That is astounding!
It matches the reference curves so well it's hard to believe you can get such good performance with so little hardware.
This shows that a low priced USB based box could be sold for a few hundred dollars--certainly well under $1000!
This has got to be one of the neatest projects on the forum.
Thanks, I'm happy the amplification was quite successful. It's been a long, interesting, journey (I actually find it relaxing to work on
), while the instrument is quite usable, there are a few things I want to change, so I think it might be time for a new prototype soon.
The credit for the good performance has to go to the Analog Discovery unit, it is a very nice little device that packs a lot of power in a very small footprint. The dual 14 bit 125Msps ADC (AD9648) is pretty amazing.
But I might have painted a little too rosy picture of the performance in my eager to show what it can do. Under certain circumstances the results look significantly worse. e.g. measuring Rs of a small capacitor at low frequency. And Rs on inductor measurements is lower that what it should be.
Also you can see that the Dissipation factor is slightly below what it should be, but as long as it tracks nicely, I can easily live with that.
It is a bit time consuming to get a measurement like the one I posted earlier: I need to first let everything warm up, then do an open/short calibration, and then I can do the measurement.
And as you advised, being careful with calibration does indeed pay of, I have found that even the few nH in the tips of the Kelvin clamps can make a difference, so to make sure I get open/short at the same point I do it like this:
Open:
Short:
Do you only use open/short calibration, or do you use a reference as well?
Another issue I would like to have a look at is compensating for longer cables. Currently I have to use very short cables to get good results.