The common mode voltage range that the iSIC data logger can handle is 0-2.5V. A differential voltage, even though the difference is within the range of 0-2.5V, still may have individual voltages less than 0V or exceeding 2.5V. In this case, the signal is cut off at 0V or 2.5V which causes a faulty reading.
For example, if the common mode voltage of both signals is negative when measured with respect to AGND then both signals will be cut off at 0V, resulting in a differential voltage of 0V. One way to rectify this problem is to using single-ended mode. This FAQ goes through the steps to change from differential to single-ended mode.
1. Connect the negative signal to AGND on the iSIC terminal strip and the positive signal to one of the iSIC analog input channels such as AD0 or AD1.
2. Open iChart with a current project.
3. Right click on the sensor in the navigation window and select Property.
4. From the channel drop down menu, select the analog input channel that the positive signal is wired to.
5. Click OK to finalize the change.