If the normal precautions of warming and zeroing the spirometer prior to use do not prevent drift in the recorded flow signal (as pictured below), a software drift correction can be applied with the LabChart Spirometry Extension to remove baseline drift from any future flow data.
To access this feature, left mouse click on the flow channel's title bar, and select the "Spirometry Flow..." option from the Channel Calculation drop down menu that appears. The Spirometry Flow dialog will now open. In this dialog, select the Drift Correction checkbox, and click on the OK button.
The Drift Correction will now be applied to all future flow data when it is recorded. For the correction to work properly each data block must begin and end with at least 10 data points representing zero air flow, otherwise the Spirometry Volume calculation will not function correctly. This feature removes the signal drift as follows, the first and last 10 points in a flow data block are averaged, and a linear baseline interpolated between them, making the corrected flow zero at both the start and end of the block. If any point is too far from zero (more than 2.5% of full range), the correction is not applied.
For further technical assistance with this or any other issue, please contact ADInstruments Technical Support by clicking HERE.