pxi-4071 shielding cable

[alyast]

Hi, we use pxi-4071 on pxi-1033 for measurments and we connected shielded cables few meters long. We wrapped foil cables from the kit. After that we connected all the shields to the ground from the power supply. But we still remain interferences about 1nA and DC component 5nA. If anyone faced a similar problem, is it possible that we are too often measured current. Can you advise the shilded cables for multimeter in this case. 

[billko]

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@alyast wrote:

Hi, we use pxi-4071 on pxi-1033 for measurments and we connected shielded cables few meters long. We wrapped foil cables from the kit. After that we connected all the shields to the ground from the power supply. But we still remain interferences about 1nA and DC component 5nA. If anyone faced a similar problem, is it possible that we are too often measured current. Can you advise the shilded cables for multimeter in this case. 

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Does this have anything to do with LabVIEW?

[alyast]

Yes, we pretty sure in shielding, but we don't know why there is current constant component (5nA), while declared sensitivity - 0.1nA. Probably some bug with timing in LabView or something? I don't know what could be a reason for this behavior, and therefore ask noob questions.

[Steve_B]

Are you on the 100uA range of the 4071? You are indicating that there is a constant curent component which sounds like an offset. There will be an offset error that should fall within the specs for the range that you are using. It can vary based on many factors. You should be sure that your board has met the warm up requirements (1 hour) and performed a self calibration of the device which can be done in MAX or through the NI DMM API. 

The specs are also valid for the settings that are called out in the specifications document. For current that means 6.5 Digits, Autozero enabled, and ADC Calibration enabled. 

You can determine the impact of your setup by removing it from the equation, if you run your test with an open input you should read a current within the gain and offset specified for the range. If this reading looks good then you can spend some more time investigating your setup. 

Also the DMM forum would be a better place for the question which can be found here. 

[billko]

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@alyast wrote:

Yes, we pretty sure in shielding, but we don't know why there is current constant component (5nA), while declared sensitivity - 0.1nA. Probably some bug with timing in LabView or something? I don't know what could be a reason for this behavior, and therefore ask noob questions.

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Why would you suspect the software when all the evidence points to an issue with the HARDWARE?  And if you're measuring in the nanoAmp region, you'd better be ABSOLUTLEY certain that your grounds are true and accurate.  Probably grounding to your power supply is not good enough.  Your power supply probably has to be grounded to a copper stake going - what is, it, six feet? - into the ground.

[Steve_B]

The discussion has moved to the DMM forums.

pxi-4071 constant current