The NI 9203 can be used to measure the current into your system. In fact, the NI 9203 can be used to measure current at any point in your system, just like an ammeter. The COM terminal of the NI 9203 does not always have to be connected to ground. The figure below shows a setup where the NI 9203 is being used to measure the current into a system. In this case, the COM terminal is connected to the positive input to your instrument.