Filter Acceleration as Inclination Angle

If this option is selected, a real-time filter is applied so that the inclination of the sensor is computed and the data is stored and plotted as angles in the range [-90, 90] degrees.

It is recommended that the sensor be calibrated before using this option for accurate angle measurements.

The algorithm used for computing the filtered values is as follows:

1. The data are low-pass filtered with a 5 Hz finite-impulse-response (FIR) filter, using a Blackman window and a filter kernel size of 255.  The latency introduced by this filter is approximately 1.72 seconds when operating at the low data rate (2000 Hz EMG / 148 Hz ACC) and approximately 0.86 seconds when operating at the high data rate (4000 Hz EMG / 296 Hz ACC).  This filter removes the dynamic impact component of the acceleration.  Note that changes in inclination that happen at a rate of 5 Hz or greater will be attenuated by this filter.
2. The data are converted to tilt along three axes according to the following equations, and the output is expressed as degrees in the range [-90, 90].

            

Interpret each filtered axis as follows:

Channel Name	Filtered Channel Interpretation
ACC X	The angle between the X-axis and the horizontal plane.
ACC Y	The angle between the Y-axis and the horizontal plane.
ACC Z	The angle of the Z-axis relative to gravity.

Because the arctangent is a nonlinear function, the sensitivity (accuracy) changes throughout the range of measurement.  For easy comparison when using this option, the overall latency introduced by the impact and inclination real-time filters is identical.  The latency may be corrected for with the TIME SHIFT calculation in EMGworks analysis.

This option is available to all sensors that contain acceleration data channels [Standard Trigno, Snap Lead, Spring Contact, EKG]