Gnomon Shadow Test Result

Test plan

Task Description: Measure the shadow cast by the gnomon pin onto the gnomon base at various angles to confirm it can measure shadows to the specified accuracy.

Completed: Feb 9, 2021

Conducted and documented by: Ali

Resources Required: EM Gnomon, EM sample plate, EM payload structure, bright light source, dark room, turn table, protractor

Verification Activities: V-PLD-0260, V-PLD-0270, V-PLD-0280

Pass Criteria: Confirm that the gnomon can:

1) Measure solar incidence angles of up to 50 degrees from the gnomon pin vector;

2) Measure solar incidence angles to at least a 5 degree resolution;

3) Measure the rotational resolutions to at least a 15 degree resolution.

Results:

Solar incidence resolution:

After setting up the test apparatus, we rotate the apparatus so that the sample plate is parallel to the incoming light. The protractor shows -31.5 degree. Then, we slowly rotate the turn table CCW until the gnomon pin's shadow just touches the edge of the gnomon. Now, the protractor shows 16 degree. Then, we slowly rotate the turn table CCW in 5 degree increments, until the structure shades the gnomon pin. The following table shows where the shadow is on the gnomon at each interval.

Rotational resolutions:

After setting up the test apparatus, we rotate the apparatus so that the structure's +X face is normal to the light source. Then, we slowly rotate the turn table CCW in 5 degree increments until the gnomon pin's shadow is just covered by the EM structure's shadow. The following table show where the shadow is on the gnomon at each interval.

Conclusion and Discussion:

According to the test results, it can be confirmed that

We can measure solar incidence angles of up to 53 degrees from the gnomon pin vector.
We can measure solar incidence angles to at least a 5 degree resolution.
We can measure the rotational resolutions to at least a 10 degree resolution.

However, there are sometimes that we haven't the degree resolution according to the test criteria. The reasons are

It's hard to read because of black gnomon base.
Gnomon pin's length might not be accurate, because it was cut by wire cutter.

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