P18351: Sandia Passive Vacuum Detection Team A
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Integrated System Build & Test

Table of Contents

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Team Vision for Integrated System Build & Test Phase

Summarize: In this phase, our team set out to complete the following:
  1. Pressure testing for adjustment of fine pressure activation
  2. Finalize vibration testing requirements and have test completed
  3. Determine feasibility of translating Shock testing into constant g-force testing
  4. Build a final design

We were able to accomplish:

  1. Pressure testing determined that our system needs more adjustment
  2. Scheduled Vibration testing
  3. Found information on translating shock testing to constant G-force testing
  4. Second prototype is in the process of being made

Final Design

Final Design Assembly

Final Design Assembly

Final Design Assembly

Final Design Assembly

Test Results Summary

System Activation Testing

A full scale bell jar system was used to drop pressure down to 10^-2-10^-4 Torr in order to simulate usage conditions. The location of the switch to the diaphragm was adjusted and switch activation was monitored.

Contact Switch Assembly Setup

Contact Switch Assembly Setup

Inside Bell Jar Setup

Inside Bell Jar Setup

Test Plan:

  1. Set switch on L-Bracket mounts
  2. Use a combination of washers (.033in) and nuts (0.093in) to move mount closer/further to diaphragm
  3. Use pass-through in bell jar to connect switch contact to monitor for a closure
  4. Run vacuum pump and monitor for activation
  5. If switch activated before vacuum chamber dial starts to read (aprox.10^-2torr), remove some offset material
  6. If switch does not activate when the vacuum chamber has reached its minimum pressure (~10^-4torr), add some offset material

Results from Testing

Through various tests it was found that with 0.121" of offset our switch would prematurely activate and at 0.0975" of offset there was no activation. The issue arising out of this is that with nuts and washers the smallest amount of offset that we can vary is 0.033". This required us to find a new method for controlling the switch displacement. The new method determined is mounting the switch on a 4-40 threaded rod. This allows use to control displacement to within 0.003125" using 8th of a rotation of the rod as a displacement measurement.

Updated Diaphragm Test Stand

Updated Diaphragm Test Stand

Updated Test Plans:

  1. Set Diaphragm Assembly to initial distance from switch
  2. Measure and record initial distance of diaphragm to switch
  3. Use pass-through in bell jar to connect switch contact to monitor for a closure
  4. Run vacuum pump and monitor for activation
  5. If switch activated before vacuum chamber dial starts to read (aprox.10^-2torr), turn lever backward by 1/8th of the "Clock Face"
  6. If switch does not activate when the vacuum chamber has reached its minimum pressure (~10^-4torr), turn lever forward by 1/8th of the "Clock Face"
  7. Record Trial distances and Results

Environmental Testing Simulation

Before subjecting our physical system to the vibration testing, we wanted to ensure that our design was theoretically robust enough to withstand the test. In order to do so, the system was modeled in ANSYS. The various environmental tests were then modeled to ensure that results were on a reasonable order of magnitude.

Due to software license limitations, the model had to be simplified in order to simulate. The main mounting bracket and the c-clamps were kept, while the cylindrical section that contains the diaphragm and switch was modeled as a rigid point mass, constrained to the edges of the c-clamp. While this will not give us the dynamics of this part of the assembly, we believe that it is safe to assume as a rigid body when compared to the other brackets.

Simplified Model for Simulation in ANSYS

Simplified Model for Simulation in ANSYS

Launch Acceleration

From the initial problem statement, it is known that the system must survive a 27g acceleration force due to launch.
27g Vertical Acceleration Loading

27g Vertical Acceleration Loading

Vibration

Prior to conduction the random vibration simulation, a modal analysis was performed to determine the mode shapes and natural frequencies of the system out to 1.5x the maximum frequency that will be applied during the random vibration (2000Hz). The first 3 modes are shown below, and are consistent with what the intuitive mode shapes of the system would be. Please click the images to enlarge.
Mode 1, 260hz

Mode 1, 260hz

Mode 2, 775hz

Mode 2, 775hz

Mode 3, 1059hz

Mode 3, 1059hz

Provided from the customer, the PSD of the vibration of the rocket is approximated as a constant 0.005 [G^2/Hz] from 20-2000 Hz. For simulation, our assembly will be subjected to this spectrum on each primary axis independently.

X Axis

X Axis

Y Axis

Y Axis

Z Axis

Z Axis

Risk and Problem Tracking

Risks

Risks

Problem Tracking

Problem Tracking

Functional Demo Materials

Plans for next phase

For the next phase, team NAMASTe plans to have completed testing with Delphi and be ready to ship the switch to the customer. Regardless, time has been allotted for changes in case of failure during testing. At that point in time, a separate version will then be prepared for use at Imagine RIT while the final one is shipped to the customer.

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