Electronics > Metrology

Noise on LiPo batteries?

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alanambrose:
Yes, that's the one - 1995. It also has an interesting but brief description of the 'cross correlation fft' method....

The measurement methods don't look that difficult - assuming you have access to the previously-mentioned 'cross correlation fft'. A note here for instance:

http://dsp.stackexchange.com/questions/736/how-do-i-implement-cross-correlation-to-prove-two-audio-files-are-similar

and reference [3] in the original paper:

http://tf.nist.gov/general/pdf/90.pdf

Alan

mmagin:
Does the protection add to the noise?  I assume there's at least a mosfet in the path to provide the over-discharge cutoff.

I guess if you cared you could reimplement that with a really nice relay.

Kleinstein:
A MOSFET used as a switch should not give much noise. Usually this are low R_on MOSFETs, so a few mOhms of resistance. A relay might be more trouble with not so reliably contact resistance.

Cerebus:

--- Quote from: Kleinstein on May 07, 2016, 09:45:00 am ---A MOSFET used as a switch should not give much noise. Usually this are low R_on MOSFETs, so a few mOhms of resistance. A relay might be more trouble with not so reliably contact resistance.

--- End quote ---

Just to put some numbers on it, the Johnson noise of 1 mOhm is -228 dBv/sqrtHz so we are in the territory where we might care about it mucking up our measurements. In practical terms it's about -40 dB-bee's-dick, i.e. we don't care, but for measurements meant to establish the theoretical limits we might.

alanambrose:
Are you saying they were not just using a little 2 op amp test rig feeding a SR785 or similar? Sure looks that way, but maybe you have other ideas. I have not investigated fully but the x-correlation method on two similar sources to eliminate op amp noise with lots of samples sounds cute, no? I think this is a standard function in the SR785 and the Agilent equivalent unit. Ref [3] suggests that 'simple' method also.

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