PXI DMM 4071 DC current measurement accuracy

[Zack08]

Hi team,

I'm using PXI DMM 4071 to measure a DC current, and meet a problem with the result accuracy.

When current range is set to 1A, the measurement result is 0.015785, when current range is set to 0.1A, the measurement result is 0.01569.

Aperture time is 0.02s.

The two result is difference is almost 100uA. I'm quite confused, this is a 6.5 digit DMM, so even I change the range, the difference should be not so big at least. 

Could anyone help me or maybe some setup i did is wrong? Thanks in advance.

[Maxwell.B]

I've got a few questions that might help us make more sense of things:

1. What exactly are you expecting the reading to be?

2. Do you have an idea on which reading is more trustworthy?

3. How consistent are the readings if you take several measurements?

[Zack08]

Hi,

1. I'm not sure which reading is the correct one because the only thing I changed is the range from 1A to 0.1A.

2. I tested it for 10 times, the result is quite consistent. 

Do you have any idea?

[Maxwell.B]

The 4071 is an old DMM. Have you done the self calibration recently?

I looked through the help (LabVIEW >> Help >> NI Digital Multimeters Help), but you might do the same in case there's more there that goes into the equation. For a minute it looked like the settling time might need to be lengthened, but I'm thinking that's not the case since you're not measuring something above 100 mA.

Anyone have any ideas?

[Zack08]

Hi Maxwell,

This DMM is calibrated 1.5 years ago and the label on it says it needs re-calibration 4 months later.

I think I should use the 0.1A range but I cannot believe if I choose 1A range, the difference is so big(200uA). That's what I want to say. Is it normal to have such a difference even the DMM is newly calibrated?