Hello Raspberry Shake Community,
I have a Raspberry Shake 4D (RE038), and recently, I attempted to compare its performance with the IMV VP 7000L by manually shaking both devices. I conducted the test at a frequency of 1 Hz with a peak-to-peak displacement of 10 inches. This corresponds to an amplitude of 5 inches (0.127 meters). For the Raspberry Shake, I performed vertical (up-down) shaking and recorded both velocity from the geophone and acceleration from the accelerometer. Below is a comparison between the theoretical calculations and the recorded data:
Theoretical Values:
We know that:
- Displacement,
x=AsinâĄ(Ďt)=AsinâĄ(2Ďft)
- Maximum Displacement:
A = 0.127 meters
- Maximum Velocity:
AĎ=AĂ2Ďf=0.127Ă2Ă3.1416Ă1= 0.79797 meters/second = 798 mm/second
- Maximum Acceleration:
AĎ²=AĂ(2Ďf)²=0.127Ă(2Ă3.1416Ă1)²= 5.013 meters/second²
Recorded Data:
I collected 10 seconds of data and plotted the results:
- Plot 1: Velocity data from the geophone (EHZ channel)
- Plot 2: Acceleration data from the accelerometer (ENZ channel)
Data Conversion Code:
I used the following Python code (ObsPy library) to convert counts to physical units:
Converting Counts to Acceleration:
import obspy
# Load the inventory file
inv = obspy.read_inventory('RE038.xml') # Inventory file of AM.RE038
# Load and read the MiniSEED file
file = "./AM.RE038.00.ENZ.D.2024.323"
st = obspy.read(file)
# Attach response and remove it to convert to acceleration
st.attach_response(inv)
st.remove_response(output="ACC") # Convert to acceleration (m/s²)
Converting Counts to Velocity:
import obspy
# Load the inventory file
inv = obspy.read_inventory('RE038.xml') # Inventory file of AM.RE038
# Load and read the MiniSEED file
file = "./AM.RE038.00.EHZ.D.2024.323"
st = obspy.read(file)
# Attach response and remove it to convert to velocity
st.attach_response(inv)
st.remove_response(output="VEL") # Convert to velocity (m/s)
Observations and Questions:
I understand that manually shaking the devices is not a precise method. However, the accelerometerâs recordings align closely with the theoretical value of approximately 5 m/s². In contrast, the geophoneâs velocity readings show a maximum amplitude of around 40 mm/s (considering around 80mm/s peak to peak), which is significantly lower than the expected theoretical value.
Given these results, I would like to seek your guidance on the following:
- Is there an issue with my data conversion process from counts to physical units?
- Are there any other factors or aspects that I might be overlooking in this experiment?
Thank you for your time and assistance. I look forward to your valuable insights.
Best regards,
Rahat Ibn Nabi
RSH.RE038.2024-11-30T04_51_10.logs.tar (2.9 MB)
AM.RE038.00.EHZ.D.2024.323 (4.6 MB)
AM.RE038.00.ENZ.D.2024.323 (4.8 MB)
RE038.xml (18.3 KB)