Hello Vassil,
In some resistance ranges (below 20 Ohms or so) the PXI-4130 (Source measure unit, SMU) and some of our DMM's like the 4071 and 4072 offer comparable accuracy for resistance measurements. There are two approaches you can take:
1. Define a particular range of resistance you want to measure and choose the absolute most accurate device.
2. Decide on an acceptable level of accuracy and then choose the SMU or DMM depending on what other applications you have. Since a SMU servers a completely different purpose than a DMM you may want to take this into consideration when choosing a device.
In making this decision you can use the accuracy specified in each manual. You will need to know the approximate resistance value you want to measure in order to calculate the accuracy. For the PXI-4071 DMM (most accurate) see page 2. For the PXI-4072 DMM (allows inductance and capacitance measurements) see page 4. For the PXI-4130 SMU see page 2--you'll need to use both the current output accuracy and the voltage reading accuracy to calculate the resistance accuracy. Another option, if your DUT can sustain high currents (1-2 Amps) would be to get both the SMU to source a precision current and a DMM to read the voltage (for very low resistances this may provide the best accuracy).
In general it is not necessary to source 1 Amp to measure low resistances. If for some reason you require this high current then you will need to get the SMU rather than a DMM because the DMMs cannot provide this high current. Unless there are specific circumstances that require high current I would recommend considering a DMM as well. If you'd like to speak with a technical representative at National Instruments you can use the contact information at www.ni.com/contact.
I hope this helps, and have a great day!
Cheers,
Brooks
