Some SCXI modules also have internal channels. These are physical channels that are not accessible from an I/O connector. To measure the signals present at these internal physical channels, use them to create virtual channels. The SCXI-1100, SCXI-1102, SCXI-1120, SCXI-1121, SCXI-1122, and SCXI-1125 modules have an internal physical channel called _cjTemp channel. It is the cold-junction compensation channel for measuring the temperature at the connector for thermocouples.
The SCXI-1112 has internal channels _cjTemp0, _cjTemp1, _cjTemp2, _cjTemp3, _cjTemp4, _cjTemp5, _cjTemp6, and _cjTemp7. These are the cold-junction compensation channels for each analog input channel on the SCXI-1112.
The SCXI-1520 has eight pairs of internal channels _pPos0 and _pNeg0 through _pPos7 and _pNeg7. These channels read back the excitation on the corresponding analog input channel. The pPos half of the pair is the positive side of the excitation, and the pNeg half is the negative side of the excitation. The real excitation value is the pPos value minus the pNeg value.
The SCXI-1521/B has 24 voltage excitation internal channels _Vex0 through _Vex23. These channels read back the excitation on the corresponding analog input channel. In addition, the SCXI-1521/B has 24 pairs of internal channels _IexPos0 and _IexNeg0 through _IexPos23 and _IexNeg23. The current through a sensor connected to channel x is the _IexPosx value minus the _IexNegx value.