Vibration Tool

The Vibration tool facilitates the analysis of small periodic motions such as may be present in various machine components. To begin a vibration analysis check Enable and drag the yellow bordered region of interest over the area of the image to be analysed. Note that the clip must be either Playing or Stopped, not Paused.

Area Slider

The area of interest can be modified by changing the Area slider. Try to arrange that the area of interest is mostly all in motion as high contrast stationary features inside this region can affect the measurement, although useful information can still be obtained even then.

Range Slider

The Range slider should be set according to the amount of motion present; it approximately determines the maximum amount of movement in pixels between frames that can be tolerated. If unknown, start high and work downwards if the signal is too noisy. If the amplitude suddenly changes when dropping down this means that the motion is outside the current set range and the slider should be moved back up a level.

Chart Scaling

Chart scaling can be set with the Scale slider or can be automatically determined by checking Autoscale. If Max only is also checked then the chart will only ever scale upwards when autoscaling. This can be useful when repeating or refining a measurement where constant rescaling is confusing and the history of the measurement can be seen in better context.

Charting

The charting overlay consists of a vectorscope on the left and a time plot on the right. The vectorscope shows the movement in the X and Y axes of the image, with the time plot showing the history of the motion projected along the yellow vector axis of the vector scope. To change the projection axis angle, move the Axis rotary dial. For instance to look at only the horizontal vibration component set the Axis to 90° and the time chart will reflect this. The usual use for this control is to measure the amplitude of the dominant axis of vibration by aligning the yellow vector with the dominant oscillation visible on the vectorscope.

In addition to displacement, the chart can also show velocity or acceleration, selected using the Plot pulldown. Noise in the velocity and acceleration plots can be improved at the expense of frequency response by selecting a Filter option from the pulldown. Currently the only option is a Savitzky-Golay of order 5 (SG5).

To view the frequency spectrum of the vibration check FFT. The vertical scale is in dB relative to the currently selected Scale setting and the timebase is determined by the recorded FPS, i.e. time in the real world.

Lowpass and Highpass Filter

Lowpass and highpass filtering can be applied to the measurement to improve SNR or filter out unwanted frequencies. The FFT chart will reflect the frequency profiling applied here, but since the Q of the applied filter is quite moderate (0.707) the rolloff may look rather subtle on the dB scale.

The timebase length for the time chart can be changed using the Span slider and the FFT length using the FFT Length slider. Larger FFT lengths will increase the resolution of the spectrum at the expense of a longer settling time.

By default the units of displacement are in pixels, but this can be changed to mm or m using the Units pulldown. In order for this to be accurate calibration has to be performed as described in the Measure section.