It shouldn't really be necessary to worry about saving the two directly with relation to each other, when I encountered this problem I simply saved the desired data as two seperate channels, assuming your current is going to be incrementally developed you can just save the voltage and knowing the start value and increment for the current rebuild the curve later from this. Or possibly just save both the voltage and current they will appear plotted against time in the inbuilt TDMS viewer but you should be able to extract them as pure arrays of data at a later date as you wish.
[EDIT] Ok I reread that and bothered myself, moral of the story, just save the Voltage and current data as two different channels and extract later, that will basically treat the values as independent arrays.
