LabChart does not support reading in text data collected at different sampling rates; however, it is possible to specify a global sampling rate during the import process. If your file has multiple signals collected at different sampling rates you have one of two options: (1) up or down sample your various channels to the same sampling rate during the export process, (2) re-record your data at a common sampling rate.
If you have further questions or concerns about this, please contact your local Technical Support Representative by completing the online form located HERE.