. The resulting expansion lengths of the syringe will be recorded and verified against our hand calculations to ensure accuracy of derived equations. After baseline syringe testing is done, a small scale prototype will be build in order to observe effects in the required pressure range.

Analysis:

Hand Calculations for Expansion Length

Hand Calculations for Expansion Length

Looking at the System, it can be seen that the pressure acting on the plunger is going to be equal to the difference between the internal and external pressures of the system. Doing a force balance we can see that as long as the difference in pressures multiplied by the area of the plunger is greater than the static force of friction, the plunger will move. Using this principal we can more accurately design our system by controlling its internal pressure. Manipulating this equation we can determine the internal system pressure required so that the system only moves once a specific atmospheric pressure is hit. To determine the expansion length of the plunger we turn to the universal gas law. Assuming and isothermal process we can set the equation equal to constant. This will allow us to set the initial pressure/volume relationship equal to any pressure/volume in the future of the system. Manipulating this property we can derive our equation for system expansion at any external pressure. By combining these two concepts we get our final equation, which will give the minimum expansion length required in an optimal system.

Morphological Chart and Concept Selection

Four design alternatives were generated by selecting one solution for each of the determined functions from the chart presented in the Concept Development section above. These design alternatives are presented below.

Note

For clarity and consistency, each concept alternative will be given a name corresponding to a function selection that is unique to that alternative. Each alternative will be referred to by the solution proposed for the pressure sensing function.
Design Alternatives

Design Alternatives

Concept Selection

A number of selection criteria were developed in order to evaluate each design alternative. One design alternative was selected as the datum to which all other alternatives were compared to, based on the selection criteria. The alternatives were evaluated only on if they would adhere to the given selection criteria better, worse, or the same as the datum alternative. The design alternative with the most favorable results compared to the first datum was then used as the datum for a second comparison to ensure that it was indeed our best option when compared to all other alternatives.
Pugh Charts for Concept Selection

Pugh Charts for Concept Selection

This consists of two elements:

The real value in this step of the process is not the comparison matrix you generate to compare your concepts, but the analysis and discussion you do to support your evaluation.

Systems Architecture

Purpose

  1. Ensure flow of energy, info, material and structural forces as intended.
  2. Define subsystem functions, envelopes and interfaces.
Diagram demonstrating main design forces in consideration

Diagram demonstrating main design forces in consideration

Table explain force diagram and showing their relation to one another

Table explain force diagram and showing their relation to one another

Designs and Flowcharts

Purpose

Define a high-level view of the elements required to build and operate the entire system
Initial Concept Design, View 1

Initial Concept Design, View 1

Initial Concept Design, View 2

Initial Concept Design, View 2

Initial Concept Design, View 3

Initial Concept Design, View 3

Risk Assessment

Risk Assessment

Risk Assessment

Design Review Materials

Plans for next phase

We are aiming to complete subsystem design for our primary subsystems. We also are targeting to complete preliminary integration and collaboration between our subsystems.


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