Taking Custom Voltage Measurements with the PXIe-4339

The PXIe-4339 supports taking regular (non-ratiometric) voltage measurements using an AI Voltage task. In addition, as of NI-DAQmx 14.5, the PXIe-4339 can perform custom voltage measurements while providing voltage excitation, for example, when using DC powered sensors that return a non-ratiometric voltage. To enable this type of measurement, configure the DAQmx Create Virtual Channel VI to AI Custom Voltage with Excitation mode.

Setting the use excitation for scaling input to False will prevent the PXIe-4339's ADCs from scaling the measured voltage ratiometrically to the excitation voltage.

Setting the use excitation for scaling input to True, will enable the PXIe-4339 to use the excitation value that the user sets with the DAQmx driver for scaling the ratiometric input. The device will not use the voltage present on the remote sense lines for scaling as it does when providing internal excitation. Thus, while the driver will support using external excitation for ratiometric measurements, this is not a recommended configuration.

The table below covers each possible combination of AI channel type, voltage excitation source input value, and use excitation for scaling input value. The cases highlighted will throw DAQmx errors, and the reasons for the errors are described in the Use Case and Notes column of the table.

Note An RM-4339 is required to select external excitation.