The implementations for current and voltage measurements are slightly different and require different adapters for the NI 9218 as described below:
1. Current Measurement with a Powered Sensor
To perform a current measurement you must use the NI 9983D/L/F Current Shunt Adapter and enable the DAQmx Channel Property Nodes AI.Excit.Src and AI.Excit.Val as shown below:

2. Voltage Measurements with a Powered Sensor
To perform a voltage measurement with internal excitation you must select the +/-65 mV or +/-16 V measurement range/mode and use the NI 9982D Screw Terminal Adapter. You have the option of utilizing the DAQmx Create Channel (AI Custom Voltage with Excitation) VI or a property node in conjunction with the DAQmx Create Channel (AI Voltage) VI as shown below:
