sensitivity PXIe 4082

[ASTDan]

Hello,

I am trying to determine the sensitivity (minimum value instrument can measure) for Resistance and Inductance measurements for the PXIe 4082.

Here is the spec sheet

https://www.ni.com/pdf/manuals/375256c.pdf

It lists the minimum range but not the sensitivity. 

I reposted this from the PXI forum.  I couldn't figure out how to move a post

http://forums.ni.com/t5/PXI/PXIe-4082-Sensitivity-measurments/td-p/3561345

Thanks

[Jake_H]

You can find the effective resolution of the DMM by looking at the noise graphs that immediately follow the DC voltage, current, and resistance accuracy tables. For resistance, if you look at the 100 Ohm range plot on page 6 of the specifications, you will see ~1 mOhm of rms resistance noise when using an aperture time of 100 ms. This plot provides supplemental information on how your aperture time affects the resolution of the measurement.

The inductance specs don't list the same level of detail that voltage, current, and resistance provide. If you want an estimate of the PXIe-4082 sensitivity before the holiday weekend, I would reference the specification document of the PXI-4072 (PXI version of this DMM), which has 1 nH resolution in the 10 uH range.

[ASTDan · Accepted solution]

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The reason sensitivity isn't explicitly defined in the spec sheet for the PXIe-4082 is because it's not always a clearly defined term. Therefore, it's not always practically useful. In some scenarios, "sensitivity" is taken to mean resolution. In others, it's sometimes understood as the smallest change displayed on the device readout. 

With that said, I think we should take a different approach to determine the quality of measurements the PXIe-4082 can do. We should be looking at the accuracy instead. The accuracy incorporates sensitivity, gain and offset errors, temperature drift, and other factors. I think this would therefore be the most relevant specification to you. 

If you refer back to the spec sheet (linked again below for convenience), you will find clear specifcations of accuracy for both resistance and inductance measurements. 

https://www.ni.com/pdf/manuals/375256c.pdf

To give you an idea of what some of these accuracy numbers look like, here's a brief example. Say we're measuring the resistance of a 220Ohm resistor. We would therefore be using the 1kOhm range of the DMM. If you look at page 5 of the spec sheet, you'll see that you can get your resistance measurements accurate within a specified uncertainty of +/-(some ppm of reading + some ppm of range). The numbers we will use for ppm are in Table 2. 

If your device was calibrated within the last two years for operation at room temperature, we would be able to expect a resistance measurement accurate within +/-(80 ppm of the reading + 15 ppm of the range). Therefore with our 220Ohm resistor being measured with our DMM's range of 1kOhm. We would get: 
220Ohm +/- ( (80ppm(220) + 15ppm(1000) ) 
This amounts to 220Ohm +/- (0.0326Ohm) 

Below I'm including links to two additional resources from our NI's website. The first discusses the accuracy, sensitivity, resolution, etc. of a DMM at a high level. The second has some sample accuracy calculations that I think will be helpful for you moving forward. 

http://www.ni.com/white-paper/3295/en/ 
http://www.ni.com/tutorial/3318/en/