P17341: Harris Near-Zero CTE Test Apparatus
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Customer Handoff & Final Project Documentation

Table of Contents

Team Vision for Final Demo and Handoff

At the previous design review, a major shortcoming was discovered: after upgrading the size and strength of the levitation electromagnet, the Hall effect sensor intended to control magnetic levitation in the sample coupon was unable to function in the strong magnetic field. With this in mind, the team agreed to split the twin objectives of the project into two parts: 1) demonstrate feasibility of magnetic levitation of a sample coupon, and 2) measure CTE of a coupon sample. Thus, in order to demonstrate the fulfillment of these two objectives, validation testing was performed on both functions of the device individually. Without the Hall effect sensor or some other sensing device, it was not possible to accomplish both, since without reference position data on the top of the sample, it cannot be known if a change in the reading of the bottom position sensor was caused by expansion of the sample or oscillation of the coupon+clamp as a whole.

Engineering Requirements vs Performance

Engineering requirements vs Performance

Engineering requirements vs Performance

Project Bill of Materials and Upgrade Components

Material purchases & budget

Material purchases & budget

BOM color coding

BOM color coding

Items by week

Items by week

Item owners and critical dates

Item owners and critical dates

Due to size, only snapshots of the total BOM are shown. The full document can be accessed here.

Since the budget and timeframe of the project did not allow for the best components to minimize error in the CTE test system, the following are presented as alternatives to minimize error. The effect of these upgrades on error minimization is shown in "Error Analysis" section below.

Subsystem upgrades & overall path forward

Subsystem upgrades & overall path forward

Test Results Summary

Test Plan S1: Electromagnetic Strength

Electromagnet test procedure

Electromagnet test procedure

Electromagnet test results

Electromagnet test results

Test Plans S2, S3, and S6: Control System Stability (Large Scale Prototype)

Control test procedure

Control test procedure

Control test procedure

Control test procedure

Control test procedure

Control test procedure

Control system initialization

Control system initialization

Control system tracking

Control system tracking

Control system longevity

Control system longevity

Levitation example

Levitation example

Test Plan S4: Sensor Calibration

Calibration procedure

Calibration procedure

Calibration test results

Calibration test results

Test Plan S5: Danger of Shock

Shock test results

Shock test results

Coefficient of Thermal Expansion Testing

With the sample coupon and clamp held in a static position in the frame's slot fixure, CTE testing was carried out on the sample. The thermal shroud was used to provide heat flux to the coupon, and the shroud temperature control thermocouple was connected to the coupon directly by aluminum tape. This is because controlling the shroud temperature directly caused the coupon to take too long to reach equilibrium temperature. As a downside, the thermal shroud experienced a much greater maximum temperature, causing a potential safety issue.

Temperature testing was carried out on the sample coupon, with distance data collected from the capacitive sensor. At this point it was noted that the capacitive sensor signal suffered from heavy noise, which was magnified when the heating shroud was active.

It was theorized that the noise was caused by the 120V 60Hz AC power from the wall socket that powered the thermal shroud. This is because the temperature controller only uses a "two-prong" connection to the wall socket, and is not grounded. Therefore even when the relay switch is open and the shroud does not pass current (and heat up), it still experiences a voltage potential fluctuation from the one connected terminal. (The exact mechanism that results in the noise being transferred to the capacitive sensor signal is unknown, however).In order to alleviate this noise, the sample coupon was allowed to heat up and reach a steady value, then the controller was unplugged and the sample was allowed to cool back down to ambient temperature. By disconnecting the shroud from the wall entirely, the noise witnessed in the cap sensor output was reduced substantially.

Raw results- Test 1

Raw results- Test 1

Raw results- Test 2

Raw results- Test 2

Raw results- Test 3

Raw results- Test 3

CTE Results

CTE Results

An additional thermocouple was placed on the capacitive sensor mounting flange, in order to demonstrate that the flange experiences insignificant temperature rise throughout the test.

Simultaneous Test

A test was run with the magnetic levitation and heating systems active at the same time. Despite the noise induced from the heating shroud, the sample was still able to achieve stable levitation. However, as discussed previously, without the use of a second sensor at the top of the structure, it is not possible to subtract out rigid body motion that may occur as the sample heats and lengthens. Therefore, it is not possible to measure CTE while levitating the sample with the current setup.
Raw results- Thermal shroud & maglev system active

Raw results- Thermal shroud & maglev system active

Error Analysis

Error components

Error analysis - current components

Error analysis - current components

Total error (by root-sum-squares method): 2.38 x10^-6 in/in/deg F

Error analysis - upgraded components

Error analysis - upgraded components

Total error (by root-sum-squares method): 7.55 x10^-7 in/in/deg F

Note that these error values, while oftentimes informed by the actual results obtained in the lab, are still theoretical. Unaccounted for/underrated error sources may arise in actual testing, especially as the sensitivity of the device increases.

Error comparison

Error comparison

Error comparison

Error of upgraded system

Error of upgraded system

The spreadsheet with error calculations can be found here.

Risk and Problem Tracking

Project Risks

Risk management remained unchanged from the previous phases, as "risks" were considered more as vague, conceptual problems, not concrete issues faced by the team.

Risk Management list

Risk Management list

Risk Explanation

Risk Explanation

Project Problem Tracking

Critical problems and solutions

Critical problems and solutions

Major problems (1/2)

Major problems (1/2)

Major problems(2/2)

Major problems(2/2)

Final Project Documentation

Hypothetical Plans for Future Work

Action items the team would like to take, provided we had an additional three-week phase following this review (also goals for future iterations of this project):

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