Testing
Three tests were used to make sure that the RMS G-Meter was accurate.Test 1: Flipping
When the meter is turned on, the unit zeros itself. By flipping the unit onto its side, it will no longer detect 1G because the acceleration will be in a different direction. This causes the display to show -1G.
 G-Meter zeroed |  G-Meter on side experiencing -1G as anticipated |
Test 2: Rotating arm
The rotating arm was integral to making sure that the meter was able to perform accurate readings all the way to 5G. For this, we constructed an arm from a car window motor (due to its high torque and low price of $17). The arm consists of a holster for the G-Meter, a 2.4GHz wireless video camera with a custom made battery pack, and counter-weights to keep the arm steady. The wireless video camera was necessary because the device spins at a rate that's too fast for reading the display.
By measuring how fast the motor was moving and how long the arm was, acceleration was calculated using acceleration = velocity^2 / radius. To measure how fast the motor was running, we used a thin piece of metal held stationary in a spot that would just barely nick the end of arm that held the G-Meter. Using a microphone, we recorded the sound wave:
After the sound wave was acquired, Matlab was used to detect the peak sound level that was created when the arm would nick the metal. This allowed us to find the distance between the peaks and calculate the speed of the motor. It worked amazingly well, our largest deviation between nicks was 0.009 seconds away from the normal.
video of the rotating arm
Test 3: Oscillator
Instrumented Sensor Technology provided us with an oscillating machine to test the RMS features of the G-Meter. This machine worked by moving an arm up and down. The speed of the arm and the length that it moves is calculated. From this, the following equations were used to calculate the acceleration:
x(t) = Asin(wt)
a(t) = X''(t) = -Aw2sin(wt)
arms = .707*A w^2
Oscillator without the G-Meter attached. The G-Meter sits above the washers on the right.
