RMS Displacement Meter is a free Android application developed by keuwlsoft in the Utilities & Tools category. This app is designed to measure displacement by double integrating the acceleration from your device's linear acceleration sensor. It is important to note that not all devices with an accelerometer will have the linear acceleration sensor capability required for this app to work.

To ensure accurate measurements, RMS Displacement Meter applies a drift reduction algorithm to remove any DC component and then measures the AC displacement using a Root Mean Square (RMS) value or performs a Fast Fourier Transform (FFT) to obtain the frequency spectrum. The app provides a gauge to show the RMS displacement in the X, Y, or Z directions, as well as its magnitude. Additionally, there is an RMS graph that displays the gauge readings over time.

The lower display of the app shows time series data or a FFT from it, with peak indicators for the frequency spectrum. Users can save graph data to a file and choose their preferred units of measurement, including centimeters, millimeters, meters, inches, or feet.

For example, users can move their device in a circle along two of its axes and observe two sinusoidal traces 90 degrees out of phase in the time series graph. This allows them to determine the rotation frequency in the frequency spectrum and obtain an estimate of the diameter of the circle from the gauge or its corresponding graph when set to peak-to-peak mode in the settings.

It is important to note that linear acceleration sensors may vary in sampling speed, resolution, and accuracy from one device to another, so the app provides indications only.

RMS Displacement Meter is a powerful tool for measuring alternating displacements and offers a range of features to assist users in obtaining accurate measurements of displacement on their Android devices.