Artifact Filter Dialog
The Artifact Filter dialog controls the action (if any) to take when the signal is above or below the specified levels. Used by the Average and Smoothing commands.
The low limit is primarily used for excluding dropout signals from average calculations. The default value, and 'Set to zero and skip' should be suitable for many cases. The dropouts may be from loss of signal due to tissue movement or gaps in the erythrocytes passing through the capillary.
The high limit is primarily used for excluding noise spikes generally caused by laser reflections from the tissue surface. This is not as effective as the low level filter, since it is difficult to distinguish between the sharp rise from the cardiac pulse and noise. Using an absolute value on small sections at a time may be most appropriate.
To apply only the artifact filter to a trace, Smooth the trace using a zero time constant.
Artifact Limit
Enter a value here for the limit of acceptable values. Either absolute values or percent of the last valid value can be used.
Absolute Value
Set the limit to an absolute value. Units of the currently active trace in the current view are used. Any values above or below this will be considered as artifact. Action to be taken is set by the Filter Action.
Percent
The percentage of the last valid value is used as the artifact limit. All values above or below this level are treated as artifact.
Filter Action
No Action
Ignore this artifact limit and calculate all points.
Repeat last valid value
The last value within the artifact limits is substituted for points falling outside the artifact limits.
Set to zero & skip
If the output of the operation is a trace then the result for any points falling above or below the limits will be set to zero.
In the Smoothing operation the artifact value is ignored and does not influence the smoothed trace. (No compensation for the missing time is made).
For the Average calculations the point is simply ignored.