PXI-4130 draws current when output is disabled

[GS]

I have a battery connected to the output of a PXI-4130 (SMU) to draw current from the battery. The problem is that the SMU still draws current (about 5 mA) when the output is disabled (verified by the light on the front panel). I assumed that disabling the output would keep that from happening. Did I make a bad assumption or is something wrong? I actually have two SMUs and they both do this (one draws more current than the other).

George

[PBear]

Hi George,

Can you confirm this behavior when using the DC POWER Soft Front Panel and not LabVIEW code? Also, how are you confirming the current draw, is it measured from an external source or are you reading from the current sense for the channel? I'm just trying to get a bit more information about the setup.

Thanks

[GS]

The SMU is tied up for a bit so I can't confirm it with the DC Power soft panel. 

I measured the current draw with an external DMM. I don't think it could be measured with the current sense from the channel since the output is disabled.

I take it this doesn't sound normal?

George

[PBear]

Hi George,

Almost everytime I troubleshoot interesting problems, I almost always use a test/soft front panel. It limits assumptions and puts most of the ownage onto the hardware. It's also sometimes one of the quickest ways to learn the functionality or specs of a device without searching through pages of information. When the SMU becomes available, try confirming this behavior using the soft front panel and I will do the same on my end with an in-house 4130. As far as I know, disabling the output of a channel should act as you said above.

[JeremyDC]

Hello George!

Actually, when you do a 'disable' using NI-DCPower, the channel 1 output of the PXI-4130 is configured for a 20mA current limit.  If you'd like to completely disconnect the SMU from your system, an external relay could be used (you could probably power it using channel 0 of the PXI-4130 if you aren't already using it).  Alternatively, you could set a voltage of zero and a small current limit (as low as 4uA) that would limit the flow of this current.  In that case you wouldn't actually 'disable' via software.

[GS]

I confirmed the behavior with the soft panels. I had a 3 V battery connected to channel 1. I set the mode to DC current and set the output value to 10 uA. With the output enabled, the current was 10 uA as measured by an external DMM. When I disabled the output the current went to about 12 mA.

George