Nordic Power Profiler Kit II, inaccurate charge (integral)

[T-moe]

I'm using the nordic ppk II to measure the power consumption of my device.

In order to validate the charge (current integral) displayed by the PPK2 i put two PPK2 daisy-chained into my current path. Both are configured as ampere meter and started at the same time. 
Even after a short while the two devices report different Charge. e.g. after 13 minutes one reports 24 Coulomb and the other 26 Coulomb.  Why is that? Can I somehow avoid this drift?

[Simonr]

Hi again

Thank you for the explanation. So, the reason you shouldn't connect two PPK2s in series like this, is mainly that the range switching of one of the PPKs can cause the other to switch in the wrong place and vice versa. They can switch on different places because they are differently calibrated. To confirm the setup you should do so one by one, with the given accuracy values for each kit. You're in danger of getting extra resistance in your path, and since both PPKs are calibrated down to 0R5, it will mess up the measurements for one of the kits to get extra series resistance in their path.

I double checked with one of the PPK devs, and leakage from one PPK to the other should not be a concern. Sorry about the confusion. But the above could still be an issue.

Best regards,

Simon

[T-moe]

Ok. That makes sense. I'll validate by measuring one by one.