Curious how the Frogwatch actually works? In this article series, we’ll walk through the entire measurement chain step by step and explain how Frogwatch arrives at the final measurement results.
Determining Orientation
The Frogwatch vibration sensor records vibrations in three directions: X, Y, and Z. Unlike many other devices, these directions are not fixed. Instead, the meter automatically detects how you have positioned it. How does that work?
The Frogwatch is based on a (MEMS) accelerometer. This type of sensor measures accelerations: besides vibrations, it also measures gravitational acceleration (gravity). Here on Earth, that’s a constant value of about 9.81 m/s².
By filtering out the effect of vibrations (i.e., averaging over a long enough period), we are left with a constant value in each of the three measurement directions, caused by gravity. The larger this value, the more that direction aligns with gravity: the direction with the largest value points downward!
Once the device knows which sensor axis points most towards gravity (downward), the X/Y/Z axes are assigned according to a fixed pattern:
- The vertical direction is called Z
- The direction along the wall is called Y
- The direction perpendicular to the wall is called X
Level or Not?
Because the Frogwatch Sensor knows the proportion of gravity measured on each axis, the system can use trigonometry to calculate how level the device is placed. Before the measurement starts, the meter performs a short self-test. If the meter is tilted by more than 3 degrees, a warning appears on the dashboard.
Why level the device?
Although it is not strictly necessary, we still recommend mounting the device as straight as possible. This ensures that:
- Vertical vibrations on the Z-axis: By mounting the device straight, vertical vibrations are measured as much as possible on the Z-axis. This prevents vibrations from being distributed over the other axes, which improves accuracy and interpretation.
- Uniformity in measurements: All Frogwatch sensors within a project measure in the same direction, which is essential for comparability.
- Reproducibility: Accurate repetition of measurements is possible, for example during zero measurements or long-term analyses.
How straight is straight enough?
In practice, "by eye" mounting is often sufficient. A deviation of more than 1 degree is easily noticeable visually, even without tools like a spirit level.