# Digital Multimeters (DMMs) and Precision DC Sources

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## Query SMU source voltage when in current mode?

I have a few SMUs (PXIe-4138, 4139, 4141, 4144, 4145, 4154 etc). When I run these instruments in current-controlled mode, I usually record the current, the set current and the sense voltage, as documented in https://nimi-python.readthedocs.io/en/driver_readme/index.html. Is there a way to record the source voltage in addition to the sense voltage?

Thanks!

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## Re: Query SMU source voltage when in current mode?

When you source current, why would that last configured value for source voltage matter?

Santhosh
Soliton Technologies

Finding it hard to source NI hardware? Try NI Trading Post
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## Re: Query SMU source voltage when in current mode?

I'd like to record the power dissipation in several parts of the circuit. Right now it's easy to calculate the power dissipation between the SMU voltage sense leads. I was about to set up a DMM to measure the voltage in a different location of the circuit (closer to the SMU), but  I figured if I know the voltage across the SMU current source, it would be almost as good as having an additional DMM, as I know that the voltage drop from the SMU current source to where I would connect the DMM is negligible.

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Accepted by topic author lfbsvsfbsapruwiq890

## Re: Query SMU source voltage when in current mode?

Okay, if you want to know the voltage drop due to the force leads, all you have to do is, switch to local sense, now the SMU will measure the voltage at its terminal instead of the DUT.

Santhosh
Soliton Technologies

Finding it hard to source NI hardware? Try NI Trading Post
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## Re: Query SMU source voltage when in current mode?

Great, exactly what I was looking for!

Thanks a lot!

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## Re: Query SMU source voltage when in current mode?

I tested it and it works on a PXIe-4154, as expected. However, a PXIe-4141 uses remote sense, even when set to local sense (I made a test circuit with a resistor in the source leads, and even when set to local, that resistance was not sensed). The documentation mentions that not all devices support local sense. According to the PXIe-4141 specifications, it supports local sense, but it does not work. There is no mention of local sense in the PXIe-4154 documentation, but it seems to work. Is there a list of SMUs that are known to support local sense?

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