Arc reports Negative baseline currents


#1

My application sleeps for 500 mSec then creates a 8mA spike for 5 mSec. I see a flat negative current of -20uA when it sleeps. Any ideas what can cause this?

I am running firmware 1.0.7 and calibrated after the download.


#2

Could you please share a short recording with us? Also, if you disconnect your device, does it settle with noise around 0 then?


#3

I am not sure how to share recordings.
here is a link to a project recording.low current mode.otii (1.5 MB)

Note the “min -48.9uA” shown in the top of the screen.


#4

I can see that the “low current mode.otii” project shows a recording in high-range which would explain the noise. Can you double check that the “Auto range” checkbox in the Current tab of the Project Settings window is checked?


#5

@wj1
Sorry for overtaking this rather old thread but I’m seeing the same issues as @doriteich (actually, we’re already discussing it via dm).
No matter the input settings, we always see negative current peaks. Auto range on/off, external supply (the one which is recommended here) vs. USB.
I’m just wondering how it affects the real world current draw as we use non-rechargeable batteries.
To get more specific:
I’ve exported the CSV and added column D which checks if column B is negative - and if it is, it returns 0 instead of the negative current.
Average current (as shown in OTII GUI) calculated by taking all raw values from column B is 140.95uA. Using 0 instead of negative current values, it is an average of 144.06uA. Not that much of a difference, I know, but I’m still wondering what the real world power consumption is.


#6

The real-world current consumption should include the negative spikes.

The negative current spikes occurs when the current consumption of the device under test is decreasing (rapidly), causing the output voltage to increase slightly. When the input capacitors of the Device Under Test are charged to this slightly elevated level this consumes some energy - this is the energy that is then drained when the voltage drops again, creating the negative spike.

The phenomenon is exaggerated with increased wire lead inductance.


#7

thanks @wj1! That helps a lot